Adding upstream version 110.0.1.upstream/110.0.1upstream

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

1 files changed, 1470 insertions, 0 deletions

diff --git a/gfx/wr/webrender/src/prepare.rs b/gfx/wr/webrender/src/prepare.rs
new file mode 100644
index 0000000000..cca3005023
--- /dev/null
+++ b/gfx/wr/webrender/src/prepare.rs
@@ -0,0 +1,1470 @@
+/* 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/. */
+
+//! # Prepare pass
+//!
+//! TODO: document this!
+
+use std::cmp;
+use api::{PremultipliedColorF, PropertyBinding};
+use api::{BoxShadowClipMode, BorderStyle, ClipMode};
+use api::units::*;
+use euclid::Scale;
+use smallvec::SmallVec;
+use crate::command_buffer::PrimitiveCommand;
+use crate::image_tiling::{self, Repetition};
+use crate::border::{get_max_scale_for_border, build_border_instances};
+use crate::clip::{ClipStore};
+use crate::spatial_tree::{SpatialNodeIndex, SpatialTree};
+use crate::clip::{ClipDataStore, ClipNodeFlags, ClipChainInstance, ClipItemKind};
+use crate::frame_builder::{FrameBuildingContext, FrameBuildingState, PictureContext, PictureState};
+use crate::gpu_cache::{GpuCacheHandle, GpuDataRequest};
+use crate::gpu_types::{BrushFlags};
+use crate::internal_types::{FastHashMap, PlaneSplitAnchor};
+use crate::picture::{PicturePrimitive, SliceId, ClusterFlags};
+use crate::picture::{PrimitiveList, PrimitiveCluster, SurfaceIndex, TileCacheInstance, SubpixelMode, Picture3DContext};
+use crate::prim_store::line_dec::MAX_LINE_DECORATION_RESOLUTION;
+use crate::prim_store::*;
+use crate::prim_store::gradient::GradientGpuBlockBuilder;
+use crate::render_backend::DataStores;
+use crate::render_task_graph::RenderTaskId;
+use crate::render_task_cache::RenderTaskCacheKeyKind;
+use crate::render_task_cache::{RenderTaskCacheKey, to_cache_size, RenderTaskParent};
+use crate::render_task::{RenderTaskKind, RenderTask};
+use crate::segment::SegmentBuilder;
+use crate::util::{clamp_to_scale_factor, pack_as_float};
+use crate::visibility::{compute_conservative_visible_rect, PrimitiveVisibility, VisibilityState};
+
+
+const MAX_MASK_SIZE: f32 = 4096.0;
+
+const MIN_BRUSH_SPLIT_AREA: f32 = 128.0 * 128.0;
+
+
+pub fn prepare_primitives(
+    store: &mut PrimitiveStore,
+    prim_list: &mut PrimitiveList,
+    pic_context: &PictureContext,
+    pic_state: &mut PictureState,
+    frame_context: &FrameBuildingContext,
+    frame_state: &mut FrameBuildingState,
+    data_stores: &mut DataStores,
+    scratch: &mut PrimitiveScratchBuffer,
+    tile_caches: &mut FastHashMap<SliceId, Box<TileCacheInstance>>,
+    prim_instances: &mut Vec<PrimitiveInstance>,
+) {
+    profile_scope!("prepare_primitives");
+    for cluster in &mut prim_list.clusters {
+        if !cluster.flags.contains(ClusterFlags::IS_VISIBLE) {
+            continue;
+        }
+        profile_scope!("cluster");
+        pic_state.map_local_to_pic.set_target_spatial_node(
+            cluster.spatial_node_index,
+            frame_context.spatial_tree,
+        );
+
+        for prim_instance_index in cluster.prim_range() {
+            if frame_state.surface_builder.is_prim_visible_and_in_dirty_region(&prim_instances[prim_instance_index].vis) {
+
+                let plane_split_anchor = PlaneSplitAnchor::new(
+                    cluster.spatial_node_index,
+                    PrimitiveInstanceIndex(prim_instance_index as u32),
+                );
+
+                if let Some(ref prim_cmd) = prepare_prim_for_render(
+                    store,
+                    prim_instance_index,
+                    cluster,
+                    pic_context,
+                    pic_state,
+                    frame_context,
+                    frame_state,
+                    plane_split_anchor,
+                    data_stores,
+                    scratch,
+                    tile_caches,
+                    prim_instances,
+                ) {
+                    frame_state.surface_builder.push_prim(
+                        prim_cmd,
+                        cluster.spatial_node_index,
+                        &prim_instances[prim_instance_index].vis,
+                        frame_state.cmd_buffers,
+                    );
+
+                    frame_state.num_visible_primitives += 1;
+                    continue;
+                }
+            }
+
+            // TODO(gw): Technically no need to clear visibility here, since from this point it
+            //           only matters if it got added to a command buffer. Kept here for now to
+            //           make debugging simpler, but perhaps we can remove / tidy this up.
+            prim_instances[prim_instance_index].clear_visibility();
+        }
+    }
+}
+
+fn prepare_prim_for_render(
+    store: &mut PrimitiveStore,
+    prim_instance_index: usize,
+    cluster: &mut PrimitiveCluster,
+    pic_context: &PictureContext,
+    pic_state: &mut PictureState,
+    frame_context: &FrameBuildingContext,
+    frame_state: &mut FrameBuildingState,
+    plane_split_anchor: PlaneSplitAnchor,
+    data_stores: &mut DataStores,
+    scratch: &mut PrimitiveScratchBuffer,
+    tile_caches: &mut FastHashMap<SliceId, Box<TileCacheInstance>>,
+    prim_instances: &mut Vec<PrimitiveInstance>,
+) -> Option<PrimitiveCommand> {
+    profile_scope!("prepare_prim_for_render");
+
+    // If we have dependencies, we need to prepare them first, in order
+    // to know the actual rect of this primitive.
+    // For example, scrolling may affect the location of an item in
+    // local space, which may force us to render this item on a larger
+    // picture target, if being composited.
+    let mut is_passthrough = false;
+    if let PrimitiveInstanceKind::Picture { pic_index, .. } = prim_instances[prim_instance_index].kind {
+        let pic = &mut store.pictures[pic_index.0];
+
+        // TODO(gw): Plan to remove pictures with no composite mode, so that we don't need
+        //           to special case for pass through pictures.
+        is_passthrough = pic.composite_mode.is_none();
+
+        match pic.take_context(
+            pic_index,
+            Some(pic_context.surface_index),
+            pic_context.subpixel_mode,
+            frame_state,
+            frame_context,
+            scratch,
+            tile_caches,
+        ) {
+            Some((pic_context_for_children, mut pic_state_for_children, mut prim_list)) => {
+                prepare_primitives(
+                    store,
+                    &mut prim_list,
+                    &pic_context_for_children,
+                    &mut pic_state_for_children,
+                    frame_context,
+                    frame_state,
+                    data_stores,
+                    scratch,
+                    tile_caches,
+                    prim_instances,
+                );
+
+                // Restore the dependencies (borrow check dance)
+                store.pictures[pic_context_for_children.pic_index.0]
+                    .restore_context(
+                        pic_context_for_children.pic_index,
+                        prim_list,
+                        pic_context_for_children,
+                        prim_instances,
+                        frame_context,
+                        frame_state,
+                    );
+            }
+            None => {
+                return None;
+            }
+        }
+    }
+
+    let prim_instance = &mut prim_instances[prim_instance_index];
+
+    if !is_passthrough {
+        let prim_rect = data_stores.get_local_prim_rect(
+            prim_instance,
+            &store.pictures,
+            frame_state.surfaces,
+        );
+
+        if !update_clip_task(
+            prim_instance,
+            &prim_rect.min,
+            cluster.spatial_node_index,
+            pic_context.raster_spatial_node_index,
+            pic_context,
+            pic_state,
+            frame_context,
+            frame_state,
+            store,
+            data_stores,
+            scratch,
+        ) {
+            return None;
+        }
+    }
+
+    Some(prepare_interned_prim_for_render(
+        store,
+        PrimitiveInstanceIndex(prim_instance_index as u32),
+        prim_instance,
+        cluster,
+        plane_split_anchor,
+        pic_context,
+        frame_context,
+        frame_state,
+        data_stores,
+        scratch,
+    ))
+}
+
+/// Prepare an interned primitive for rendering, by requesting
+/// resources, render tasks etc. This is equivalent to the
+/// prepare_prim_for_render_inner call for old style primitives.
+fn prepare_interned_prim_for_render(
+    store: &mut PrimitiveStore,
+    prim_instance_index: PrimitiveInstanceIndex,
+    prim_instance: &mut PrimitiveInstance,
+    cluster: &mut PrimitiveCluster,
+    plane_split_anchor: PlaneSplitAnchor,
+    pic_context: &PictureContext,
+    frame_context: &FrameBuildingContext,
+    frame_state: &mut FrameBuildingState,
+    data_stores: &mut DataStores,
+    scratch: &mut PrimitiveScratchBuffer,
+) -> PrimitiveCommand {
+    let prim_spatial_node_index = cluster.spatial_node_index;
+    let device_pixel_scale = frame_state.surfaces[pic_context.surface_index.0].device_pixel_scale;
+    let mut prim_cmd = None;
+
+    match &mut prim_instance.kind {
+        PrimitiveInstanceKind::LineDecoration { data_handle, ref mut render_task, .. } => {
+            profile_scope!("LineDecoration");
+            let prim_data = &mut data_stores.line_decoration[*data_handle];
+            let common_data = &mut prim_data.common;
+            let line_dec_data = &mut prim_data.kind;
+
+            // Update the template this instane references, which may refresh the GPU
+            // cache with any shared template data.
+            line_dec_data.update(common_data, frame_state);
+
+            // Work out the device pixel size to be used to cache this line decoration.
+
+            // If we have a cache key, it's a wavy / dashed / dotted line. Otherwise, it's
+            // a simple solid line.
+            if let Some(cache_key) = line_dec_data.cache_key.as_ref() {
+                // TODO(gw): These scale factors don't do a great job if the world transform
+                //           contains perspective
+                let scale = frame_context
+                    .spatial_tree
+                    .get_world_transform(prim_spatial_node_index)
+                    .scale_factors();
+
+                // Scale factors are normalized to a power of 2 to reduce the number of
+                // resolution changes.
+                // For frames with a changing scale transform round scale factors up to
+                // nearest power-of-2 boundary so that we don't keep having to redraw
+                // the content as it scales up and down. Rounding up to nearest
+                // power-of-2 boundary ensures we never scale up, only down --- avoiding
+                // jaggies. It also ensures we never scale down by more than a factor of
+                // 2, avoiding bad downscaling quality.
+                let scale_width = clamp_to_scale_factor(scale.0, false);
+                let scale_height = clamp_to_scale_factor(scale.1, false);
+                // Pick the maximum dimension as scale
+                let world_scale = LayoutToWorldScale::new(scale_width.max(scale_height));
+
+                let scale_factor = world_scale * Scale::new(1.0);
+                let mut task_size = (LayoutSize::from_au(cache_key.size) * scale_factor).ceil().to_i32();
+                if task_size.width > MAX_LINE_DECORATION_RESOLUTION as i32 ||
+                   task_size.height > MAX_LINE_DECORATION_RESOLUTION as i32 {
+                     let max_extent = cmp::max(task_size.width, task_size.height);
+                     let task_scale_factor = Scale::new(MAX_LINE_DECORATION_RESOLUTION as f32 / max_extent as f32);
+                     task_size = (LayoutSize::from_au(cache_key.size) * scale_factor * task_scale_factor)
+                                    .ceil().to_i32();
+                }
+
+                // It's plausible, due to float accuracy issues that the line decoration may be considered
+                // visible even if the scale factors are ~0. However, the render task allocation below requires
+                // that the size of the task is > 0. To work around this, ensure that the task size is at least
+                // 1x1 pixels
+                task_size.width = task_size.width.max(1);
+                task_size.height = task_size.height.max(1);
+
+                // Request a pre-rendered image task.
+                // TODO(gw): This match is a bit untidy, but it should disappear completely
+                //           once the prepare_prims and batching are unified. When that
+                //           happens, we can use the cache handle immediately, and not need
+                //           to temporarily store it in the primitive instance.
+                *render_task = Some(frame_state.resource_cache.request_render_task(
+                    RenderTaskCacheKey {
+                        size: task_size,
+                        kind: RenderTaskCacheKeyKind::LineDecoration(cache_key.clone()),
+                    },
+                    frame_state.gpu_cache,
+                    frame_state.frame_gpu_data,
+                    frame_state.rg_builder,
+                    None,
+                    false,
+                    RenderTaskParent::Surface(pic_context.surface_index),
+                    &mut frame_state.surface_builder,
+                    |rg_builder, _| {
+                        rg_builder.add().init(RenderTask::new_dynamic(
+                            task_size,
+                            RenderTaskKind::new_line_decoration(
+                                cache_key.style,
+                                cache_key.orientation,
+                                cache_key.wavy_line_thickness.to_f32_px(),
+                                LayoutSize::from_au(cache_key.size),
+                            ),
+                        ))
+                    }
+                ));
+            }
+        }
+        PrimitiveInstanceKind::TextRun { run_index, data_handle, .. } => {
+            profile_scope!("TextRun");
+            let prim_data = &mut data_stores.text_run[*data_handle];
+            let run = &mut store.text_runs[*run_index];
+
+            prim_data.common.may_need_repetition = false;
+
+            // The glyph transform has to match `glyph_transform` in "ps_text_run" shader.
+            // It's relative to the rasterizing space of a glyph.
+            let transform = frame_context.spatial_tree
+                .get_relative_transform(
+                    prim_spatial_node_index,
+                    pic_context.raster_spatial_node_index,
+                )
+                .into_fast_transform();
+            let prim_offset = prim_data.common.prim_rect.min.to_vector() - run.reference_frame_relative_offset;
+
+            let surface = &frame_state.surfaces[pic_context.surface_index.0];
+
+            // If subpixel AA is disabled due to the backing surface the glyphs
+            // are being drawn onto, disable it (unless we are using the
+            // specifial subpixel mode that estimates background color).
+            let allow_subpixel = match prim_instance.vis.state {
+                VisibilityState::Culled |
+                VisibilityState::Unset |
+                VisibilityState::PassThrough => {
+                    panic!("bug: invalid visibility state");
+                }
+                VisibilityState::Visible { sub_slice_index, .. } => {
+                    // For now, we only allow subpixel AA on primary sub-slices. In future we
+                    // may support other sub-slices if we find content that does this.
+                    if sub_slice_index.is_primary() {
+                        match pic_context.subpixel_mode {
+                            SubpixelMode::Allow => true,
+                            SubpixelMode::Deny => false,
+                            SubpixelMode::Conditional { allowed_rect } => {
+                                // Conditional mode allows subpixel AA to be enabled for this
+                                // text run, so long as it's inside the allowed rect.
+                                allowed_rect.contains_box(&prim_instance.vis.clip_chain.pic_coverage_rect)
+                            }
+                        }
+                    } else {
+                        false
+                    }
+                }
+            };
+
+            run.request_resources(
+                prim_offset,
+                &prim_data.font,
+                &prim_data.glyphs,
+                &transform.to_transform().with_destination::<_>(),
+                surface,
+                prim_spatial_node_index,
+                allow_subpixel,
+                frame_context.fb_config.low_quality_pinch_zoom,
+                frame_state.resource_cache,
+                frame_state.gpu_cache,
+                frame_context.spatial_tree,
+                scratch,
+            );
+
+            // Update the template this instane references, which may refresh the GPU
+            // cache with any shared template data.
+            prim_data.update(frame_state);
+        }
+        PrimitiveInstanceKind::Clear { data_handle, .. } => {
+            profile_scope!("Clear");
+            let prim_data = &mut data_stores.prim[*data_handle];
+
+            prim_data.common.may_need_repetition = false;
+
+            // Update the template this instane references, which may refresh the GPU
+            // cache with any shared template data.
+            prim_data.update(frame_state, frame_context.scene_properties);
+        }
+        PrimitiveInstanceKind::NormalBorder { data_handle, ref mut render_task_ids, .. } => {
+            profile_scope!("NormalBorder");
+            let prim_data = &mut data_stores.normal_border[*data_handle];
+            let common_data = &mut prim_data.common;
+            let border_data = &mut prim_data.kind;
+
+            common_data.may_need_repetition =
+                matches!(border_data.border.top.style, BorderStyle::Dotted | BorderStyle::Dashed) ||
+                matches!(border_data.border.right.style, BorderStyle::Dotted | BorderStyle::Dashed) ||
+                matches!(border_data.border.bottom.style, BorderStyle::Dotted | BorderStyle::Dashed) ||
+                matches!(border_data.border.left.style, BorderStyle::Dotted | BorderStyle::Dashed);
+
+
+            // Update the template this instance references, which may refresh the GPU
+            // cache with any shared template data.
+            border_data.update(common_data, frame_state);
+
+            // TODO(gw): For now, the scale factors to rasterize borders at are
+            //           based on the true world transform of the primitive. When
+            //           raster roots with local scale are supported in future,
+            //           that will need to be accounted for here.
+            let scale = frame_context
+                .spatial_tree
+                .get_world_transform(prim_spatial_node_index)
+                .scale_factors();
+
+            // Scale factors are normalized to a power of 2 to reduce the number of
+            // resolution changes.
+            // For frames with a changing scale transform round scale factors up to
+            // nearest power-of-2 boundary so that we don't keep having to redraw
+            // the content as it scales up and down. Rounding up to nearest
+            // power-of-2 boundary ensures we never scale up, only down --- avoiding
+            // jaggies. It also ensures we never scale down by more than a factor of
+            // 2, avoiding bad downscaling quality.
+            let scale_width = clamp_to_scale_factor(scale.0, false);
+            let scale_height = clamp_to_scale_factor(scale.1, false);
+            // Pick the maximum dimension as scale
+            let world_scale = LayoutToWorldScale::new(scale_width.max(scale_height));
+            let mut scale = world_scale * device_pixel_scale;
+            let max_scale = get_max_scale_for_border(border_data);
+            scale.0 = scale.0.min(max_scale.0);
+
+            // For each edge and corner, request the render task by content key
+            // from the render task cache. This ensures that the render task for
+            // this segment will be available for batching later in the frame.
+            let mut handles: SmallVec<[RenderTaskId; 8]> = SmallVec::new();
+
+            for segment in &border_data.border_segments {
+                // Update the cache key device size based on requested scale.
+                let cache_size = to_cache_size(segment.local_task_size, &mut scale);
+                let cache_key = RenderTaskCacheKey {
+                    kind: RenderTaskCacheKeyKind::BorderSegment(segment.cache_key.clone()),
+                    size: cache_size,
+                };
+
+                handles.push(frame_state.resource_cache.request_render_task(
+                    cache_key,
+                    frame_state.gpu_cache,
+                    frame_state.frame_gpu_data,
+                    frame_state.rg_builder,
+                    None,
+                    false,          // TODO(gw): We don't calculate opacity for borders yet!
+                    RenderTaskParent::Surface(pic_context.surface_index),
+                    &mut frame_state.surface_builder,
+                    |rg_builder, _| {
+                        rg_builder.add().init(RenderTask::new_dynamic(
+                            cache_size,
+                            RenderTaskKind::new_border_segment(
+                                build_border_instances(
+                                    &segment.cache_key,
+                                    cache_size,
+                                    &border_data.border,
+                                    scale,
+                                )
+                            ),
+                        ))
+                    }
+                ));
+            }
+
+            *render_task_ids = scratch
+                .border_cache_handles
+                .extend(handles);
+        }
+        PrimitiveInstanceKind::ImageBorder { data_handle, .. } => {
+            profile_scope!("ImageBorder");
+            let prim_data = &mut data_stores.image_border[*data_handle];
+
+            // TODO: get access to the ninepatch and to check whether we need support
+            // for repetitions in the shader.
+
+            // Update the template this instance references, which may refresh the GPU
+            // cache with any shared template data.
+            prim_data.kind.update(
+                &mut prim_data.common,
+                frame_state
+            );
+        }
+        PrimitiveInstanceKind::Rectangle { data_handle, segment_instance_index, color_binding_index, .. } => {
+            profile_scope!("Rectangle");
+            let prim_data = &mut data_stores.prim[*data_handle];
+            prim_data.common.may_need_repetition = false;
+
+            if *color_binding_index != ColorBindingIndex::INVALID {
+                match store.color_bindings[*color_binding_index] {
+                    PropertyBinding::Binding(..) => {
+                        // We explicitly invalidate the gpu cache
+                        // if the color is animating.
+                        let gpu_cache_handle =
+                            if *segment_instance_index == SegmentInstanceIndex::INVALID {
+                                None
+                            } else if *segment_instance_index == SegmentInstanceIndex::UNUSED {
+                                Some(&prim_data.common.gpu_cache_handle)
+                            } else {
+                                Some(&scratch.segment_instances[*segment_instance_index].gpu_cache_handle)
+                            };
+                        if let Some(gpu_cache_handle) = gpu_cache_handle {
+                            frame_state.gpu_cache.invalidate(gpu_cache_handle);
+                        }
+                    }
+                    PropertyBinding::Value(..) => {},
+                }
+            }
+
+            // Update the template this instane references, which may refresh the GPU
+            // cache with any shared template data.
+            prim_data.update(
+                frame_state,
+                frame_context.scene_properties,
+            );
+
+            write_segment(
+                *segment_instance_index,
+                frame_state,
+                &mut scratch.segments,
+                &mut scratch.segment_instances,
+                |request| {
+                    prim_data.kind.write_prim_gpu_blocks(
+                        request,
+                        frame_context.scene_properties,
+                    );
+                }
+            );
+        }
+        PrimitiveInstanceKind::YuvImage { data_handle, segment_instance_index, .. } => {
+            profile_scope!("YuvImage");
+            let prim_data = &mut data_stores.yuv_image[*data_handle];
+            let common_data = &mut prim_data.common;
+            let yuv_image_data = &mut prim_data.kind;
+
+            common_data.may_need_repetition = false;
+
+            // Update the template this instane references, which may refresh the GPU
+            // cache with any shared template data.
+            yuv_image_data.update(common_data, frame_state);
+
+            write_segment(
+                *segment_instance_index,
+                frame_state,
+                &mut scratch.segments,
+                &mut scratch.segment_instances,
+                |request| {
+                    yuv_image_data.write_prim_gpu_blocks(request);
+                }
+            );
+        }
+        PrimitiveInstanceKind::Image { data_handle, image_instance_index, .. } => {
+            profile_scope!("Image");
+
+            let prim_data = &mut data_stores.image[*data_handle];
+            let common_data = &mut prim_data.common;
+            let image_data = &mut prim_data.kind;
+            let image_instance = &mut store.images[*image_instance_index];
+
+            // Update the template this instance references, which may refresh the GPU
+            // cache with any shared template data.
+            image_data.update(
+                common_data,
+                image_instance,
+                pic_context.surface_index,
+                prim_spatial_node_index,
+                frame_state,
+                frame_context,
+                &mut prim_instance.vis,
+            );
+
+            write_segment(
+                image_instance.segment_instance_index,
+                frame_state,
+                &mut scratch.segments,
+                &mut scratch.segment_instances,
+                |request| {
+                    image_data.write_prim_gpu_blocks(request);
+                },
+            );
+        }
+        PrimitiveInstanceKind::LinearGradient { data_handle, ref mut visible_tiles_range, .. } => {
+            profile_scope!("LinearGradient");
+            let prim_data = &mut data_stores.linear_grad[*data_handle];
+
+            // Update the template this instane references, which may refresh the GPU
+            // cache with any shared template data.
+            prim_data.update(frame_state, pic_context.surface_index);
+
+            if prim_data.stretch_size.width >= prim_data.common.prim_rect.width() &&
+                prim_data.stretch_size.height >= prim_data.common.prim_rect.height() {
+
+                prim_data.common.may_need_repetition = false;
+            }
+
+            if prim_data.tile_spacing != LayoutSize::zero() {
+                // We are performing the decomposition on the CPU here, no need to
+                // have it in the shader.
+                prim_data.common.may_need_repetition = false;
+
+                *visible_tiles_range = decompose_repeated_gradient(
+                    &prim_instance.vis,
+                    &prim_data.common.prim_rect,
+                    prim_spatial_node_index,
+                    &prim_data.stretch_size,
+                    &prim_data.tile_spacing,
+                    frame_state,
+                    &mut scratch.gradient_tiles,
+                    &frame_context.spatial_tree,
+                    Some(&mut |_, mut request| {
+                        request.push([
+                            prim_data.start_point.x,
+                            prim_data.start_point.y,
+                            prim_data.end_point.x,
+                            prim_data.end_point.y,
+                        ]);
+                        request.push([
+                            pack_as_float(prim_data.extend_mode as u32),
+                            prim_data.stretch_size.width,
+                            prim_data.stretch_size.height,
+                            0.0,
+                        ]);
+                    }),
+                );
+
+                if visible_tiles_range.is_empty() {
+                    prim_instance.clear_visibility();
+                }
+            }
+
+            let stops_address = GradientGpuBlockBuilder::build(
+                prim_data.reverse_stops,
+                frame_state.frame_gpu_data,
+                &prim_data.stops,
+            );
+
+            // TODO(gw): Consider whether it's worth doing segment building
+            //           for gradient primitives.
+
+            prim_cmd = Some(PrimitiveCommand::instance(prim_instance_index, stops_address));
+        }
+        PrimitiveInstanceKind::CachedLinearGradient { data_handle, ref mut visible_tiles_range, .. } => {
+            profile_scope!("CachedLinearGradient");
+            let prim_data = &mut data_stores.linear_grad[*data_handle];
+            prim_data.common.may_need_repetition = prim_data.stretch_size.width < prim_data.common.prim_rect.width()
+                || prim_data.stretch_size.height < prim_data.common.prim_rect.height();
+
+            // Update the template this instance references, which may refresh the GPU
+            // cache with any shared template data.
+            prim_data.update(frame_state, pic_context.surface_index);
+
+            if prim_data.tile_spacing != LayoutSize::zero() {
+                prim_data.common.may_need_repetition = false;
+
+                *visible_tiles_range = decompose_repeated_gradient(
+                    &prim_instance.vis,
+                    &prim_data.common.prim_rect,
+                    prim_spatial_node_index,
+                    &prim_data.stretch_size,
+                    &prim_data.tile_spacing,
+                    frame_state,
+                    &mut scratch.gradient_tiles,
+                    &frame_context.spatial_tree,
+                    None,
+                );
+
+                if visible_tiles_range.is_empty() {
+                    prim_instance.clear_visibility();
+                }
+            }
+        }
+        PrimitiveInstanceKind::RadialGradient { data_handle, ref mut visible_tiles_range, .. } => {
+            profile_scope!("RadialGradient");
+            let prim_data = &mut data_stores.radial_grad[*data_handle];
+
+            prim_data.common.may_need_repetition = prim_data.stretch_size.width < prim_data.common.prim_rect.width()
+                || prim_data.stretch_size.height < prim_data.common.prim_rect.height();
+
+            // Update the template this instane references, which may refresh the GPU
+            // cache with any shared template data.
+            prim_data.update(frame_state, pic_context.surface_index);
+
+            if prim_data.tile_spacing != LayoutSize::zero() {
+                prim_data.common.may_need_repetition = false;
+
+                *visible_tiles_range = decompose_repeated_gradient(
+                    &prim_instance.vis,
+                    &prim_data.common.prim_rect,
+                    prim_spatial_node_index,
+                    &prim_data.stretch_size,
+                    &prim_data.tile_spacing,
+                    frame_state,
+                    &mut scratch.gradient_tiles,
+                    &frame_context.spatial_tree,
+                    None,
+                );
+
+                if visible_tiles_range.is_empty() {
+                    prim_instance.clear_visibility();
+                }
+            }
+
+            // TODO(gw): Consider whether it's worth doing segment building
+            //           for gradient primitives.
+        }
+        PrimitiveInstanceKind::ConicGradient { data_handle, ref mut visible_tiles_range, .. } => {
+            profile_scope!("ConicGradient");
+            let prim_data = &mut data_stores.conic_grad[*data_handle];
+
+            prim_data.common.may_need_repetition = prim_data.stretch_size.width < prim_data.common.prim_rect.width()
+                || prim_data.stretch_size.height < prim_data.common.prim_rect.height();
+
+            // Update the template this instane references, which may refresh the GPU
+            // cache with any shared template data.
+            prim_data.update(frame_state, pic_context.surface_index);
+
+            if prim_data.tile_spacing != LayoutSize::zero() {
+                prim_data.common.may_need_repetition = false;
+
+                *visible_tiles_range = decompose_repeated_gradient(
+                    &prim_instance.vis,
+                    &prim_data.common.prim_rect,
+                    prim_spatial_node_index,
+                    &prim_data.stretch_size,
+                    &prim_data.tile_spacing,
+                    frame_state,
+                    &mut scratch.gradient_tiles,
+                    &frame_context.spatial_tree,
+                    None,
+                );
+
+                if visible_tiles_range.is_empty() {
+                    prim_instance.clear_visibility();
+                }
+            }
+
+            // TODO(gw): Consider whether it's worth doing segment building
+            //           for gradient primitives.
+        }
+        PrimitiveInstanceKind::Picture { pic_index, segment_instance_index, .. } => {
+            profile_scope!("Picture");
+            let pic = &mut store.pictures[pic_index.0];
+
+            if pic.prepare_for_render(
+                frame_state,
+                data_stores,
+            ) {
+                if let Picture3DContext::In { root_data: None, plane_splitter_index, .. } = pic.context_3d {
+                    let dirty_rect = frame_state.current_dirty_region().combined;
+                    let splitter = &mut frame_state.plane_splitters[plane_splitter_index.0];
+                    let surface_index = pic.raster_config.as_ref().unwrap().surface_index;
+                    let surface = &frame_state.surfaces[surface_index.0];
+                    let local_prim_rect = surface.clipped_local_rect.cast_unit();
+
+                    PicturePrimitive::add_split_plane(
+                        splitter,
+                        frame_context.spatial_tree,
+                        prim_spatial_node_index,
+                        local_prim_rect,
+                        &prim_instance.vis.clip_chain.local_clip_rect,
+                        dirty_rect,
+                        plane_split_anchor,
+                    );
+                }
+
+                // If this picture uses segments, ensure the GPU cache is
+                // up to date with segment local rects.
+                // TODO(gw): This entire match statement above can now be
+                //           refactored into prepare_interned_prim_for_render.
+                if pic.can_use_segments() {
+                    write_segment(
+                        *segment_instance_index,
+                        frame_state,
+                        &mut scratch.segments,
+                        &mut scratch.segment_instances,
+                        |request| {
+                            request.push(PremultipliedColorF::WHITE);
+                            request.push(PremultipliedColorF::WHITE);
+                            request.push([
+                                -1.0,       // -ve means use prim rect for stretch size
+                                0.0,
+                                0.0,
+                                0.0,
+                            ]);
+                        }
+                    );
+                }
+            } else {
+                prim_instance.clear_visibility();
+            }
+        }
+        PrimitiveInstanceKind::BackdropCapture { .. } => {
+            // Register the owner picture of this backdrop primitive as the
+            // target for resolve of the sub-graph
+            frame_state.surface_builder.register_resolve_source();
+        }
+        PrimitiveInstanceKind::BackdropRender { pic_index, .. } => {
+            match frame_state.surface_builder.sub_graph_output_map.get(pic_index).cloned() {
+                Some(sub_graph_output_id) => {
+                    frame_state.surface_builder.add_child_render_task(
+                        sub_graph_output_id,
+                        frame_state.rg_builder,
+                    );
+                }
+                None => {
+                    // Backdrop capture was found not visible, didn't produce a sub-graph
+                    // so we can just skip drawing
+                    prim_instance.clear_visibility();
+                }
+            }
+        }
+    }
+
+    prim_cmd.unwrap_or(PrimitiveCommand::simple(prim_instance_index))
+}
+
+
+fn write_segment<F>(
+    segment_instance_index: SegmentInstanceIndex,
+    frame_state: &mut FrameBuildingState,
+    segments: &mut SegmentStorage,
+    segment_instances: &mut SegmentInstanceStorage,
+    f: F,
+) where F: Fn(&mut GpuDataRequest) {
+    debug_assert_ne!(segment_instance_index, SegmentInstanceIndex::INVALID);
+    if segment_instance_index != SegmentInstanceIndex::UNUSED {
+        let segment_instance = &mut segment_instances[segment_instance_index];
+
+        if let Some(mut request) = frame_state.gpu_cache.request(&mut segment_instance.gpu_cache_handle) {
+            let segments = &segments[segment_instance.segments_range];
+
+            f(&mut request);
+
+            for segment in segments {
+                request.write_segment(
+                    segment.local_rect,
+                    [0.0; 4],
+                );
+            }
+        }
+    }
+}
+
+fn decompose_repeated_gradient(
+    prim_vis: &PrimitiveVisibility,
+    prim_local_rect: &LayoutRect,
+    prim_spatial_node_index: SpatialNodeIndex,
+    stretch_size: &LayoutSize,
+    tile_spacing: &LayoutSize,
+    frame_state: &mut FrameBuildingState,
+    gradient_tiles: &mut GradientTileStorage,
+    spatial_tree: &SpatialTree,
+    mut callback: Option<&mut dyn FnMut(&LayoutRect, GpuDataRequest)>,
+) -> GradientTileRange {
+    let tile_range = gradient_tiles.open_range();
+
+    // Tighten the clip rect because decomposing the repeated image can
+    // produce primitives that are partially covering the original image
+    // rect and we want to clip these extra parts out.
+    if let Some(tight_clip_rect) = prim_vis
+        .clip_chain
+        .local_clip_rect
+        .intersection(prim_local_rect) {
+
+        let visible_rect = compute_conservative_visible_rect(
+            &prim_vis.clip_chain,
+            frame_state.current_dirty_region().combined,
+            prim_spatial_node_index,
+            spatial_tree,
+        );
+        let stride = *stretch_size + *tile_spacing;
+
+        let repetitions = image_tiling::repetitions(prim_local_rect, &visible_rect, stride);
+        gradient_tiles.reserve(repetitions.num_repetitions());
+        for Repetition { origin, .. } in repetitions {
+            let mut handle = GpuCacheHandle::new();
+            let rect = LayoutRect::from_origin_and_size(
+                origin,
+                *stretch_size,
+            );
+
+            if let Some(callback) = &mut callback {
+                if let Some(request) = frame_state.gpu_cache.request(&mut handle) {
+                    callback(&rect, request);
+                }
+            }
+
+            gradient_tiles.push(VisibleGradientTile {
+                local_rect: rect,
+                local_clip_rect: tight_clip_rect,
+                handle
+            });
+        }
+    }
+
+    // At this point if we don't have tiles to show it means we could probably
+    // have done a better a job at culling during an earlier stage.
+    gradient_tiles.close_range(tile_range)
+}
+
+
+fn update_clip_task_for_brush(
+    instance: &PrimitiveInstance,
+    prim_origin: &LayoutPoint,
+    prim_spatial_node_index: SpatialNodeIndex,
+    root_spatial_node_index: SpatialNodeIndex,
+    pic_context: &PictureContext,
+    pic_state: &mut PictureState,
+    frame_context: &FrameBuildingContext,
+    frame_state: &mut FrameBuildingState,
+    prim_store: &PrimitiveStore,
+    data_stores: &mut DataStores,
+    segments_store: &mut SegmentStorage,
+    segment_instances_store: &mut SegmentInstanceStorage,
+    clip_mask_instances: &mut Vec<ClipMaskKind>,
+    device_pixel_scale: DevicePixelScale,
+) -> Option<ClipTaskIndex> {
+    let segments = match instance.kind {
+        PrimitiveInstanceKind::TextRun { .. } |
+        PrimitiveInstanceKind::Clear { .. } |
+        PrimitiveInstanceKind::LineDecoration { .. } |
+        PrimitiveInstanceKind::BackdropCapture { .. } |
+        PrimitiveInstanceKind::BackdropRender { .. } => {
+            return None;
+        }
+        PrimitiveInstanceKind::Image { image_instance_index, .. } => {
+            let segment_instance_index = prim_store
+                .images[image_instance_index]
+                .segment_instance_index;
+
+            if segment_instance_index == SegmentInstanceIndex::UNUSED {
+                return None;
+            }
+
+            let segment_instance = &segment_instances_store[segment_instance_index];
+
+            &segments_store[segment_instance.segments_range]
+        }
+        PrimitiveInstanceKind::Picture { segment_instance_index, .. } => {
+            // Pictures may not support segment rendering at all (INVALID)
+            // or support segment rendering but choose not to due to size
+            // or some other factor (UNUSED).
+            if segment_instance_index == SegmentInstanceIndex::UNUSED ||
+               segment_instance_index == SegmentInstanceIndex::INVALID {
+                return None;
+            }
+
+            let segment_instance = &segment_instances_store[segment_instance_index];
+            &segments_store[segment_instance.segments_range]
+        }
+        PrimitiveInstanceKind::YuvImage { segment_instance_index, .. } |
+        PrimitiveInstanceKind::Rectangle { segment_instance_index, .. } => {
+            debug_assert!(segment_instance_index != SegmentInstanceIndex::INVALID);
+
+            if segment_instance_index == SegmentInstanceIndex::UNUSED {
+                return None;
+            }
+
+            let segment_instance = &segment_instances_store[segment_instance_index];
+
+            &segments_store[segment_instance.segments_range]
+        }
+        PrimitiveInstanceKind::ImageBorder { data_handle, .. } => {
+            let border_data = &data_stores.image_border[data_handle].kind;
+
+            // TODO: This is quite messy - once we remove legacy primitives we
+            //       can change this to be a tuple match on (instance, template)
+            border_data.brush_segments.as_slice()
+        }
+        PrimitiveInstanceKind::NormalBorder { data_handle, .. } => {
+            let border_data = &data_stores.normal_border[data_handle].kind;
+
+            // TODO: This is quite messy - once we remove legacy primitives we
+            //       can change this to be a tuple match on (instance, template)
+            border_data.brush_segments.as_slice()
+        }
+        PrimitiveInstanceKind::LinearGradient { data_handle, .. }
+        | PrimitiveInstanceKind::CachedLinearGradient { data_handle, .. } => {
+            let prim_data = &data_stores.linear_grad[data_handle];
+
+            // TODO: This is quite messy - once we remove legacy primitives we
+            //       can change this to be a tuple match on (instance, template)
+            if prim_data.brush_segments.is_empty() {
+                return None;
+            }
+
+            prim_data.brush_segments.as_slice()
+        }
+        PrimitiveInstanceKind::RadialGradient { data_handle, .. } => {
+            let prim_data = &data_stores.radial_grad[data_handle];
+
+            // TODO: This is quite messy - once we remove legacy primitives we
+            //       can change this to be a tuple match on (instance, template)
+            if prim_data.brush_segments.is_empty() {
+                return None;
+            }
+
+            prim_data.brush_segments.as_slice()
+        }
+        PrimitiveInstanceKind::ConicGradient { data_handle, .. } => {
+            let prim_data = &data_stores.conic_grad[data_handle];
+
+            // TODO: This is quite messy - once we remove legacy primitives we
+            //       can change this to be a tuple match on (instance, template)
+            if prim_data.brush_segments.is_empty() {
+                return None;
+            }
+
+            prim_data.brush_segments.as_slice()
+        }
+    };
+
+    // If there are no segments, early out to avoid setting a valid
+    // clip task instance location below.
+    if segments.is_empty() {
+        return None;
+    }
+
+    // Set where in the clip mask instances array the clip mask info
+    // can be found for this primitive. Each segment will push the
+    // clip mask information for itself in update_clip_task below.
+    let clip_task_index = ClipTaskIndex(clip_mask_instances.len() as _);
+
+    // If we only built 1 segment, there is no point in re-running
+    // the clip chain builder. Instead, just use the clip chain
+    // instance that was built for the main primitive. This is a
+    // significant optimization for the common case.
+    if segments.len() == 1 {
+        let clip_mask_kind = update_brush_segment_clip_task(
+            &segments[0],
+            Some(&instance.vis.clip_chain),
+            root_spatial_node_index,
+            pic_context.surface_index,
+            frame_context,
+            frame_state,
+            &mut data_stores.clip,
+            device_pixel_scale,
+        );
+        clip_mask_instances.push(clip_mask_kind);
+    } else {
+        let dirty_world_rect = frame_state.current_dirty_region().combined;
+
+        for segment in segments {
+            // Build a clip chain for the smaller segment rect. This will
+            // often manage to eliminate most/all clips, and sometimes
+            // clip the segment completely.
+            frame_state.clip_store.set_active_clips_from_clip_chain(
+                &instance.vis.clip_chain,
+                prim_spatial_node_index,
+                &frame_context.spatial_tree,
+                &data_stores.clip,
+            );
+
+            let segment_clip_chain = frame_state
+                .clip_store
+                .build_clip_chain_instance(
+                    segment.local_rect.translate(prim_origin.to_vector()),
+                    &pic_state.map_local_to_pic,
+                    &pic_state.map_pic_to_world,
+                    &frame_context.spatial_tree,
+                    frame_state.gpu_cache,
+                    frame_state.resource_cache,
+                    device_pixel_scale,
+                    &dirty_world_rect,
+                    &mut data_stores.clip,
+                    false,
+                );
+
+            let clip_mask_kind = update_brush_segment_clip_task(
+                &segment,
+                segment_clip_chain.as_ref(),
+                root_spatial_node_index,
+                pic_context.surface_index,
+                frame_context,
+                frame_state,
+                &mut data_stores.clip,
+                device_pixel_scale,
+            );
+            clip_mask_instances.push(clip_mask_kind);
+        }
+    }
+
+    Some(clip_task_index)
+}
+
+pub fn update_clip_task(
+    instance: &mut PrimitiveInstance,
+    prim_origin: &LayoutPoint,
+    prim_spatial_node_index: SpatialNodeIndex,
+    root_spatial_node_index: SpatialNodeIndex,
+    pic_context: &PictureContext,
+    pic_state: &mut PictureState,
+    frame_context: &FrameBuildingContext,
+    frame_state: &mut FrameBuildingState,
+    prim_store: &mut PrimitiveStore,
+    data_stores: &mut DataStores,
+    scratch: &mut PrimitiveScratchBuffer,
+) -> bool {
+    let device_pixel_scale = frame_state.surfaces[pic_context.surface_index.0].device_pixel_scale;
+
+    build_segments_if_needed(
+        instance,
+        frame_state,
+        prim_store,
+        data_stores,
+        &mut scratch.segments,
+        &mut scratch.segment_instances,
+    );
+
+    // First try to  render this primitive's mask using optimized brush rendering.
+    instance.vis.clip_task_index = if let Some(clip_task_index) = update_clip_task_for_brush(
+        instance,
+        prim_origin,
+        prim_spatial_node_index,
+        root_spatial_node_index,
+        pic_context,
+        pic_state,
+        frame_context,
+        frame_state,
+        prim_store,
+        data_stores,
+        &mut scratch.segments,
+        &mut scratch.segment_instances,
+        &mut scratch.clip_mask_instances,
+        device_pixel_scale,
+    ) {
+        clip_task_index
+    } else if instance.vis.clip_chain.needs_mask {
+        // Get a minimal device space rect, clipped to the screen that we
+        // need to allocate for the clip mask, as well as interpolated
+        // snap offsets.
+        let unadjusted_device_rect = match frame_state.surfaces[pic_context.surface_index.0].get_surface_rect(
+            &instance.vis.clip_chain.pic_coverage_rect,
+            frame_context.spatial_tree,
+        ) {
+            Some(rect) => rect,
+            None => return false,
+        };
+
+        let (device_rect, device_pixel_scale) = adjust_mask_scale_for_max_size(
+            unadjusted_device_rect,
+            device_pixel_scale,
+        );
+        let clip_task_id = RenderTaskKind::new_mask(
+            device_rect,
+            instance.vis.clip_chain.clips_range,
+            root_spatial_node_index,
+            frame_state.clip_store,
+            frame_state.gpu_cache,
+            frame_state.frame_gpu_data,
+            frame_state.resource_cache,
+            frame_state.rg_builder,
+            &mut data_stores.clip,
+            device_pixel_scale,
+            frame_context.fb_config,
+            &mut frame_state.surface_builder,
+        );
+        // Set the global clip mask instance for this primitive.
+        let clip_task_index = ClipTaskIndex(scratch.clip_mask_instances.len() as _);
+        scratch.clip_mask_instances.push(ClipMaskKind::Mask(clip_task_id));
+        instance.vis.clip_task_index = clip_task_index;
+        frame_state.surface_builder.add_child_render_task(
+            clip_task_id,
+            frame_state.rg_builder,
+        );
+        clip_task_index
+    } else {
+        ClipTaskIndex::INVALID
+    };
+
+    true
+}
+
+/// Write out to the clip mask instances array the correct clip mask
+/// config for this segment.
+pub fn update_brush_segment_clip_task(
+    segment: &BrushSegment,
+    clip_chain: Option<&ClipChainInstance>,
+    root_spatial_node_index: SpatialNodeIndex,
+    surface_index: SurfaceIndex,
+    frame_context: &FrameBuildingContext,
+    frame_state: &mut FrameBuildingState,
+    clip_data_store: &mut ClipDataStore,
+    device_pixel_scale: DevicePixelScale,
+) -> ClipMaskKind {
+    let clip_chain = match clip_chain {
+        Some(chain) => chain,
+        None => return ClipMaskKind::Clipped,
+    };
+    if !clip_chain.needs_mask ||
+       (!segment.may_need_clip_mask && !clip_chain.has_non_local_clips) {
+        return ClipMaskKind::None;
+    }
+
+    let device_rect = match frame_state.surfaces[surface_index.0].get_surface_rect(
+        &clip_chain.pic_coverage_rect,
+        frame_context.spatial_tree,
+    ) {
+        Some(rect) => rect,
+        None => return ClipMaskKind::Clipped,
+    };
+
+    let (device_rect, device_pixel_scale) = adjust_mask_scale_for_max_size(device_rect, device_pixel_scale);
+
+    let clip_task_id = RenderTaskKind::new_mask(
+        device_rect,
+        clip_chain.clips_range,
+        root_spatial_node_index,
+        frame_state.clip_store,
+        frame_state.gpu_cache,
+        frame_state.frame_gpu_data,
+        frame_state.resource_cache,
+        frame_state.rg_builder,
+        clip_data_store,
+        device_pixel_scale,
+        frame_context.fb_config,
+        &mut frame_state.surface_builder,
+    );
+
+    frame_state.surface_builder.add_child_render_task(
+        clip_task_id,
+        frame_state.rg_builder,
+    );
+    ClipMaskKind::Mask(clip_task_id)
+}
+
+
+fn write_brush_segment_description(
+    prim_local_rect: LayoutRect,
+    prim_local_clip_rect: LayoutRect,
+    clip_chain: &ClipChainInstance,
+    segment_builder: &mut SegmentBuilder,
+    clip_store: &ClipStore,
+    data_stores: &DataStores,
+) -> bool {
+    // If the brush is small, we want to skip building segments
+    // and just draw it as a single primitive with clip mask.
+    if prim_local_rect.area() < MIN_BRUSH_SPLIT_AREA {
+        return false;
+    }
+
+    // NOTE: The local clip rect passed to the segment builder must be the unmodified
+    //       local clip rect from the clip leaf, not the local_clip_rect from the
+    //       clip-chain instance. The clip-chain instance may have been reduced by
+    //       clips that are in the same coordinate system, but not the same spatial
+    //       node as the primitive. This can result in the clip for the segment building
+    //       being affected by scrolling clips, which we can't handle (since the segments
+    //       are not invalidated during frame building after being built).
+    segment_builder.initialize(
+        prim_local_rect,
+        None,
+        prim_local_clip_rect,
+    );
+
+    // Segment the primitive on all the local-space clip sources that we can.
+    for i in 0 .. clip_chain.clips_range.count {
+        let clip_instance = clip_store
+            .get_instance_from_range(&clip_chain.clips_range, i);
+        let clip_node = &data_stores.clip[clip_instance.handle];
+
+        // If this clip item is positioned by another positioning node, its relative position
+        // could change during scrolling. This means that we would need to resegment. Instead
+        // of doing that, only segment with clips that have the same positioning node.
+        // TODO(mrobinson, #2858): It may make sense to include these nodes, resegmenting only
+        // when necessary while scrolling.
+        if !clip_instance.flags.contains(ClipNodeFlags::SAME_SPATIAL_NODE) {
+            continue;
+        }
+
+        let (local_clip_rect, radius, mode) = match clip_node.item.kind {
+            ClipItemKind::RoundedRectangle { rect, radius, mode } => {
+                (rect, Some(radius), mode)
+            }
+            ClipItemKind::Rectangle { rect, mode } => {
+                (rect, None, mode)
+            }
+            ClipItemKind::BoxShadow { ref source } => {
+                // For inset box shadows, we can clip out any
+                // pixels that are inside the shadow region
+                // and are beyond the inner rect, as they can't
+                // be affected by the blur radius.
+                let inner_clip_mode = match source.clip_mode {
+                    BoxShadowClipMode::Outset => None,
+                    BoxShadowClipMode::Inset => Some(ClipMode::ClipOut),
+                };
+
+                // Push a region into the segment builder where the
+                // box-shadow can have an effect on the result. This
+                // ensures clip-mask tasks get allocated for these
+                // pixel regions, even if no other clips affect them.
+                segment_builder.push_mask_region(
+                    source.prim_shadow_rect,
+                    source.prim_shadow_rect.inflate(
+                        -0.5 * source.original_alloc_size.width,
+                        -0.5 * source.original_alloc_size.height,
+                    ),
+                    inner_clip_mode,
+                );
+
+                continue;
+            }
+            ClipItemKind::Image { .. } => {
+                // If we encounter an image mask, bail out from segment building.
+                // It's not possible to know which parts of the primitive are affected
+                // by the mask (without inspecting the pixels). We could do something
+                // better here in the future if it ever shows up as a performance issue
+                // (for instance, at least segment based on the bounding rect of the
+                // image mask if it's non-repeating).
+                return false;
+            }
+        };
+
+        segment_builder.push_clip_rect(local_clip_rect, radius, mode);
+    }
+
+    true
+}
+
+fn build_segments_if_needed(
+    instance: &mut PrimitiveInstance,
+    frame_state: &mut FrameBuildingState,
+    prim_store: &mut PrimitiveStore,
+    data_stores: &DataStores,
+    segments_store: &mut SegmentStorage,
+    segment_instances_store: &mut SegmentInstanceStorage,
+) {
+    let prim_clip_chain = &instance.vis.clip_chain;
+
+    // Usually, the primitive rect can be found from information
+    // in the instance and primitive template.
+    let prim_local_rect = data_stores.get_local_prim_rect(
+        instance,
+        &prim_store.pictures,
+        frame_state.surfaces,
+    );
+
+    let segment_instance_index = match instance.kind {
+        PrimitiveInstanceKind::Rectangle { ref mut segment_instance_index, .. } |
+        PrimitiveInstanceKind::YuvImage { ref mut segment_instance_index, .. } => {
+            segment_instance_index
+        }
+        PrimitiveInstanceKind::Image { data_handle, image_instance_index, .. } => {
+            let image_data = &data_stores.image[data_handle].kind;
+            let image_instance = &mut prim_store.images[image_instance_index];
+            //Note: tiled images don't support automatic segmentation,
+            // they strictly produce one segment per visible tile instead.
+            if frame_state
+                .resource_cache
+                .get_image_properties(image_data.key)
+                .and_then(|properties| properties.tiling)
+                .is_some()
+            {
+                image_instance.segment_instance_index = SegmentInstanceIndex::UNUSED;
+                return;
+            }
+            &mut image_instance.segment_instance_index
+        }
+        PrimitiveInstanceKind::Picture { ref mut segment_instance_index, pic_index, .. } => {
+            let pic = &mut prim_store.pictures[pic_index.0];
+
+            // If this picture supports segment rendering
+            if pic.can_use_segments() {
+                // If the segments have been invalidated, ensure the current
+                // index of segments is invalid. This ensures that the segment
+                // building logic below will be run.
+                if !pic.segments_are_valid {
+                    *segment_instance_index = SegmentInstanceIndex::INVALID;
+                    pic.segments_are_valid = true;
+                }
+
+                segment_instance_index
+            } else {
+                return;
+            }
+        }
+        PrimitiveInstanceKind::TextRun { .. } |
+        PrimitiveInstanceKind::NormalBorder { .. } |
+        PrimitiveInstanceKind::ImageBorder { .. } |
+        PrimitiveInstanceKind::Clear { .. } |
+        PrimitiveInstanceKind::LinearGradient { .. } |
+        PrimitiveInstanceKind::CachedLinearGradient { .. } |
+        PrimitiveInstanceKind::RadialGradient { .. } |
+        PrimitiveInstanceKind::ConicGradient { .. } |
+        PrimitiveInstanceKind::LineDecoration { .. } |
+        PrimitiveInstanceKind::BackdropCapture { .. } |
+        PrimitiveInstanceKind::BackdropRender { .. } => {
+            // These primitives don't support / need segments.
+            return;
+        }
+    };
+
+    if *segment_instance_index == SegmentInstanceIndex::INVALID {
+        let mut segments: SmallVec<[BrushSegment; 8]> = SmallVec::new();
+        let clip_leaf = frame_state.clip_tree.get_leaf(instance.clip_leaf_id);
+
+        if write_brush_segment_description(
+            prim_local_rect,
+            clip_leaf.local_clip_rect,
+            prim_clip_chain,
+            &mut frame_state.segment_builder,
+            frame_state.clip_store,
+            data_stores,
+        ) {
+            frame_state.segment_builder.build(|segment| {
+                segments.push(
+                    BrushSegment::new(
+                        segment.rect.translate(-prim_local_rect.min.to_vector()),
+                        segment.has_mask,
+                        segment.edge_flags,
+                        [0.0; 4],
+                        BrushFlags::PERSPECTIVE_INTERPOLATION,
+                    ),
+                );
+            });
+        }
+
+        // If only a single segment is produced, there is no benefit to writing
+        // a segment instance array. Instead, just use the main primitive rect
+        // written into the GPU cache.
+        // TODO(gw): This is (sortof) a bandaid - due to a limitation in the current
+        //           brush encoding, we can only support a total of up to 2^16 segments.
+        //           This should be (more than) enough for any real world case, so for
+        //           now we can handle this by skipping cases where we were generating
+        //           segments where there is no benefit. The long term / robust fix
+        //           for this is to move the segment building to be done as a more
+        //           limited nine-patch system during scene building, removing arbitrary
+        //           segmentation during frame-building (see bug #1617491).
+        if segments.len() <= 1 {
+            *segment_instance_index = SegmentInstanceIndex::UNUSED;
+        } else {
+            let segments_range = segments_store.extend(segments);
+
+            let instance = SegmentedInstance {
+                segments_range,
+                gpu_cache_handle: GpuCacheHandle::new(),
+            };
+
+            *segment_instance_index = segment_instances_store.push(instance);
+        };
+    }
+}
+
+// Ensures that the size of mask render tasks are within MAX_MASK_SIZE.
+fn adjust_mask_scale_for_max_size(device_rect: DeviceRect, device_pixel_scale: DevicePixelScale) -> (DeviceRect, DevicePixelScale) {
+    if device_rect.width() > MAX_MASK_SIZE || device_rect.height() > MAX_MASK_SIZE {
+        // round_out will grow by 1 integer pixel if origin is on a
+        // fractional position, so keep that margin for error with -1:
+        let scale = (MAX_MASK_SIZE - 1.0) /
+            f32::max(device_rect.width(), device_rect.height());
+        let new_device_pixel_scale = device_pixel_scale * Scale::new(scale);
+        let new_device_rect = (device_rect.to_f32() * Scale::new(scale))
+            .round_out();
+        (new_device_rect, new_device_pixel_scale)
+    } else {
+        (device_rect, device_pixel_scale)
+    }
+}
+