Adding upstream version 110.0.1.upstream/110.0.1upstream

Signed-off-by: Daniel Baumann <daniel.baumann@progress-linux.org>

1 files changed, 2130 insertions, 0 deletions

diff --git a/gfx/wr/wrench/src/yaml_frame_reader.rs b/gfx/wr/wrench/src/yaml_frame_reader.rs
new file mode 100644
index 0000000000..698853f72d
--- /dev/null
+++ b/gfx/wr/wrench/src/yaml_frame_reader.rs
@@ -0,0 +1,2130 @@
+/* This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
+
+use euclid::SideOffsets2D;
+use gleam::gl;
+use image::GenericImageView;
+use crate::parse_function::parse_function;
+use crate::premultiply::premultiply;
+use std::collections::HashMap;
+use std::convert::TryInto;
+use std::fs::File;
+use std::io::Read;
+use std::path::{Path, PathBuf};
+use std::usize;
+use webrender::api::*;
+use webrender::render_api::*;
+use webrender::api::units::*;
+use webrender::api::FillRule;
+use crate::wrench::{FontDescriptor, Wrench, WrenchThing};
+use crate::yaml_helper::{StringEnum, YamlHelper, make_perspective};
+use yaml_rust::{Yaml, YamlLoader};
+use crate::PLATFORM_DEFAULT_FACE_NAME;
+
+macro_rules! try_intersect {
+    ($first: expr, $second: expr) => {
+        if let Some(rect) = ($first).intersection($second) {
+            rect
+        } else {
+            warn!("skipping item with non-intersecting bounds and clip_rect");
+            return;
+        }
+    }
+}
+
+fn rsrc_path(item: &Yaml, aux_dir: &Path) -> PathBuf {
+    let filename = item.as_str().unwrap();
+    let mut file = aux_dir.to_path_buf();
+    file.push(filename);
+    file
+}
+
+impl FontDescriptor {
+    fn from_yaml(item: &Yaml, aux_dir: &Path) -> FontDescriptor {
+        if !item["family"].is_badvalue() {
+            FontDescriptor::Properties {
+                family: item["family"].as_str().unwrap().to_owned(),
+                weight: item["weight"].as_i64().unwrap_or(400) as u32,
+                style: item["style"].as_i64().unwrap_or(0) as u32,
+                stretch: item["stretch"].as_i64().unwrap_or(5) as u32,
+            }
+        } else if !item["font"].is_badvalue() {
+            let path = rsrc_path(&item["font"], aux_dir);
+            FontDescriptor::Path {
+                path,
+                font_index: item["font-index"].as_i64().unwrap_or(0) as u32,
+            }
+        } else {
+            FontDescriptor::Family {
+                name: PLATFORM_DEFAULT_FACE_NAME.to_string(),
+            }
+        }
+    }
+}
+
+struct LocalExternalImageHandler {
+    texture_ids: Vec<(gl::GLuint, ImageDescriptor)>,
+}
+
+impl LocalExternalImageHandler {
+    pub fn new() -> LocalExternalImageHandler {
+        LocalExternalImageHandler {
+            texture_ids: Vec::new(),
+        }
+    }
+
+    fn init_gl_texture(
+        id: gl::GLuint,
+        gl_target: gl::GLuint,
+        format_desc: webrender::FormatDesc,
+        width: gl::GLint,
+        height: gl::GLint,
+        bytes: &[u8],
+        gl: &dyn gl::Gl,
+    ) {
+        gl.bind_texture(gl_target, id);
+        gl.tex_parameter_i(gl_target, gl::TEXTURE_MAG_FILTER, gl::LINEAR as gl::GLint);
+        gl.tex_parameter_i(gl_target, gl::TEXTURE_MIN_FILTER, gl::LINEAR as gl::GLint);
+        gl.tex_parameter_i(gl_target, gl::TEXTURE_WRAP_S, gl::CLAMP_TO_EDGE as gl::GLint);
+        gl.tex_parameter_i(gl_target, gl::TEXTURE_WRAP_T, gl::CLAMP_TO_EDGE as gl::GLint);
+        gl.tex_image_2d(
+            gl_target,
+            0,
+            format_desc.internal as gl::GLint,
+            width,
+            height,
+            0,
+            format_desc.external,
+            format_desc.pixel_type,
+            Some(bytes),
+        );
+        gl.bind_texture(gl_target, 0);
+    }
+
+    pub fn add_image(&mut self,
+        device: &webrender::Device,
+        desc: ImageDescriptor,
+        target: ImageBufferKind,
+        image_data: ImageData,
+    ) -> ImageData {
+        let (image_id, channel_idx) = match image_data {
+            ImageData::Raw(ref data) => {
+                let gl = device.gl();
+                let texture_ids = gl.gen_textures(1);
+                let format_desc = if desc.format == ImageFormat::BGRA8 {
+                    // Force BGRA8 data to RGBA8 layout to avoid potential
+                    // need for usage of texture-swizzle.
+                    webrender::FormatDesc {
+                        external: gl::BGRA,
+                        .. device.gl_describe_format(ImageFormat::RGBA8)
+                    }
+                } else {
+                    device.gl_describe_format(desc.format)
+                };
+
+                LocalExternalImageHandler::init_gl_texture(
+                    texture_ids[0],
+                    webrender::get_gl_target(target),
+                    format_desc,
+                    desc.size.width as gl::GLint,
+                    desc.size.height as gl::GLint,
+                    data,
+                    gl,
+                );
+                self.texture_ids.push((texture_ids[0], desc));
+                (ExternalImageId((self.texture_ids.len() - 1) as u64), 0)
+            },
+            _ => panic!("unsupported!"),
+        };
+
+        ImageData::External(
+            ExternalImageData {
+                id: image_id,
+                channel_index: channel_idx,
+                image_type: ExternalImageType::TextureHandle(target)
+            }
+        )
+    }
+}
+
+impl ExternalImageHandler for LocalExternalImageHandler {
+    fn lock(
+        &mut self,
+        key: ExternalImageId,
+        _channel_index: u8,
+    ) -> ExternalImage {
+        let (id, desc) = self.texture_ids[key.0 as usize];
+        ExternalImage {
+            uv: TexelRect::new(0.0, 0.0, desc.size.width as f32, desc.size.height as f32),
+            source: ExternalImageSource::NativeTexture(id),
+        }
+    }
+    fn unlock(&mut self, _key: ExternalImageId, _channel_index: u8) {}
+}
+
+fn broadcast<T: Clone>(base_vals: &[T], num_items: usize) -> Vec<T> {
+    if base_vals.len() == num_items {
+        return base_vals.to_vec();
+    }
+
+    assert_eq!(
+        num_items % base_vals.len(),
+        0,
+        "Cannot broadcast {} elements into {}",
+        base_vals.len(),
+        num_items
+    );
+
+    let mut vals = vec![];
+    loop {
+        if vals.len() == num_items {
+            break;
+        }
+        vals.extend_from_slice(base_vals);
+    }
+    vals
+}
+
+enum CheckerboardKind {
+    BlackGrey,
+    BlackTransparent,
+}
+
+fn generate_checkerboard_image(
+    border: u32,
+    tile_x_size: u32,
+    tile_y_size: u32,
+    tile_x_count: u32,
+    tile_y_count: u32,
+    kind: CheckerboardKind,
+) -> (ImageDescriptor, ImageData) {
+    let width = 2 * border + tile_x_size * tile_x_count;
+    let height = 2 * border + tile_y_size * tile_y_count;
+    let mut pixels = Vec::new();
+
+    for y in 0 .. height {
+        for x in 0 .. width {
+            if y < border || y >= (height - border) ||
+               x < border || x >= (width - border) {
+                pixels.push(0);
+                pixels.push(0);
+                pixels.push(0xff);
+                pixels.push(0xff);
+            } else {
+                let xon = ((x - border) % (2 * tile_x_size)) < tile_x_size;
+                let yon = ((y - border) % (2 * tile_y_size)) < tile_y_size;
+                match kind {
+                    CheckerboardKind::BlackGrey => {
+                        let value = if xon ^ yon { 0xff } else { 0x7f };
+                        pixels.push(value);
+                        pixels.push(value);
+                        pixels.push(value);
+                        pixels.push(0xff);
+                    }
+                    CheckerboardKind::BlackTransparent => {
+                        let value = if xon ^ yon { 0xff } else { 0x00 };
+                        pixels.push(value);
+                        pixels.push(value);
+                        pixels.push(value);
+                        pixels.push(value);
+                    }
+                }
+            }
+        }
+    }
+
+    let flags = match kind {
+        CheckerboardKind::BlackGrey => ImageDescriptorFlags::IS_OPAQUE,
+        CheckerboardKind::BlackTransparent => ImageDescriptorFlags::empty(),
+    };
+
+    (
+        ImageDescriptor::new(width as i32, height as i32, ImageFormat::BGRA8, flags),
+        ImageData::new(pixels),
+    )
+}
+
+fn generate_xy_gradient_image(w: u32, h: u32) -> (ImageDescriptor, ImageData) {
+    let mut pixels = Vec::with_capacity((w * h * 4) as usize);
+    for y in 0 .. h {
+        for x in 0 .. w {
+            let grid = if x % 100 < 3 || y % 100 < 3 { 0.9 } else { 1.0 };
+            pixels.push((y as f32 / h as f32 * 255.0 * grid) as u8);
+            pixels.push(0);
+            pixels.push((x as f32 / w as f32 * 255.0 * grid) as u8);
+            pixels.push(255);
+        }
+    }
+
+    (
+        ImageDescriptor::new(w as i32, h as i32, ImageFormat::BGRA8, ImageDescriptorFlags::IS_OPAQUE),
+        ImageData::new(pixels),
+    )
+}
+
+fn generate_solid_color_image(
+    r: u8,
+    g: u8,
+    b: u8,
+    a: u8,
+    w: u32,
+    h: u32,
+) -> (ImageDescriptor, ImageData) {
+    let num_pixels: usize = (w * h).try_into().unwrap();
+    let pixels = [b, g, r, a].repeat(num_pixels);
+
+    let mut flags = ImageDescriptorFlags::empty();
+    if a == 255 {
+        flags |= ImageDescriptorFlags::IS_OPAQUE;
+    }
+
+    (
+        ImageDescriptor::new(w as i32, h as i32, ImageFormat::BGRA8, flags),
+        ImageData::new(pixels),
+    )
+}
+
+
+
+fn is_image_opaque(format: ImageFormat, bytes: &[u8]) -> bool {
+    match format {
+        ImageFormat::BGRA8 |
+        ImageFormat::RGBA8 => {
+            let mut is_opaque = true;
+            for i in 0 .. (bytes.len() / 4) {
+                if bytes[i * 4 + 3] != 255 {
+                    is_opaque = false;
+                    break;
+                }
+            }
+            is_opaque
+        }
+        ImageFormat::RG8 => true,
+        ImageFormat::RG16 => true,
+        ImageFormat::R8 => false,
+        ImageFormat::R16 => false,
+        ImageFormat::RGBAF32 |
+        ImageFormat::RGBAI32 => unreachable!(),
+    }
+}
+
+struct IsRoot(bool);
+
+pub struct YamlFrameReader {
+    yaml_path: PathBuf,
+    aux_dir: PathBuf,
+    frame_count: u32,
+
+    display_lists: Vec<(PipelineId, BuiltDisplayList)>,
+
+    watch_source: bool,
+    list_resources: bool,
+
+    /// A HashMap of offsets which specify what scroll offsets particular
+    /// scroll layers should be initialized with.
+    scroll_offsets: HashMap<ExternalScrollId, Vec<SampledScrollOffset>>,
+    next_external_scroll_id: u64,
+
+    image_map: HashMap<(PathBuf, Option<i64>), (ImageKey, LayoutSize)>,
+
+    fonts: HashMap<FontDescriptor, FontKey>,
+    font_instances: HashMap<(FontKey, FontSize, FontInstanceFlags, Option<ColorU>, SyntheticItalics), FontInstanceKey>,
+    font_render_mode: Option<FontRenderMode>,
+    allow_mipmaps: bool,
+
+    /// A HashMap that allows specifying a numeric id for clip and clip chains in YAML
+    /// and having each of those ids correspond to a unique ClipId.
+    user_clip_id_map: HashMap<u64, ClipId>,
+    user_clipchain_id_map: HashMap<u64, ClipChainId>,
+    user_spatial_id_map: HashMap<u64, SpatialId>,
+
+    spatial_id_stack: Vec<SpatialId>,
+
+    requested_frame: usize,
+    built_frame: usize,
+
+    yaml_string: String,
+    keyframes: Option<Yaml>,
+
+    external_image_handler: Option<Box<LocalExternalImageHandler>>,
+
+    next_spatial_key: u64,
+}
+
+impl YamlFrameReader {
+    pub fn new(yaml_path: &Path) -> YamlFrameReader {
+        YamlFrameReader {
+            watch_source: false,
+            list_resources: false,
+            yaml_path: yaml_path.to_owned(),
+            aux_dir: yaml_path.parent().unwrap().to_owned(),
+            frame_count: 0,
+            display_lists: Vec::new(),
+            scroll_offsets: HashMap::new(),
+            fonts: HashMap::new(),
+            font_instances: HashMap::new(),
+            font_render_mode: None,
+            allow_mipmaps: false,
+            image_map: HashMap::new(),
+            user_clip_id_map: HashMap::new(),
+            user_clipchain_id_map: HashMap::new(),
+            user_spatial_id_map: HashMap::new(),
+            spatial_id_stack: Vec::new(),
+            yaml_string: String::new(),
+            requested_frame: 0,
+            built_frame: usize::MAX,
+            keyframes: None,
+            external_image_handler: Some(Box::new(LocalExternalImageHandler::new())),
+            next_external_scroll_id: 1000,      // arbitrary to easily see in logs which are implicit
+            next_spatial_key: 0,
+        }
+    }
+
+    pub fn deinit(mut self, wrench: &mut Wrench) {
+        let mut txn = Transaction::new();
+
+        for (_, font_instance) in self.font_instances.drain() {
+            txn.delete_font_instance(font_instance);
+        }
+
+        for (_, font) in self.fonts.drain() {
+            txn.delete_font(font);
+        }
+
+        wrench.api.send_transaction(wrench.document_id, txn);
+    }
+
+    fn top_space(&self) -> SpatialId {
+        *self.spatial_id_stack.last().unwrap()
+    }
+
+    pub fn yaml_path(&self) -> &PathBuf {
+        &self.yaml_path
+    }
+
+    pub fn new_from_args(args: &clap::ArgMatches) -> YamlFrameReader {
+        let yaml_file = args.value_of("INPUT").map(PathBuf::from).unwrap();
+
+        let mut y = YamlFrameReader::new(&yaml_file);
+
+        y.keyframes = args.value_of("keyframes").map(|path| {
+            let mut file = File::open(&path).unwrap();
+            let mut keyframes_string = String::new();
+            file.read_to_string(&mut keyframes_string).unwrap();
+            YamlLoader::load_from_str(&keyframes_string)
+                .expect("Failed to parse keyframes file")
+                .pop()
+                .unwrap()
+        });
+        y.list_resources = args.is_present("list-resources");
+        y.watch_source = args.is_present("watch");
+        y
+    }
+
+    pub fn reset(&mut self) {
+        self.scroll_offsets.clear();
+        self.display_lists.clear();
+    }
+
+    fn build(&mut self, wrench: &mut Wrench) {
+        let yaml = YamlLoader::load_from_str(&self.yaml_string)
+            .map(|mut yaml| {
+                assert_eq!(yaml.len(), 1);
+                yaml.pop().unwrap()
+            })
+            .expect("Failed to parse YAML file");
+
+        self.reset();
+
+        if let Some(pipelines) = yaml["pipelines"].as_vec() {
+            for pipeline in pipelines {
+                self.build_pipeline(wrench, pipeline["id"].as_pipeline_id().unwrap(), pipeline);
+            }
+        }
+
+        let root_stacking_context = &yaml["root"];
+        assert_ne!(*root_stacking_context, Yaml::BadValue);
+        self.build_pipeline(wrench, wrench.root_pipeline_id, root_stacking_context);
+
+        // If replaying the same frame during interactive use, the frame gets rebuilt,
+        // but the external image handler has already been consumed by the renderer.
+        if let Some(external_image_handler) = self.external_image_handler.take() {
+            wrench.renderer.set_external_image_handler(external_image_handler);
+        }
+    }
+
+    fn build_pipeline(
+        &mut self,
+        wrench: &mut Wrench,
+        pipeline_id: PipelineId,
+        yaml: &Yaml
+    ) {
+        // Don't allow referencing clips between pipelines for now.
+        self.user_clip_id_map.clear();
+        self.user_clipchain_id_map.clear();
+        self.user_spatial_id_map.clear();
+        self.spatial_id_stack.clear();
+        self.spatial_id_stack.push(SpatialId::root_scroll_node(pipeline_id));
+
+        let mut builder = DisplayListBuilder::new(pipeline_id);
+        builder.begin();
+        let mut info = CommonItemProperties {
+            clip_rect: LayoutRect::zero(),
+            clip_chain_id: ClipChainId::INVALID,
+            spatial_id: SpatialId::new(0, PipelineId::dummy()),
+            flags: PrimitiveFlags::default(),
+        };
+        self.add_stacking_context_from_yaml(&mut builder, wrench, yaml, IsRoot(true), &mut info);
+        self.display_lists.push(builder.end());
+
+        assert_eq!(self.spatial_id_stack.len(), 1);
+    }
+
+    fn to_clip_chain_id(
+        &self,
+        item: &Yaml,
+        builder: &mut DisplayListBuilder,
+    ) -> Option<ClipChainId> {
+        match *item {
+            Yaml::Integer(value) => {
+                Some(self.user_clipchain_id_map[&(value as u64)])
+            }
+            Yaml::Array(ref array) => {
+                let clip_ids: Vec<ClipId> = array
+                    .iter()
+                    .map(|id| {
+                        let id = id.as_i64().expect("invalid clip id") as u64;
+                        self.user_clip_id_map[&id]
+                    })
+                    .collect();
+
+                Some(builder.define_clip_chain(None, clip_ids))
+            }
+            _ => None,
+        }
+    }
+
+    fn to_spatial_id(&self, item: &Yaml, pipeline_id: PipelineId) -> Option<SpatialId> {
+        match *item {
+            Yaml::Integer(value) => Some(self.user_spatial_id_map[&(value as u64)]),
+            Yaml::String(ref id_string) if id_string == "root-reference-frame" =>
+                Some(SpatialId::root_reference_frame(pipeline_id)),
+            Yaml::String(ref id_string) if id_string == "root-scroll-node" =>
+                Some(SpatialId::root_scroll_node(pipeline_id)),
+            Yaml::BadValue => None,
+            _ => {
+                println!("Unable to parse SpatialId {:?}", item);
+                None
+            }
+        }
+    }
+
+    fn add_clip_id_mapping(&mut self, numeric_id: u64, real_id: ClipId) {
+        assert_ne!(numeric_id, 0, "id=0 is reserved for the root clip");
+        self.user_clip_id_map.insert(numeric_id, real_id);
+    }
+
+    fn add_clip_chain_id_mapping(&mut self, numeric_id: u64, real_id: ClipChainId) {
+        assert_ne!(numeric_id, 0, "id=0 is reserved for the root clip-chain");
+        self.user_clipchain_id_map.insert(numeric_id, real_id);
+    }
+
+    fn add_spatial_id_mapping(&mut self, numeric_id: u64, real_id: SpatialId) {
+        assert_ne!(numeric_id, 0, "id=0 is reserved for the root reference frame");
+        assert_ne!(numeric_id, 1, "id=1 is reserved for the root scroll node");
+        self.user_spatial_id_map.insert(numeric_id, real_id);
+    }
+
+    fn to_hit_testing_tag(&self, item: &Yaml) -> Option<ItemTag> {
+        match *item {
+            Yaml::Array(ref array) if array.len() == 2 => {
+                match (array[0].as_i64(), array[1].as_i64()) {
+                    (Some(first), Some(second)) => Some((first as u64, second as u16)),
+                    _ => None,
+                }
+            }
+            _ => None,
+        }
+
+    }
+
+    fn add_or_get_image(
+        &mut self,
+        file: &Path,
+        tiling: Option<i64>,
+        item: &Yaml,
+        wrench: &mut Wrench,
+    ) -> (ImageKey, LayoutSize) {
+        let key = (file.to_owned(), tiling);
+        if let Some(k) = self.image_map.get(&key) {
+            return *k;
+        }
+
+        if self.list_resources { println!("{}", file.to_string_lossy()); }
+        let (descriptor, image_data) = match image::open(file) {
+            Ok(image) => {
+                let (image_width, image_height) = image.dimensions();
+                let (format, bytes) = match image {
+                    image::DynamicImage::ImageLuma8(_) => {
+                        (ImageFormat::R8, image.to_bytes())
+                    }
+                    image::DynamicImage::ImageRgba8(_) => {
+                        let mut pixels = image.to_bytes();
+                        premultiply(pixels.as_mut_slice());
+                        (ImageFormat::BGRA8, pixels)
+                    }
+                    image::DynamicImage::ImageRgb8(_) => {
+                        let bytes = image.to_bytes();
+                        let mut pixels = Vec::with_capacity(image_width as usize * image_height as usize * 4);
+                        for bgr in bytes.chunks(3) {
+                            pixels.extend_from_slice(&[
+                                bgr[2],
+                                bgr[1],
+                                bgr[0],
+                                0xff
+                            ]);
+                        }
+                        (ImageFormat::BGRA8, pixels)
+                    }
+                    _ => panic!("We don't support whatever your crazy image type is, come on"),
+                };
+                let mut flags = ImageDescriptorFlags::empty();
+                if is_image_opaque(format, &bytes[..]) {
+                    flags |= ImageDescriptorFlags::IS_OPAQUE;
+                }
+                if self.allow_mipmaps {
+                    flags |= ImageDescriptorFlags::ALLOW_MIPMAPS;
+                }
+                let descriptor = ImageDescriptor::new(
+                    image_width as i32,
+                    image_height as i32,
+                    format,
+                    flags,
+                );
+                let data = ImageData::new(bytes);
+                (descriptor, data)
+            }
+            _ => {
+                // This is a hack but it is convenient when generating test cases and avoids
+                // bloating the repository.
+                match parse_function(
+                    file.components()
+                        .last()
+                        .unwrap()
+                        .as_os_str()
+                        .to_str()
+                        .unwrap(),
+                ) {
+                    ("xy-gradient", args, _) => generate_xy_gradient_image(
+                        args.get(0).unwrap_or(&"1000").parse::<u32>().unwrap(),
+                        args.get(1).unwrap_or(&"1000").parse::<u32>().unwrap(),
+                    ),
+                    ("solid-color", args, _) => generate_solid_color_image(
+                        args.get(0).unwrap_or(&"255").parse::<u8>().unwrap(),
+                        args.get(1).unwrap_or(&"255").parse::<u8>().unwrap(),
+                        args.get(2).unwrap_or(&"255").parse::<u8>().unwrap(),
+                        args.get(3).unwrap_or(&"255").parse::<u8>().unwrap(),
+                        args.get(4).unwrap_or(&"1000").parse::<u32>().unwrap(),
+                        args.get(5).unwrap_or(&"1000").parse::<u32>().unwrap(),
+                    ),
+                    (name @ "transparent-checkerboard", args, _) |
+                    (name @ "checkerboard", args, _) => {
+                        let border = args.get(0).unwrap_or(&"4").parse::<u32>().unwrap();
+
+                        let (x_size, y_size, x_count, y_count) = match args.len() {
+                            3 => {
+                                let size = args.get(1).unwrap_or(&"32").parse::<u32>().unwrap();
+                                let count = args.get(2).unwrap_or(&"8").parse::<u32>().unwrap();
+                                (size, size, count, count)
+                            }
+                            5 => {
+                                let x_size = args.get(1).unwrap_or(&"32").parse::<u32>().unwrap();
+                                let y_size = args.get(2).unwrap_or(&"32").parse::<u32>().unwrap();
+                                let x_count = args.get(3).unwrap_or(&"8").parse::<u32>().unwrap();
+                                let y_count = args.get(4).unwrap_or(&"8").parse::<u32>().unwrap();
+                                (x_size, y_size, x_count, y_count)
+                            }
+                            _ => {
+                                panic!("invalid checkerboard function");
+                            }
+                        };
+
+                        let kind = if name == "transparent-checkerboard" {
+                            CheckerboardKind::BlackTransparent
+                        } else {
+                            CheckerboardKind::BlackGrey
+                        };
+
+                        generate_checkerboard_image(
+                            border,
+                            x_size,
+                            y_size,
+                            x_count,
+                            y_count,
+                            kind,
+                        )
+                    }
+                    _ => {
+                        panic!("Failed to load image {:?}", file.to_str());
+                    }
+                }
+            }
+        };
+        let tiling = tiling.map(|tile_size| tile_size as u16);
+        let image_key = wrench.api.generate_image_key();
+        let mut txn = Transaction::new();
+
+        let external = item["external"].as_bool().unwrap_or(false);
+        if external {
+            // This indicates we want to simulate an external texture,
+            // ensure it gets created as such
+            let external_target = match item["external-target"].as_str() {
+                Some("2d") => ImageBufferKind::Texture2D,
+                Some("rect") => ImageBufferKind::TextureRect,
+                Some(t) => panic!("Unsupported external texture target: {}", t),
+                None => ImageBufferKind::Texture2D,
+            };
+
+            let external_image_data =
+                self.external_image_handler.as_mut().unwrap().add_image(
+                    &wrench.renderer.device,
+                    descriptor,
+                    external_target,
+                    image_data
+                );
+            txn.add_image(image_key, descriptor, external_image_data, tiling);
+        } else {
+            txn.add_image(image_key, descriptor, image_data, tiling);
+        }
+
+        wrench.api.send_transaction(wrench.document_id, txn);
+        let val = (
+            image_key,
+            LayoutSize::new(descriptor.size.width as f32, descriptor.size.height as f32),
+        );
+        self.image_map.insert(key, val);
+        val
+    }
+
+    fn get_or_create_font(&mut self, desc: FontDescriptor, wrench: &mut Wrench) -> FontKey {
+        let list_resources = self.list_resources;
+        *self.fonts
+            .entry(desc.clone())
+            .or_insert_with(|| match desc {
+                FontDescriptor::Path {
+                    ref path,
+                    font_index,
+                } => {
+                    if list_resources { println!("{}", path.to_string_lossy()); }
+                    let mut file = File::open(path).expect("Couldn't open font file");
+                    let mut bytes = vec![];
+                    file.read_to_end(&mut bytes)
+                        .expect("failed to read font file");
+                    wrench.font_key_from_bytes(bytes, font_index)
+                }
+                FontDescriptor::Family { ref name } => wrench.font_key_from_name(name),
+                FontDescriptor::Properties {
+                    ref family,
+                    weight,
+                    style,
+                    stretch,
+                } => wrench.font_key_from_properties(family, weight, style, stretch),
+            })
+    }
+
+    pub fn allow_mipmaps(&mut self, allow_mipmaps: bool) {
+        self.allow_mipmaps = allow_mipmaps;
+    }
+
+    pub fn set_font_render_mode(&mut self, render_mode: Option<FontRenderMode>) {
+        self.font_render_mode = render_mode;
+    }
+
+    fn get_or_create_font_instance(
+        &mut self,
+        font_key: FontKey,
+        size: f32,
+        bg_color: Option<ColorU>,
+        flags: FontInstanceFlags,
+        synthetic_italics: SyntheticItalics,
+        wrench: &mut Wrench,
+    ) -> FontInstanceKey {
+        let font_render_mode = self.font_render_mode;
+
+        *self.font_instances
+            .entry((font_key, size.into(), flags, bg_color, synthetic_italics))
+            .or_insert_with(|| {
+                wrench.add_font_instance(
+                    font_key,
+                    size,
+                    flags,
+                    font_render_mode,
+                    bg_color,
+                    synthetic_italics,
+                )
+            })
+    }
+
+    fn as_image_mask(&mut self, item: &Yaml, wrench: &mut Wrench) -> Option<ImageMask> {
+        item.as_hash()?;
+
+        let tiling = item["tile-size"].as_i64();
+
+        let (image_key, image_dims) = match item["image"].as_str() {
+            Some("invalid") => (ImageKey::DUMMY, LayoutSize::new(100.0, 100.0)),
+            Some(filename) => {
+                let mut file = self.aux_dir.clone();
+                file.push(filename);
+                self.add_or_get_image(&file, tiling, item, wrench)
+            }
+            None => {
+                warn!("No image provided for the image-mask!");
+                return None;
+            }
+        };
+
+        let image_rect = item["rect"]
+            .as_rect()
+            .unwrap_or_else(|| LayoutRect::from_size(image_dims));
+        Some(ImageMask {
+            image: image_key,
+            rect: image_rect,
+        })
+    }
+
+    fn handle_rect(
+        &self,
+        dl: &mut DisplayListBuilder,
+        item: &Yaml,
+        info: &CommonItemProperties,
+    ) {
+        let bounds_key = if item["type"].is_badvalue() {
+            "rect"
+        } else {
+            "bounds"
+        };
+
+        let bounds = self.resolve_rect(&item[bounds_key]);
+        let color = self.resolve_colorf(&item["color"]).unwrap_or(ColorF::BLACK);
+        dl.push_rect(info, bounds, color);
+    }
+
+    fn handle_clear_rect(
+        &self,
+        dl: &mut DisplayListBuilder,
+        item: &Yaml,
+        info: &CommonItemProperties,
+    ) {
+        let bounds = item["bounds"].as_rect().expect("clear-rect type must have bounds");
+        dl.push_clear_rect(info, bounds);
+    }
+
+    fn handle_hit_test(
+        &mut self,
+        dl: &mut DisplayListBuilder,
+        item: &Yaml,
+        info: &mut CommonItemProperties,
+    ) {
+        info.clip_rect = try_intersect!(
+            item["bounds"].as_rect().expect("hit-test type must have bounds"),
+            &info.clip_rect
+        );
+
+        if let Some(tag) = self.to_hit_testing_tag(&item["hit-testing-tag"]) {
+            dl.push_hit_test(
+                info.clip_rect,
+                info.clip_chain_id,
+                info.spatial_id,
+                info.flags,
+                tag,
+            );
+        }
+    }
+
+    fn handle_line(
+        &mut self,
+        dl: &mut DisplayListBuilder,
+        item: &Yaml,
+        info: &mut CommonItemProperties,
+    ) {
+        let color = item["color"].as_colorf().unwrap_or(ColorF::BLACK);
+        let orientation = item["orientation"]
+            .as_str()
+            .and_then(LineOrientation::from_str)
+            .expect("line must have orientation");
+        let style = item["style"]
+            .as_str()
+            .and_then(LineStyle::from_str)
+            .expect("line must have style");
+
+        let wavy_line_thickness = if let LineStyle::Wavy = style {
+            item["thickness"].as_f32().expect("wavy lines must have a thickness")
+        } else {
+            0.0
+        };
+
+        let area = if item["baseline"].is_badvalue() {
+            let bounds_key = if item["type"].is_badvalue() {
+                "rect"
+            } else {
+                "bounds"
+            };
+
+            item[bounds_key]
+                .as_rect()
+                .expect("line type must have bounds")
+        } else {
+            // Legacy line representation
+            let baseline = item["baseline"].as_f32().expect("line must have baseline");
+            let start = item["start"].as_f32().expect("line must have start");
+            let end = item["end"].as_f32().expect("line must have end");
+            let width = item["width"].as_f32().expect("line must have width");
+
+            match orientation {
+                LineOrientation::Horizontal => {
+                    LayoutRect::from_origin_and_size(
+                        LayoutPoint::new(start, baseline),
+                        LayoutSize::new(end - start, width),
+                    )
+                }
+                LineOrientation::Vertical => {
+                    LayoutRect::from_origin_and_size(
+                        LayoutPoint::new(baseline, start),
+                        LayoutSize::new(width, end - start),
+                    )
+                }
+            }
+            };
+
+        dl.push_line(
+            info,
+            &area,
+            wavy_line_thickness,
+            orientation,
+            &color,
+            style,
+        );
+    }
+
+    fn handle_gradient(
+        &mut self,
+        dl: &mut DisplayListBuilder,
+        item: &Yaml,
+        info: &mut CommonItemProperties,
+    ) {
+        let bounds_key = if item["type"].is_badvalue() {
+            "gradient"
+        } else {
+            "bounds"
+        };
+        let bounds = item[bounds_key]
+            .as_rect()
+            .expect("gradient must have bounds");
+
+        let gradient = item.as_gradient(dl);
+        let tile_size = item["tile-size"].as_size().unwrap_or_else(|| bounds.size());
+        let tile_spacing = item["tile-spacing"].as_size().unwrap_or_else(LayoutSize::zero);
+
+        dl.push_gradient(
+            info,
+            bounds,
+            gradient,
+            tile_size,
+            tile_spacing
+        );
+    }
+
+    fn handle_radial_gradient(
+        &mut self,
+        dl: &mut DisplayListBuilder,
+        item: &Yaml,
+        info: &mut CommonItemProperties,
+    ) {
+        let bounds_key = if item["type"].is_badvalue() {
+            "radial-gradient"
+        } else {
+            "bounds"
+        };
+        let bounds = item[bounds_key]
+            .as_rect()
+            .expect("radial gradient must have bounds");
+        let gradient = item.as_radial_gradient(dl);
+        let tile_size = item["tile-size"].as_size().unwrap_or_else(|| bounds.size());
+        let tile_spacing = item["tile-spacing"].as_size().unwrap_or_else(LayoutSize::zero);
+
+        dl.push_radial_gradient(
+            info,
+            bounds,
+            gradient,
+            tile_size,
+            tile_spacing,
+        );
+    }
+
+    fn handle_conic_gradient(
+        &mut self,
+        dl: &mut DisplayListBuilder,
+        item: &Yaml,
+        info: &mut CommonItemProperties,
+    ) {
+        let bounds_key = if item["type"].is_badvalue() {
+            "conic-gradient"
+        } else {
+            "bounds"
+        };
+        let bounds = item[bounds_key]
+            .as_rect()
+            .expect("conic gradient must have bounds");
+        let gradient = item.as_conic_gradient(dl);
+        let tile_size = item["tile-size"].as_size().unwrap_or_else(|| bounds.size());
+        let tile_spacing = item["tile-spacing"].as_size().unwrap_or_else(LayoutSize::zero);
+
+        dl.push_conic_gradient(
+            info,
+            bounds,
+            gradient,
+            tile_size,
+            tile_spacing,
+        );
+    }
+
+    fn handle_border(
+        &mut self,
+        dl: &mut DisplayListBuilder,
+        wrench: &mut Wrench,
+        item: &Yaml,
+        info: &mut CommonItemProperties,
+    ) {
+        let bounds_key = if item["type"].is_badvalue() {
+            "border"
+        } else {
+            "bounds"
+        };
+        let bounds = item[bounds_key].as_rect().expect("borders must have bounds");
+        let widths = item["width"]
+            .as_vec_f32()
+            .expect("borders must have width(s)");
+        let widths = broadcast(&widths, 4);
+        let widths = LayoutSideOffsets::new(widths[0], widths[3], widths[2], widths[1]);
+        let border_details = if let Some(border_type) = item["border-type"].as_str() {
+            match border_type {
+                "normal" => {
+                    let colors = item["color"]
+                        .as_vec_colorf()
+                        .expect("borders must have color(s)");
+                    let styles = item["style"]
+                        .as_vec_string()
+                        .expect("borders must have style(s)");
+                    let styles = styles
+                        .iter()
+                        .map(|s| match s.as_str() {
+                            "none" => BorderStyle::None,
+                            "solid" => BorderStyle::Solid,
+                            "double" => BorderStyle::Double,
+                            "dotted" => BorderStyle::Dotted,
+                            "dashed" => BorderStyle::Dashed,
+                            "hidden" => BorderStyle::Hidden,
+                            "ridge" => BorderStyle::Ridge,
+                            "inset" => BorderStyle::Inset,
+                            "outset" => BorderStyle::Outset,
+                            "groove" => BorderStyle::Groove,
+                            s => {
+                                panic!("Unknown border style '{}'", s);
+                            }
+                        })
+                        .collect::<Vec<BorderStyle>>();
+                    let radius = item["radius"]
+                        .as_border_radius()
+                        .unwrap_or_else(BorderRadius::zero);
+
+                    let colors = broadcast(&colors, 4);
+                    let styles = broadcast(&styles, 4);
+
+                    let top = BorderSide {
+                        color: colors[0],
+                        style: styles[0],
+                    };
+                    let right = BorderSide {
+                        color: colors[1],
+                        style: styles[1],
+                    };
+                    let bottom = BorderSide {
+                        color: colors[2],
+                        style: styles[2],
+                    };
+                    let left = BorderSide {
+                        color: colors[3],
+                        style: styles[3],
+                    };
+                    let do_aa = item["do_aa"].as_bool().unwrap_or(true);
+                    Some(BorderDetails::Normal(NormalBorder {
+                        top,
+                        left,
+                        bottom,
+                        right,
+                        radius,
+                        do_aa,
+                    }))
+                }
+                "image" | "gradient" | "radial-gradient" | "conic-gradient" => {
+                    let image_width = item["image-width"]
+                        .as_i64()
+                        .unwrap_or(bounds.width() as i64);
+                    let image_height = item["image-height"]
+                        .as_i64()
+                        .unwrap_or(bounds.height() as i64);
+                    let fill = item["fill"].as_bool().unwrap_or(false);
+
+                    let slice = if let Some(slice) = item["slice"].as_vec_u32() {
+                        broadcast(&slice, 4)
+                    } else {
+                        vec![widths.top as u32, widths.left as u32, widths.bottom as u32, widths.right as u32]
+                    };
+
+                    let outset = item["outset"]
+                        .as_vec_f32()
+                        .expect("border must have outset");
+                    let outset = broadcast(&outset, 4);
+                    let repeat_horizontal = match item["repeat-horizontal"]
+                        .as_str()
+                        .unwrap_or("stretch")
+                    {
+                        "stretch" => RepeatMode::Stretch,
+                        "repeat" => RepeatMode::Repeat,
+                        "round" => RepeatMode::Round,
+                        "space" => RepeatMode::Space,
+                        s => panic!("Unknown box border image repeat mode {}", s),
+                    };
+                    let repeat_vertical = match item["repeat-vertical"]
+                        .as_str()
+                        .unwrap_or("stretch")
+                    {
+                        "stretch" => RepeatMode::Stretch,
+                        "repeat" => RepeatMode::Repeat,
+                        "round" => RepeatMode::Round,
+                        "space" => RepeatMode::Space,
+                        s => panic!("Unknown box border image repeat mode {}", s),
+                    };
+                    let source = match border_type {
+                        "image" => {
+                            let file = rsrc_path(&item["image-source"], &self.aux_dir);
+                            let (image_key, _) = self
+                                .add_or_get_image(&file, None, item, wrench);
+                            NinePatchBorderSource::Image(image_key, ImageRendering::Auto)
+                        }
+                        "gradient" => {
+                            let gradient = item.as_gradient(dl);
+                            NinePatchBorderSource::Gradient(gradient)
+                        }
+                        "radial-gradient" => {
+                            let gradient = item.as_radial_gradient(dl);
+                            NinePatchBorderSource::RadialGradient(gradient)
+                        }
+                        "conic-gradient" => {
+                            let gradient = item.as_conic_gradient(dl);
+                            NinePatchBorderSource::ConicGradient(gradient)
+                        }
+                        _ => unreachable!("Unexpected border type"),
+                    };
+
+                    Some(BorderDetails::NinePatch(NinePatchBorder {
+                        source,
+                        width: image_width as i32,
+                        height: image_height as i32,
+                        slice: SideOffsets2D::new(slice[0] as i32, slice[1] as i32, slice[2] as i32, slice[3] as i32),
+                        fill,
+                        repeat_horizontal,
+                        repeat_vertical,
+                        outset: SideOffsets2D::new(outset[0], outset[1], outset[2], outset[3]),
+                    }))
+                }
+                _ => {
+                    println!("Unable to parse border {:?}", item);
+                    None
+                }
+            }
+        } else {
+            println!("Unable to parse border {:?}", item);
+            None
+        };
+        if let Some(details) = border_details {
+            dl.push_border(info, bounds, widths, details);
+        }
+    }
+
+    fn handle_box_shadow(
+        &mut self,
+        dl: &mut DisplayListBuilder,
+        item: &Yaml,
+        info: &mut CommonItemProperties,
+    ) {
+        let bounds_key = if item["type"].is_badvalue() {
+            "box-shadow"
+        } else {
+            "bounds"
+        };
+        let bounds = item[bounds_key]
+            .as_rect()
+            .expect("box shadow must have bounds");
+        let box_bounds = item["box-bounds"].as_rect().unwrap_or(bounds);
+        let offset = self.resolve_vector(&item["offset"], LayoutVector2D::zero());
+        let color = item["color"]
+            .as_colorf()
+            .unwrap_or_else(|| ColorF::new(0.0, 0.0, 0.0, 1.0));
+        let blur_radius = item["blur-radius"].as_force_f32().unwrap_or(0.0);
+        let spread_radius = item["spread-radius"].as_force_f32().unwrap_or(0.0);
+        let border_radius = item["border-radius"]
+            .as_border_radius()
+            .unwrap_or_else(BorderRadius::zero);
+        let clip_mode = if let Some(mode) = item["clip-mode"].as_str() {
+            match mode {
+                "outset" => BoxShadowClipMode::Outset,
+                "inset" => BoxShadowClipMode::Inset,
+                s => panic!("Unknown box shadow clip mode {}", s),
+            }
+        } else {
+            BoxShadowClipMode::Outset
+        };
+
+        dl.push_box_shadow(
+            info,
+            box_bounds,
+            offset,
+            color,
+            blur_radius,
+            spread_radius,
+            border_radius,
+            clip_mode,
+        );
+    }
+
+    fn handle_yuv_image(
+        &mut self,
+        dl: &mut DisplayListBuilder,
+        wrench: &mut Wrench,
+        item: &Yaml,
+        info: &mut CommonItemProperties,
+    ) {
+        // TODO(gw): Support other YUV color depth and spaces.
+        let color_depth = ColorDepth::Color8;
+        let color_space = YuvColorSpace::Rec709;
+        let color_range = ColorRange::Limited;
+
+        let yuv_data = match item["format"].as_str().expect("no format supplied") {
+            "planar" => {
+                let y_path = rsrc_path(&item["src-y"], &self.aux_dir);
+                let (y_key, _) = self.add_or_get_image(&y_path, None, item, wrench);
+
+                let u_path = rsrc_path(&item["src-u"], &self.aux_dir);
+                let (u_key, _) = self.add_or_get_image(&u_path, None, item, wrench);
+
+                let v_path = rsrc_path(&item["src-v"], &self.aux_dir);
+                let (v_key, _) = self.add_or_get_image(&v_path, None, item, wrench);
+
+                YuvData::PlanarYCbCr(y_key, u_key, v_key)
+            }
+            "nv12" => {
+                let y_path = rsrc_path(&item["src-y"], &self.aux_dir);
+                let (y_key, _) = self.add_or_get_image(&y_path, None, item, wrench);
+
+                let uv_path = rsrc_path(&item["src-uv"], &self.aux_dir);
+                let (uv_key, _) = self.add_or_get_image(&uv_path, None, item, wrench);
+
+                YuvData::NV12(y_key, uv_key)
+            }
+            "p010" => {
+                let y_path = rsrc_path(&item["src-y"], &self.aux_dir);
+                let (y_key, _) = self.add_or_get_image(&y_path, None, item, wrench);
+
+                let uv_path = rsrc_path(&item["src-uv"], &self.aux_dir);
+                let (uv_key, _) = self.add_or_get_image(&uv_path, None, item, wrench);
+
+                YuvData::P010(y_key, uv_key)
+            }
+            "interleaved" => {
+                let yuv_path = rsrc_path(&item["src"], &self.aux_dir);
+                let (yuv_key, _) = self.add_or_get_image(&yuv_path, None, item, wrench);
+
+                YuvData::InterleavedYCbCr(yuv_key)
+            }
+            _ => {
+                panic!("unexpected yuv format");
+            }
+        };
+
+        let bounds = item["bounds"].as_vec_f32().unwrap();
+        let bounds = LayoutRect::from_origin_and_size(
+            LayoutPoint::new(bounds[0], bounds[1]),
+            LayoutSize::new(bounds[2], bounds[3]),
+        );
+
+        dl.push_yuv_image(
+            info,
+            bounds,
+            yuv_data,
+            color_depth,
+            color_space,
+            color_range,
+            ImageRendering::Auto,
+        );
+    }
+
+    fn handle_image(
+        &mut self,
+        dl: &mut DisplayListBuilder,
+        wrench: &mut Wrench,
+        item: &Yaml,
+        info: &mut CommonItemProperties,
+    ) {
+        let filename = &item[if item["type"].is_badvalue() {
+                                 "image"
+                             } else {
+                                 "src"
+                             }];
+        let tiling = item["tile-size"].as_i64();
+        let file = rsrc_path(filename, &self.aux_dir);
+        let (image_key, image_dims) =
+            self.add_or_get_image(&file, tiling, item, wrench);
+
+        let bounds_raws = item["bounds"].as_vec_f32().unwrap();
+        let bounds = if bounds_raws.len() == 2 {
+            LayoutRect::from_origin_and_size(LayoutPoint::new(bounds_raws[0], bounds_raws[1]), image_dims)
+        } else if bounds_raws.len() == 4 {
+            LayoutRect::from_origin_and_size(
+                LayoutPoint::new(bounds_raws[0], bounds_raws[1]),
+                LayoutSize::new(bounds_raws[2], bounds_raws[3]),
+            )
+        } else {
+            panic!(
+                "image expected 2 or 4 values in bounds, got '{:?}'",
+                item["bounds"]
+            );
+        };
+        let rendering = match item["rendering"].as_str() {
+            Some("auto") | None => ImageRendering::Auto,
+            Some("crisp-edges") => ImageRendering::CrispEdges,
+            Some("pixelated") => ImageRendering::Pixelated,
+            Some(_) => panic!(
+                "ImageRendering can be auto, crisp-edges, or pixelated -- got {:?}",
+                item
+            ),
+        };
+        let alpha_type = match item["alpha-type"].as_str() {
+            Some("premultiplied-alpha") | None => AlphaType::PremultipliedAlpha,
+            Some("alpha") => AlphaType::Alpha,
+            Some(_) => panic!(
+                "AlphaType can be premultiplied-alpha or alpha -- got {:?}",
+                item
+            ),
+        };
+        let color = item["color"]
+            .as_colorf()
+            .unwrap_or_else(|| ColorF::WHITE);
+        let stretch_size = item["stretch-size"].as_size();
+        let tile_spacing = item["tile-spacing"].as_size();
+        if stretch_size.is_none() && tile_spacing.is_none() {
+            dl.push_image(
+                info,
+                bounds,
+                rendering,
+                alpha_type,
+                image_key,
+                color,
+           );
+        } else {
+            dl.push_repeating_image(
+                info,
+                bounds,
+                stretch_size.unwrap_or(image_dims),
+                tile_spacing.unwrap_or_else(LayoutSize::zero),
+                rendering,
+                alpha_type,
+                image_key,
+                color,
+           );
+        }
+    }
+
+    fn handle_text(
+        &mut self,
+        dl: &mut DisplayListBuilder,
+        wrench: &mut Wrench,
+        item: &Yaml,
+        info: &mut CommonItemProperties,
+    ) {
+        let size = item["size"].as_pt_to_f32().unwrap_or(16.0);
+        let color = item["color"].as_colorf().unwrap_or(ColorF::BLACK);
+        let bg_color = item["bg-color"].as_colorf().map(|c| c.into());
+        let synthetic_italics = if let Some(angle) = item["synthetic-italics"].as_f32() {
+            SyntheticItalics::from_degrees(angle)
+        } else if item["synthetic-italics"].as_bool().unwrap_or(false) {
+            SyntheticItalics::enabled()
+        } else {
+            SyntheticItalics::disabled()
+        };
+
+        let mut flags = FontInstanceFlags::empty();
+        if item["synthetic-bold"].as_bool().unwrap_or(false) {
+            flags |= FontInstanceFlags::SYNTHETIC_BOLD;
+        }
+        if item["embedded-bitmaps"].as_bool().unwrap_or(false) {
+            flags |= FontInstanceFlags::EMBEDDED_BITMAPS;
+        }
+        if item["transpose"].as_bool().unwrap_or(false) {
+            flags |= FontInstanceFlags::TRANSPOSE;
+        }
+        if item["flip-x"].as_bool().unwrap_or(false) {
+            flags |= FontInstanceFlags::FLIP_X;
+        }
+        if item["flip-y"].as_bool().unwrap_or(false) {
+            flags |= FontInstanceFlags::FLIP_Y;
+        }
+
+        assert!(
+            item["blur-radius"].is_badvalue(),
+            "text no longer has a blur radius, use PushShadow and PopAllShadows"
+        );
+
+        let desc = FontDescriptor::from_yaml(item, &self.aux_dir);
+        let font_key = self.get_or_create_font(desc, wrench);
+        let font_instance_key = self.get_or_create_font_instance(font_key,
+                                                                 size,
+                                                                 bg_color,
+                                                                 flags,
+                                                                 synthetic_italics,
+                                                                 wrench);
+
+        assert!(
+            !(item["glyphs"].is_badvalue() && item["text"].is_badvalue()),
+            "text item had neither text nor glyphs!"
+        );
+
+        let (glyphs, rect) = if item["text"].is_badvalue() {
+            // if glyphs are specified, then the glyph positions can have the
+            // origin baked in.
+            let origin = item["origin"]
+                .as_point()
+                .unwrap_or(LayoutPoint::new(0.0, 0.0));
+            let glyph_indices = item["glyphs"].as_vec_u32().unwrap();
+            let glyph_offsets = item["offsets"].as_vec_f32().unwrap();
+            assert_eq!(glyph_offsets.len(), glyph_indices.len() * 2);
+
+            let glyphs = glyph_indices
+                .iter()
+                .enumerate()
+                .map(|k| {
+                    GlyphInstance {
+                        index: *k.1,
+                        // In the future we want to change the API to be relative, eliminating this
+                        point: LayoutPoint::new(
+                            origin.x + glyph_offsets[k.0 * 2],
+                            origin.y + glyph_offsets[k.0 * 2 + 1],
+                        ),
+                    }
+                })
+                .collect::<Vec<_>>();
+            // TODO(gw): We could optionally use the WR API to query glyph dimensions
+            //           here and calculate the bounding region here if we want to.
+            let rect = item["bounds"]
+                .as_rect()
+                .expect("Text items with glyphs require bounds [for now]");
+            (glyphs, rect)
+        } else {
+            let text = item["text"].as_str().unwrap();
+            let origin = item["origin"]
+                .as_point()
+                .expect("origin required for text without glyphs");
+            let (glyph_indices, glyph_positions, bounds) = wrench.layout_simple_ascii(
+                font_key,
+                font_instance_key,
+                text,
+                size,
+                origin,
+                flags,
+            );
+
+            let glyphs = glyph_indices
+                .iter()
+                .zip(glyph_positions)
+                .map(|arg| {
+                    GlyphInstance {
+                        index: *arg.0 as u32,
+                        point: arg.1,
+                    }
+                })
+                .collect::<Vec<_>>();
+            (glyphs, bounds)
+        };
+
+        dl.push_text(
+            info,
+            rect,
+            &glyphs,
+            font_instance_key,
+            color,
+            None,
+        );
+    }
+
+    fn handle_iframe(
+        &mut self,
+        dl: &mut DisplayListBuilder,
+        item: &Yaml,
+        info: &mut CommonItemProperties,
+    ) {
+        let bounds = item["bounds"].as_rect().expect("iframe must have bounds");
+        let pipeline_id = item["id"].as_pipeline_id().unwrap();
+        let ignore = item["ignore_missing_pipeline"].as_bool().unwrap_or(true);
+        dl.push_iframe(
+            bounds,
+            info.clip_rect,
+            &SpaceAndClipInfo {
+                spatial_id: info.spatial_id,
+                clip_chain_id: info.clip_chain_id
+            },
+            pipeline_id,
+            ignore
+        );
+    }
+
+    fn get_item_type_from_yaml(item: &Yaml) -> &str {
+        let shorthands = [
+            "rect",
+            "image",
+            "text",
+            "glyphs",
+            "box-shadow", // Note: box_shadow shorthand check has to come before border.
+            "border",
+            "gradient",
+            "radial-gradient",
+            "conic-gradient"
+        ];
+
+        for shorthand in shorthands.iter() {
+            if !item[*shorthand].is_badvalue() {
+                return shorthand;
+            }
+        }
+        item["type"].as_str().unwrap_or("unknown")
+    }
+
+    fn add_display_list_items_from_yaml(
+        &mut self,
+        dl: &mut DisplayListBuilder,
+        wrench: &mut Wrench,
+        yaml_items: &[Yaml],
+    ) {
+        // A very large number (but safely far away from finite limits of f32)
+        let big_number = 1.0e30;
+        // A rect that should in practical terms serve as a no-op for clipping
+        let full_clip = LayoutRect::from_origin_and_size(
+            LayoutPoint::new(-big_number / 2.0, -big_number / 2.0),
+            LayoutSize::new(big_number, big_number));
+
+        for item in yaml_items {
+            let item_type = Self::get_item_type_from_yaml(item);
+
+            let spatial_id = self.to_spatial_id(&item["spatial-id"], dl.pipeline_id);
+
+            if let Some(spatial_id) = spatial_id {
+                self.spatial_id_stack.push(spatial_id);
+            }
+
+            let clip_rect = item["clip-rect"].as_rect().unwrap_or(full_clip);
+            let clip_chain_id = self.to_clip_chain_id(&item["clip-chain"], dl).unwrap_or(ClipChainId::INVALID);
+
+            let mut flags = PrimitiveFlags::default();
+            for (key, flag) in [
+                ("backface-visible", PrimitiveFlags::IS_BACKFACE_VISIBLE),
+                ("scrollbar-container", PrimitiveFlags::IS_SCROLLBAR_CONTAINER),
+                ("prefer-compositor-surface", PrimitiveFlags::PREFER_COMPOSITOR_SURFACE),
+            ] {
+                if let Some(value) = item[key].as_bool() {
+                    flags.set(flag, value);
+                }
+            }
+
+
+            let mut info = CommonItemProperties {
+                clip_rect,
+                clip_chain_id,
+                spatial_id: self.top_space(),
+                flags,
+            };
+
+            match item_type {
+                "rect" => self.handle_rect(dl, item, &info),
+                "hit-test" => self.handle_hit_test(dl, item, &mut info),
+                "clear-rect" => self.handle_clear_rect(dl, item, &info),
+                "line" => self.handle_line(dl, item, &mut info),
+                "image" => self.handle_image(dl, wrench, item, &mut info),
+                "yuv-image" => self.handle_yuv_image(dl, wrench, item, &mut info),
+                "text" | "glyphs" => self.handle_text(dl, wrench, item, &mut info),
+                "scroll-frame" => self.handle_scroll_frame(dl, wrench, item),
+                "sticky-frame" => self.handle_sticky_frame(dl, wrench, item),
+                "clip" => self.handle_clip(dl, wrench, item),
+                "clip-chain" => self.handle_clip_chain(dl, item),
+                "border" => self.handle_border(dl, wrench, item, &mut info),
+                "gradient" => self.handle_gradient(dl, item, &mut info),
+                "radial-gradient" => self.handle_radial_gradient(dl, item, &mut info),
+                "conic-gradient" => self.handle_conic_gradient(dl, item, &mut info),
+                "box-shadow" => self.handle_box_shadow(dl, item, &mut info),
+                "iframe" => self.handle_iframe(dl, item, &mut info),
+                "stacking-context" => {
+                    self.add_stacking_context_from_yaml(dl, wrench, item, IsRoot(false), &mut info)
+                }
+                "reference-frame" => self.handle_reference_frame(dl, wrench, item),
+                "computed-frame" => self.handle_computed_frame(dl, wrench, item),
+                "shadow" => self.handle_push_shadow(dl, item, &mut info),
+                "pop-all-shadows" => self.handle_pop_all_shadows(dl),
+                "backdrop-filter" => self.handle_backdrop_filter(dl, item, &mut info),
+                _ => println!("Skipping unknown item type: {:?}", item),
+            }
+
+            if spatial_id.is_some() {
+                self.spatial_id_stack.pop().unwrap();
+            }
+        }
+    }
+
+    fn next_spatial_key(&mut self) -> SpatialTreeItemKey {
+        let key = SpatialTreeItemKey::new(self.next_spatial_key, 0);
+        self.next_spatial_key += 1;
+        key
+    }
+
+    fn handle_scroll_frame(
+        &mut self,
+        dl: &mut DisplayListBuilder,
+        wrench: &mut Wrench,
+        yaml: &Yaml,
+    ) {
+        let clip_rect = yaml["bounds"]
+            .as_rect()
+            .expect("scroll frame must have a bounds");
+        let content_size = yaml["content-size"].as_size().unwrap_or_else(|| clip_rect.size());
+        let content_rect = LayoutRect::from_origin_and_size(clip_rect.min, content_size);
+        let external_scroll_offset = yaml["external-scroll-offset"].as_vector().unwrap_or_else(LayoutVector2D::zero);
+        let scroll_generation = yaml["scroll-generation"].as_i64().map_or(APZScrollGeneration::default(), |v| v as u64);
+        let has_scroll_linked_effect =
+        yaml["has-scroll-linked-effect"].as_bool().map_or(HasScrollLinkedEffect::default(),
+            |v| if v { HasScrollLinkedEffect::Yes } else { HasScrollLinkedEffect::No }
+        );
+
+        let numeric_id = yaml["id"].as_i64().map(|id| id as u64);
+
+        let external_id = ExternalScrollId(self.next_external_scroll_id, dl.pipeline_id);
+        self.next_external_scroll_id += 1;
+
+        if let Some(vector) = yaml["scroll-offset"].as_vector() {
+            self.scroll_offsets.insert(
+                external_id,
+                vec![SampledScrollOffset {
+                    offset: vector,
+                    generation: APZScrollGeneration::default(),
+                }],
+            );
+        }
+
+        if !yaml["scroll-offsets"].is_badvalue() {
+            let mut offsets = Vec::new();
+            for entry in yaml["scroll-offsets"].as_vec().unwrap() {
+                let offset = entry["offset"].as_vector().unwrap_or(LayoutVector2D::zero());
+                let generation = entry["generation"].as_i64().map_or(APZScrollGeneration::default(), |v| v as u64);
+                offsets.push(SampledScrollOffset { offset, generation });
+            }
+            self.scroll_offsets.insert(external_id, offsets);
+        }
+
+        let clip_to_frame = yaml["clip-to-frame"].as_bool().unwrap_or(false);
+
+        let clip_id = if clip_to_frame {
+            Some(dl.define_clip_rect(
+                self.top_space(),
+                clip_rect,
+            ))
+        } else {
+            None
+        };
+
+        let spatial_id = dl.define_scroll_frame(
+            self.top_space(),
+            external_id,
+            content_rect,
+            clip_rect,
+            external_scroll_offset,
+            scroll_generation,
+            has_scroll_linked_effect,
+            self.next_spatial_key(),
+        );
+        if let Some(numeric_id) = numeric_id {
+            self.add_spatial_id_mapping(numeric_id, spatial_id);
+            if let Some(clip_id) = clip_id {
+                self.add_clip_id_mapping(numeric_id, clip_id);
+            }
+        }
+
+        if let Some(yaml_items) = yaml["items"].as_vec() {
+            self.spatial_id_stack.push(spatial_id);
+            self.add_display_list_items_from_yaml(dl, wrench, yaml_items);
+            self.spatial_id_stack.pop().unwrap();
+        }
+    }
+
+    fn handle_sticky_frame(
+        &mut self,
+        dl: &mut DisplayListBuilder,
+        wrench: &mut Wrench,
+        yaml: &Yaml,
+    ) {
+        let bounds = yaml["bounds"].as_rect().expect("sticky frame must have a bounds");
+        let numeric_id = yaml["id"].as_i64().map(|id| id as u64);
+
+        let real_id = dl.define_sticky_frame(
+            *self.spatial_id_stack.last().unwrap(),
+            bounds,
+            SideOffsets2D::new(
+                yaml["margin-top"].as_f32(),
+                yaml["margin-right"].as_f32(),
+                yaml["margin-bottom"].as_f32(),
+                yaml["margin-left"].as_f32(),
+            ),
+            yaml["vertical-offset-bounds"].as_sticky_offset_bounds(),
+            yaml["horizontal-offset-bounds"].as_sticky_offset_bounds(),
+            yaml["previously-applied-offset"].as_vector().unwrap_or_else(LayoutVector2D::zero),
+            self.next_spatial_key(),
+        );
+
+        if let Some(numeric_id) = numeric_id {
+            self.add_spatial_id_mapping(numeric_id, real_id);
+        }
+
+        if let Some(yaml_items) = yaml["items"].as_vec() {
+            self.spatial_id_stack.push(real_id);
+            self.add_display_list_items_from_yaml(dl, wrench, yaml_items);
+            self.spatial_id_stack.pop().unwrap();
+        }
+    }
+
+    fn resolve_binding<'a>(
+        &'a self,
+        yaml: &'a Yaml,
+    ) -> &'a Yaml {
+        if let Some(keyframes) = &self.keyframes {
+            if let Some(s) = yaml.as_str() {
+                const PREFIX: &str = "key(";
+                const SUFFIX: &str = ")";
+                if let Some(key) = s.strip_prefix(PREFIX).and_then(|s| s.strip_suffix(SUFFIX)) {
+                    return &keyframes[key][self.requested_frame];
+                }
+            }
+        }
+
+        yaml
+    }
+
+    fn resolve_colorf(
+        &self,
+        yaml: &Yaml,
+    ) -> Option<ColorF> {
+        self.resolve_binding(yaml)
+            .as_colorf()
+    }
+
+    fn resolve_rect(
+        &self,
+        yaml: &Yaml,
+    ) -> LayoutRect {
+        self.resolve_binding(yaml)
+            .as_rect()
+            .unwrap_or_else(|| panic!("invalid rect {:?}", yaml))
+    }
+
+    fn resolve_vector(
+        &self,
+        yaml: &Yaml,
+        default: LayoutVector2D,
+    ) -> LayoutVector2D {
+        self.resolve_binding(yaml)
+            .as_vector()
+            .unwrap_or(default)
+    }
+
+    fn handle_push_shadow(
+        &mut self,
+        dl: &mut DisplayListBuilder,
+        yaml: &Yaml,
+        info: &mut CommonItemProperties,
+    ) {
+        let blur_radius = yaml["blur-radius"].as_f32().unwrap_or(0.0);
+        let offset = yaml["offset"].as_vector().unwrap_or_else(LayoutVector2D::zero);
+        let color = yaml["color"].as_colorf().unwrap_or(ColorF::BLACK);
+
+        dl.push_shadow(
+            &SpaceAndClipInfo { spatial_id: info.spatial_id, clip_chain_id: info.clip_chain_id },
+            Shadow {
+                blur_radius,
+                offset,
+                color,
+            },
+            true,
+        );
+    }
+
+    fn handle_pop_all_shadows(&mut self, dl: &mut DisplayListBuilder) {
+        dl.pop_all_shadows();
+    }
+
+    fn handle_clip_chain(&mut self, builder: &mut DisplayListBuilder, yaml: &Yaml) {
+        let numeric_id = yaml["id"].as_i64().expect("clip chains must have an id");
+        let clip_ids: Vec<ClipId> = yaml["clips"]
+            .as_vec_u64()
+            .unwrap_or_default()
+            .iter()
+            .map(|id| self.user_clip_id_map[id])
+            .collect();
+
+        let parent = self.to_clip_chain_id(&yaml["parent"], builder);
+        let real_id = builder.define_clip_chain(parent, clip_ids);
+        self.add_clip_chain_id_mapping(numeric_id as u64, real_id);
+    }
+
+    fn handle_clip(&mut self, dl: &mut DisplayListBuilder, wrench: &mut Wrench, yaml: &Yaml) {
+        let numeric_id = yaml["id"].as_i64();
+        let spatial_id = self.top_space();
+        let complex_clips = yaml["complex"].as_complex_clip_regions();
+        let mut clip_id = None;
+
+        if let Some(clip_rect) = yaml["bounds"].as_rect() {
+            clip_id = Some(dl.define_clip_rect(
+                spatial_id,
+                clip_rect,
+            ));
+        }
+
+        if let Some(image_mask) = self.as_image_mask(&yaml["image-mask"], wrench) {
+            assert!(clip_id.is_none(), "invalid clip definition");
+
+            clip_id = Some(dl.define_clip_image_mask(
+                spatial_id,
+                image_mask,
+                &[],
+                FillRule::Nonzero,
+            ));
+        }
+
+        if !complex_clips.is_empty() {
+            // Only 1 complex clip is supported per clip (todo: change yaml format)
+            assert_eq!(complex_clips.len(), 1);
+            assert!(clip_id.is_none(), "invalid clip definition");
+
+            clip_id = Some(dl.define_clip_rounded_rect(
+                spatial_id,
+                complex_clips[0],
+            ));
+        }
+
+        if let Some(clip_id) = clip_id {
+            if let Some(numeric_id) = numeric_id {
+                self.add_clip_id_mapping(numeric_id as u64, clip_id);
+            }
+        }
+    }
+
+    fn push_reference_frame(
+        &mut self,
+        dl: &mut DisplayListBuilder,
+        default_bounds: impl Fn() -> LayoutRect,
+        yaml: &Yaml,
+    ) -> SpatialId {
+        let bounds = yaml["bounds"].as_rect().unwrap_or_else(default_bounds);
+        let default_transform_origin = LayoutPoint::new(
+            bounds.min.x + bounds.width() * 0.5,
+            bounds.min.y + bounds.height() * 0.5,
+        );
+
+        let transform_style = yaml["transform-style"]
+            .as_transform_style()
+            .unwrap_or(TransformStyle::Flat);
+
+        let transform_origin = yaml["transform-origin"]
+            .as_point()
+            .unwrap_or(default_transform_origin);
+
+        assert!(
+            yaml["transform"].is_badvalue() ||
+            yaml["perspective"].is_badvalue(),
+            "Should have one of either transform or perspective"
+        );
+
+        let perspective_origin = yaml["perspective-origin"]
+            .as_point()
+            .unwrap_or(default_transform_origin);
+
+        let reference_frame_kind = if !yaml["perspective"].is_badvalue() {
+            ReferenceFrameKind::Perspective { scrolling_relative_to: None }
+        } else {
+            ReferenceFrameKind::Transform {
+                is_2d_scale_translation: false,
+                should_snap: false,
+                paired_with_perspective: yaml["paired-with-perspective"].as_bool().unwrap_or(false),
+            }
+        };
+
+        let transform = yaml["transform"]
+            .as_transform(&transform_origin);
+
+        let perspective = match yaml["perspective"].as_f32() {
+            Some(value) if value != 0.0 => {
+                Some(make_perspective(perspective_origin, value as f32))
+            }
+            Some(..) => None,
+            _ => yaml["perspective"].as_matrix4d(),
+        };
+
+        let reference_frame_id = dl.push_reference_frame(
+            bounds.min,
+            *self.spatial_id_stack.last().unwrap(),
+            transform_style,
+            transform.or(perspective).unwrap_or_default().into(),
+            reference_frame_kind,
+            self.next_spatial_key(),
+        );
+
+        let numeric_id = yaml["id"].as_i64();
+        if let Some(numeric_id) = numeric_id {
+            self.add_spatial_id_mapping(numeric_id as u64, reference_frame_id);
+        }
+
+        reference_frame_id
+    }
+
+    fn handle_reference_frame(
+        &mut self,
+        dl: &mut DisplayListBuilder,
+        wrench: &mut Wrench,
+        yaml: &Yaml,
+    ) {
+        let default_bounds = || LayoutRect::from_size(wrench.window_size_f32());
+        let real_id = self.push_reference_frame(dl, default_bounds, yaml);
+        self.spatial_id_stack.push(real_id);
+
+        if let Some(yaml_items) = yaml["items"].as_vec() {
+            self.add_display_list_items_from_yaml(dl, wrench, yaml_items);
+        }
+
+        self.spatial_id_stack.pop().unwrap();
+        dl.pop_reference_frame();
+    }
+
+    fn push_computed_frame(
+        &mut self,
+        dl: &mut DisplayListBuilder,
+        default_bounds: impl Fn() -> LayoutRect,
+        yaml: &Yaml,
+    ) -> SpatialId {
+        let bounds = yaml["bounds"].as_rect().unwrap_or_else(default_bounds);
+
+        let scale_from = yaml["scale-from"].as_size();
+        let vertical_flip = yaml["vertical-flip"].as_bool().unwrap_or(false);
+        let rotation = yaml["rotation"].as_rotation().unwrap_or(Rotation::Degree0);
+
+        let reference_frame_id = dl.push_computed_frame(
+            bounds.min,
+            *self.spatial_id_stack.last().unwrap(),
+            scale_from,
+            vertical_flip,
+            rotation,
+            self.next_spatial_key(),
+        );
+
+        let numeric_id = yaml["id"].as_i64();
+        if let Some(numeric_id) = numeric_id {
+            self.add_spatial_id_mapping(numeric_id as u64, reference_frame_id);
+        }
+
+        reference_frame_id
+    }
+
+    fn handle_computed_frame(
+        &mut self,
+        dl: &mut DisplayListBuilder,
+        wrench: &mut Wrench,
+        yaml: &Yaml,
+    ) {
+        let default_bounds = || LayoutRect::from_size(wrench.window_size_f32());
+        let real_id = self.push_computed_frame(dl, default_bounds, yaml);
+        self.spatial_id_stack.push(real_id);
+
+        if let Some(yaml_items) = yaml["items"].as_vec() {
+            self.add_display_list_items_from_yaml(dl, wrench, yaml_items);
+        }
+
+        self.spatial_id_stack.pop().unwrap();
+        dl.pop_reference_frame();
+    }
+
+    fn add_stacking_context_from_yaml(
+        &mut self,
+        dl: &mut DisplayListBuilder,
+        wrench: &mut Wrench,
+        yaml: &Yaml,
+        IsRoot(is_root): IsRoot,
+        info: &mut CommonItemProperties,
+    ) {
+        let default_bounds = || LayoutRect::from_size(wrench.window_size_f32());
+        let mut bounds = yaml["bounds"].as_rect().unwrap_or_else(default_bounds);
+
+        let pushed_reference_frame =
+            if !yaml["transform"].is_badvalue() || !yaml["perspective"].is_badvalue() {
+                let reference_frame_id = self.push_reference_frame(dl, default_bounds, yaml);
+                self.spatial_id_stack.push(reference_frame_id);
+                bounds.max -= bounds.min.to_vector();
+                bounds.min = LayoutPoint::zero();
+                true
+            } else {
+                false
+            };
+
+        let clip_chain_id = self.to_clip_chain_id(&yaml["clip-chain"], dl);
+
+        let transform_style = yaml["transform-style"]
+            .as_transform_style()
+            .unwrap_or(TransformStyle::Flat);
+        let mix_blend_mode = yaml["mix-blend-mode"]
+            .as_mix_blend_mode()
+            .unwrap_or(MixBlendMode::Normal);
+        let raster_space = yaml["raster-space"]
+            .as_raster_space()
+            .unwrap_or(RasterSpace::Screen);
+        let is_blend_container = yaml["blend-container"].as_bool().unwrap_or(false);
+        let wraps_backdrop_filter = yaml["wraps-backdrop-filter"].as_bool().unwrap_or(false);
+
+        if is_root {
+            if let Some(vector) = yaml["scroll-offset"].as_vector() {
+                let external_id = ExternalScrollId(0, dl.pipeline_id);
+                self.scroll_offsets.insert(
+                    external_id,
+                    vec![SampledScrollOffset {
+                        offset: vector,
+                        generation: APZScrollGeneration::default(),
+                    }],
+                );
+            }
+        }
+
+        let filters = yaml["filters"].as_vec_filter_op().unwrap_or_default();
+        let filter_datas = yaml["filter-datas"].as_vec_filter_data().unwrap_or_default();
+        let filter_primitives = yaml["filter-primitives"].as_vec_filter_primitive().unwrap_or_default();
+
+        let mut flags = StackingContextFlags::empty();
+        flags.set(StackingContextFlags::IS_BLEND_CONTAINER, is_blend_container);
+        flags.set(StackingContextFlags::WRAPS_BACKDROP_FILTER, wraps_backdrop_filter);
+
+        dl.push_stacking_context(
+            bounds.min,
+            *self.spatial_id_stack.last().unwrap(),
+            info.flags,
+            clip_chain_id,
+            transform_style,
+            mix_blend_mode,
+            &filters,
+            &filter_datas,
+            &filter_primitives,
+            raster_space,
+            flags,
+        );
+
+        if let Some(yaml_items) = yaml["items"].as_vec() {
+            self.add_display_list_items_from_yaml(dl, wrench, yaml_items);
+        }
+
+        dl.pop_stacking_context();
+
+        if pushed_reference_frame {
+            self.spatial_id_stack.pop().unwrap();
+            dl.pop_reference_frame();
+        }
+    }
+
+    fn handle_backdrop_filter(
+        &mut self,
+        dl: &mut DisplayListBuilder,
+        item: &Yaml,
+        info: &mut CommonItemProperties,
+    ) {
+        info.clip_rect = try_intersect!(
+            self.resolve_rect(&item["bounds"]),
+            &info.clip_rect
+        );
+
+        let filters = item["filters"].as_vec_filter_op().unwrap_or_default();
+        let filter_datas = item["filter-datas"].as_vec_filter_data().unwrap_or_default();
+        let filter_primitives = item["filter-primitives"].as_vec_filter_primitive().unwrap_or_default();
+
+        dl.push_backdrop_filter(
+            info,
+            &filters,
+            &filter_datas,
+            &filter_primitives,
+        );
+    }
+}
+
+impl WrenchThing for YamlFrameReader {
+    fn do_frame(&mut self, wrench: &mut Wrench) -> u32 {
+        let mut should_build_yaml = false;
+
+        // If YAML isn't read yet, or watching source file, reload from disk.
+        if self.yaml_string.is_empty() || self.watch_source {
+            self.yaml_string = std::fs::read_to_string(&self.yaml_path)
+                 .unwrap_or_else(|_| panic!("YAML '{:?}' doesn't exist", self.yaml_path));
+            should_build_yaml = true;
+        }
+
+        // Evaluate conditions that require parsing the YAML.
+        if self.built_frame != self.requested_frame {
+            // Requested frame has changed
+            should_build_yaml = true;
+        }
+
+        // Build the DL from YAML if required
+        if should_build_yaml {
+            self.build(wrench);
+        }
+
+        // Determine whether to send a new DL, or just refresh.
+        if should_build_yaml || wrench.should_rebuild_display_lists() {
+            wrench.begin_frame();
+            wrench.send_lists(
+                self.frame_count,
+                self.display_lists.clone(),
+                &self.scroll_offsets,
+            );
+        } else {
+            wrench.refresh();
+        }
+
+        self.frame_count += 1;
+        self.frame_count
+    }
+
+    fn next_frame(&mut self) {
+        let mut max_frame_count = 0;
+        if let Some(ref keyframes) = self.keyframes {
+            for (_, values) in keyframes.as_hash().unwrap() {
+                max_frame_count = max_frame_count.max(values.as_vec().unwrap().len());
+            }
+        }
+        if self.requested_frame + 1 < max_frame_count {
+            self.requested_frame += 1;
+        }
+    }
+
+    fn prev_frame(&mut self) {
+        if self.requested_frame > 0 {
+            self.requested_frame -= 1;
+        }
+    }
+}