Adding upstream version 115.7.0esr.upstream/115.7.0esr

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

1 files changed, 745 insertions, 0 deletions

diff --git a/gfx/wr/webrender/src/tile_cache.rs b/gfx/wr/webrender/src/tile_cache.rs
new file mode 100644
index 0000000000..3b2600d0c0
--- /dev/null
+++ b/gfx/wr/webrender/src/tile_cache.rs
@@ -0,0 +1,745 @@
+/* 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 api::{ColorF, PrimitiveFlags, QualitySettings, RasterSpace, ClipId};
+use api::units::*;
+use crate::clip::{ClipNodeKind, ClipLeafId, ClipNodeId, ClipTreeBuilder};
+use crate::frame_builder::FrameBuilderConfig;
+use crate::internal_types::{FastHashMap};
+use crate::picture::{PrimitiveList, PictureCompositeMode, PicturePrimitive, SliceId};
+use crate::picture::{Picture3DContext, TileCacheParams, TileOffset, PictureFlags};
+use crate::prim_store::{PrimitiveInstance, PrimitiveStore, PictureIndex};
+use crate::scene_building::SliceFlags;
+use crate::scene_builder_thread::Interners;
+use crate::spatial_tree::{SpatialNodeIndex, SceneSpatialTree};
+use crate::util::VecHelper;
+use std::mem;
+
+/*
+ Types and functionality related to picture caching. In future, we'll
+ move more and more of the existing functionality out of picture.rs
+ and into here.
+ */
+
+// If the page would create too many slices (an arbitrary definition where
+// it's assumed the GPU memory + compositing overhead would be too high)
+// then create a single picture cache for the remaining content. This at
+// least means that we can cache small content changes efficiently when
+// scrolling isn't occurring. Scrolling regions will be handled reasonably
+// efficiently by the dirty rect tracking (since it's likely that if the
+// page has so many slices there isn't a single major scroll region).
+const MAX_CACHE_SLICES: usize = 12;
+
+struct SliceDescriptor {
+    prim_list: PrimitiveList,
+    scroll_root: SpatialNodeIndex,
+    shared_clip_node_id: ClipNodeId,
+}
+
+enum SliceKind {
+    Default {
+        secondary_slices: Vec<SliceDescriptor>,
+    },
+    Atomic {
+        prim_list: PrimitiveList,
+    },
+}
+
+impl SliceKind {
+    fn default() -> Self {
+        SliceKind::Default {
+            secondary_slices: Vec::new(),
+        }
+    }
+}
+
+struct PrimarySlice {
+    /// Whether this slice is atomic or has secondary slice(s)
+    kind: SliceKind,
+    /// Optional background color of this slice
+    background_color: Option<ColorF>,
+    /// Optional root clip for the iframe
+    iframe_clip: Option<ClipId>,
+    /// Information about how to draw and composite this slice
+    slice_flags: SliceFlags,
+}
+
+impl PrimarySlice {
+    fn new(
+        slice_flags: SliceFlags,
+        iframe_clip: Option<ClipId>,
+        background_color: Option<ColorF>,
+    ) -> Self {
+        PrimarySlice {
+            kind: SliceKind::default(),
+            background_color,
+            iframe_clip,
+            slice_flags,
+        }
+    }
+
+    fn has_too_many_slices(&self) -> bool {
+        match self.kind {
+            SliceKind::Atomic { .. } => false,
+            SliceKind::Default { ref secondary_slices } => secondary_slices.len() > MAX_CACHE_SLICES,
+        }
+    }
+
+    fn merge(&mut self) {
+        self.slice_flags |= SliceFlags::IS_ATOMIC;
+
+        let old = mem::replace(
+            &mut self.kind,
+            SliceKind::Default { secondary_slices: Vec::new() },
+        );
+
+        self.kind = match old {
+            SliceKind::Default { mut secondary_slices } => {
+                let mut prim_list = PrimitiveList::empty();
+
+                for descriptor in secondary_slices.drain(..) {
+                    prim_list.merge(descriptor.prim_list);
+                }
+
+                SliceKind::Atomic {
+                    prim_list,
+                }
+            }
+            atomic => atomic,
+        }
+    }
+}
+
+/// Used during scene building to construct the list of pending tile caches.
+pub struct TileCacheBuilder {
+    /// List of tile caches that have been created so far (last in the list is currently active).
+    primary_slices: Vec<PrimarySlice>,
+    /// Cache the previous scroll root search for a spatial node, since they are often the same.
+    prev_scroll_root_cache: (SpatialNodeIndex, SpatialNodeIndex),
+    /// Handle to the root reference frame
+    root_spatial_node_index: SpatialNodeIndex,
+}
+
+/// The output of a tile cache builder, containing all details needed to construct the
+/// tile cache(s) for the next scene, and retain tiles from the previous frame when sent
+/// send to the frame builder.
+pub struct TileCacheConfig {
+    /// Mapping of slice id to the parameters needed to construct this tile cache.
+    pub tile_caches: FastHashMap<SliceId, TileCacheParams>,
+    /// Number of picture cache slices that were created (for profiler)
+    pub picture_cache_slice_count: usize,
+}
+
+impl TileCacheConfig {
+    pub fn new(picture_cache_slice_count: usize) -> Self {
+        TileCacheConfig {
+            tile_caches: FastHashMap::default(),
+            picture_cache_slice_count,
+        }
+    }
+}
+
+impl TileCacheBuilder {
+    /// Construct a new tile cache builder.
+    pub fn new(
+        root_spatial_node_index: SpatialNodeIndex,
+        background_color: Option<ColorF>,
+    ) -> Self {
+        TileCacheBuilder {
+            primary_slices: vec![PrimarySlice::new(SliceFlags::empty(), None, background_color)],
+            prev_scroll_root_cache: (SpatialNodeIndex::INVALID, SpatialNodeIndex::INVALID),
+            root_spatial_node_index,
+        }
+    }
+
+    pub fn make_current_slice_atomic(&mut self) {
+        self.primary_slices
+            .last_mut()
+            .unwrap()
+            .merge();
+    }
+
+    /// Returns true if the current slice has no primitives added yet
+    pub fn is_current_slice_empty(&self) -> bool {
+        match self.primary_slices.last() {
+            Some(slice) => {
+                match slice.kind {
+                    SliceKind::Default { ref secondary_slices } => {
+                        secondary_slices.is_empty()
+                    }
+                    SliceKind::Atomic { ref prim_list } => {
+                        prim_list.is_empty()
+                    }
+                }
+            }
+            None => {
+                true
+            }
+        }
+    }
+
+    /// Set a barrier that forces a new tile cache next time a prim is added.
+    pub fn add_tile_cache_barrier(
+        &mut self,
+        slice_flags: SliceFlags,
+        iframe_clip: Option<ClipId>,
+    ) {
+        let new_slice = PrimarySlice::new(
+            slice_flags,
+            iframe_clip,
+            None,
+        );
+
+        self.primary_slices.push(new_slice);
+    }
+
+    /// Create a new tile cache for an existing prim_list
+    fn build_tile_cache(
+        &mut self,
+        prim_list: PrimitiveList,
+        spatial_tree: &SceneSpatialTree,
+        prim_instances: &[PrimitiveInstance],
+        clip_tree_builder: &ClipTreeBuilder,
+    ) -> Option<SliceDescriptor> {
+        if prim_list.is_empty() {
+            return None;
+        }
+
+        // Iterate the clusters and determine which is the most commonly occurring
+        // scroll root. This is a reasonable heuristic to decide which spatial node
+        // should be considered the scroll root of this tile cache, in order to
+        // minimize the invalidations that occur due to scrolling. It's often the
+        // case that a blend container will have only a single scroll root.
+        let mut scroll_root_occurrences = FastHashMap::default();
+
+        for cluster in &prim_list.clusters {
+            // If we encounter a cluster which has an unknown spatial node,
+            // we don't include that in the set of spatial nodes that we
+            // are trying to find scroll roots for. Later on, in finalize_picture,
+            // the cluster spatial node will be updated to the selected scroll root.
+            if cluster.spatial_node_index == SpatialNodeIndex::UNKNOWN {
+                continue;
+            }
+
+            let scroll_root = find_scroll_root(
+                cluster.spatial_node_index,
+                &mut self.prev_scroll_root_cache,
+                spatial_tree,
+            );
+
+            *scroll_root_occurrences.entry(scroll_root).or_insert(0) += 1;
+        }
+
+        // We can't just select the most commonly occurring scroll root in this
+        // primitive list. If that is a nested scroll root, there may be
+        // primitives in the list that are outside that scroll root, which
+        // can cause panics when calculating relative transforms. To ensure
+        // this doesn't happen, only retain scroll root candidates that are
+        // also ancestors of every other scroll root candidate.
+        let scroll_roots: Vec<SpatialNodeIndex> = scroll_root_occurrences
+            .keys()
+            .cloned()
+            .collect();
+
+        scroll_root_occurrences.retain(|parent_spatial_node_index, _| {
+            scroll_roots.iter().all(|child_spatial_node_index| {
+                parent_spatial_node_index == child_spatial_node_index ||
+                spatial_tree.is_ancestor(
+                    *parent_spatial_node_index,
+                    *child_spatial_node_index,
+                )
+            })
+        });
+
+        // Select the scroll root by finding the most commonly occurring one
+        let scroll_root = scroll_root_occurrences
+            .iter()
+            .max_by_key(|entry | entry.1)
+            .map(|(spatial_node_index, _)| *spatial_node_index)
+            .unwrap_or(self.root_spatial_node_index);
+
+        // Work out which clips are shared by all prim instances and can thus be applied
+        // at the tile cache level. In future, we aim to remove this limitation by knowing
+        // during initial scene build which are the relevant compositor clips, but for now
+        // this is unlikely to be a significant cost.
+        let mut shared_clip_node_id = None;
+
+        for cluster in &prim_list.clusters {
+            for prim_instance in &prim_instances[cluster.prim_range()] {
+                let leaf = clip_tree_builder.get_leaf(prim_instance.clip_leaf_id);
+
+                // TODO(gw): Need to cache last clip-node id here?
+                shared_clip_node_id = match shared_clip_node_id {
+                    Some(current) => {
+                        Some(clip_tree_builder.find_lowest_common_ancestor(current, leaf.node_id))
+                    }
+                    None => {
+                        Some(leaf.node_id)
+                    }
+                }
+            }
+        }
+
+        let shared_clip_node_id = shared_clip_node_id.expect("bug: no shared clip root");
+
+        Some(SliceDescriptor {
+            scroll_root,
+            shared_clip_node_id,
+            prim_list,
+        })
+    }
+
+    /// Add a primitive, either to the current tile cache, or a new one, depending on various conditions.
+    pub fn add_prim(
+        &mut self,
+        prim_instance: PrimitiveInstance,
+        prim_rect: LayoutRect,
+        spatial_node_index: SpatialNodeIndex,
+        prim_flags: PrimitiveFlags,
+        spatial_tree: &SceneSpatialTree,
+        interners: &Interners,
+        quality_settings: &QualitySettings,
+        prim_instances: &mut Vec<PrimitiveInstance>,
+        clip_tree_builder: &ClipTreeBuilder,
+    ) {
+        let primary_slice = self.primary_slices.last_mut().unwrap();
+
+        match primary_slice.kind {
+            SliceKind::Atomic { ref mut prim_list } => {
+                prim_list.add_prim(
+                    prim_instance,
+                    prim_rect,
+                    spatial_node_index,
+                    prim_flags,
+                    prim_instances,
+                    clip_tree_builder,
+                );
+            }
+            SliceKind::Default { ref mut secondary_slices } => {
+                assert_ne!(spatial_node_index, SpatialNodeIndex::UNKNOWN);
+
+                // Check if we want to create a new slice based on the current / next scroll root
+                let scroll_root = find_scroll_root(
+                    spatial_node_index,
+                    &mut self.prev_scroll_root_cache,
+                    spatial_tree,
+                );
+
+                let current_scroll_root = secondary_slices
+                    .last()
+                    .map(|p| p.scroll_root);
+
+                let mut want_new_tile_cache = secondary_slices.is_empty();
+
+                if let Some(current_scroll_root) = current_scroll_root {
+                    want_new_tile_cache |= match (current_scroll_root, scroll_root) {
+                        (_, _) if current_scroll_root == self.root_spatial_node_index && scroll_root == self.root_spatial_node_index => {
+                            // Both current slice and this cluster are fixed position, no need to cut
+                            false
+                        }
+                        (_, _) if current_scroll_root == self.root_spatial_node_index => {
+                            // A real scroll root is being established, so create a cache slice
+                            true
+                        }
+                        (_, _) if scroll_root == self.root_spatial_node_index => {
+                            // If quality settings force subpixel AA over performance, skip creating
+                            // a slice for the fixed position element(s) here.
+                            if quality_settings.force_subpixel_aa_where_possible {
+                                false
+                            } else {
+                                // A fixed position slice is encountered within a scroll root. Only create
+                                // a slice in this case if all the clips referenced by this cluster are also
+                                // fixed position. There's no real point in creating slices for these cases,
+                                // since we'll have to rasterize them as the scrolling clip moves anyway. It
+                                // also allows us to retain subpixel AA in these cases. For these types of
+                                // slices, the intra-slice dirty rect handling typically works quite well
+                                // (a common case is parallax scrolling effects).
+                                let mut create_slice = true;
+
+                                let leaf = clip_tree_builder.get_leaf(prim_instance.clip_leaf_id);
+                                let mut current_node_id = leaf.node_id;
+
+                                while current_node_id != ClipNodeId::NONE {
+                                    let node = clip_tree_builder.get_node(current_node_id);
+
+                                    let clip_node_data = &interners.clip[node.handle];
+
+                                    let spatial_root = find_scroll_root(
+                                        clip_node_data.key.spatial_node_index,
+                                        &mut self.prev_scroll_root_cache,
+                                        spatial_tree,
+                                    );
+
+                                    if spatial_root != self.root_spatial_node_index {
+                                        create_slice = false;
+                                        break;
+                                    }
+
+                                    current_node_id = node.parent;
+                                }
+
+                                create_slice
+                            }
+                        }
+                        (curr_scroll_root, scroll_root) => {
+                            // Two scrolling roots - only need a new slice if they differ
+                            curr_scroll_root != scroll_root
+                        }
+                    };
+
+                    // Update the list of clips that apply to this primitive instance, to track which are the
+                    // shared clips for this tile cache that can be applied during compositing.
+
+                    let shared_clip_node_id = find_shared_clip_root(
+                        current_scroll_root,
+                        prim_instance.clip_leaf_id,
+                        spatial_tree,
+                        clip_tree_builder,
+                        interners,
+                    );
+
+                    let current_shared_clip_node_id = secondary_slices.last().unwrap().shared_clip_node_id;
+
+                    // If the shared clips are not compatible, create a new slice.
+                    want_new_tile_cache |= shared_clip_node_id != current_shared_clip_node_id;
+                }
+
+                if want_new_tile_cache {
+
+                    let shared_clip_node_id = find_shared_clip_root(
+                        scroll_root,
+                        prim_instance.clip_leaf_id,
+                        spatial_tree,
+                        clip_tree_builder,
+                        interners,
+                    );
+
+                    secondary_slices.push(SliceDescriptor {
+                        prim_list: PrimitiveList::empty(),
+                        scroll_root,
+                        shared_clip_node_id,
+                    });
+                }
+
+                secondary_slices
+                    .last_mut()
+                    .unwrap()
+                    .prim_list
+                    .add_prim(
+                        prim_instance,
+                        prim_rect,
+                        spatial_node_index,
+                        prim_flags,
+                        prim_instances,
+                        clip_tree_builder,
+                    );
+            }
+        }
+    }
+
+    /// Consume this object and build the list of tile cache primitives
+    pub fn build(
+        mut self,
+        config: &FrameBuilderConfig,
+        prim_store: &mut PrimitiveStore,
+        spatial_tree: &SceneSpatialTree,
+        prim_instances: &[PrimitiveInstance],
+        clip_tree_builder: &mut ClipTreeBuilder,
+    ) -> (TileCacheConfig, Vec<PictureIndex>) {
+        let mut result = TileCacheConfig::new(self.primary_slices.len());
+        let mut tile_cache_pictures = Vec::new();
+        let primary_slices = std::mem::replace(&mut self.primary_slices, Vec::new());
+
+        for mut primary_slice in primary_slices {
+
+            if primary_slice.has_too_many_slices() {
+                primary_slice.merge();
+            }
+
+            match primary_slice.kind {
+                SliceKind::Atomic { prim_list } => {
+                    if let Some(descriptor) = self.build_tile_cache(
+                        prim_list,
+                        spatial_tree,
+                        prim_instances,
+                        clip_tree_builder,
+                    ) {
+                        create_tile_cache(
+                            primary_slice.slice_flags,
+                            descriptor.scroll_root,
+                            primary_slice.iframe_clip,
+                            descriptor.prim_list,
+                            primary_slice.background_color,
+                            descriptor.shared_clip_node_id,
+                            prim_store,
+                            config,
+                            &mut result.tile_caches,
+                            &mut tile_cache_pictures,
+                            clip_tree_builder,
+                        );
+                    }
+                }
+                SliceKind::Default { secondary_slices } => {
+                    for descriptor in secondary_slices {
+                        create_tile_cache(
+                            primary_slice.slice_flags,
+                            descriptor.scroll_root,
+                            primary_slice.iframe_clip,
+                            descriptor.prim_list,
+                            primary_slice.background_color,
+                            descriptor.shared_clip_node_id,
+                            prim_store,
+                            config,
+                            &mut result.tile_caches,
+                            &mut tile_cache_pictures,
+                            clip_tree_builder,
+                        );
+                    }
+                }
+            }
+        }
+
+        (result, tile_cache_pictures)
+    }
+}
+
+/// Find the scroll root for a given spatial node
+fn find_scroll_root(
+    spatial_node_index: SpatialNodeIndex,
+    prev_scroll_root_cache: &mut (SpatialNodeIndex, SpatialNodeIndex),
+    spatial_tree: &SceneSpatialTree,
+) -> SpatialNodeIndex {
+    if prev_scroll_root_cache.0 == spatial_node_index {
+        return prev_scroll_root_cache.1;
+    }
+
+    let scroll_root = spatial_tree.find_scroll_root(spatial_node_index);
+    *prev_scroll_root_cache = (spatial_node_index, scroll_root);
+
+    scroll_root
+}
+
+fn find_shared_clip_root(
+    scroll_root: SpatialNodeIndex,
+    clip_leaf_id: ClipLeafId,
+    spatial_tree: &SceneSpatialTree,
+    clip_tree_builder: &ClipTreeBuilder,
+    interners: &Interners,
+) -> ClipNodeId {
+    let leaf = clip_tree_builder.get_leaf(clip_leaf_id);
+    let mut current_node_id = leaf.node_id;
+
+    while current_node_id != ClipNodeId::NONE {
+        let node = clip_tree_builder.get_node(current_node_id);
+
+        let clip_node_data = &interners.clip[node.handle];
+
+        if let ClipNodeKind::Rectangle = clip_node_data.key.kind.node_kind() {
+            let is_ancestor = spatial_tree.is_ancestor(
+                clip_node_data.key.spatial_node_index,
+                scroll_root,
+            );
+
+            let has_complex_clips = clip_tree_builder.clip_node_has_complex_clips(
+                current_node_id,
+                interners,
+            );
+
+            if is_ancestor && !has_complex_clips {
+                break;
+            }
+        }
+
+        current_node_id = node.parent;
+    }
+
+    current_node_id
+}
+
+/// Given a PrimitiveList and scroll root, construct a tile cache primitive instance
+/// that wraps the primitive list.
+fn create_tile_cache(
+    slice_flags: SliceFlags,
+    scroll_root: SpatialNodeIndex,
+    iframe_clip: Option<ClipId>,
+    prim_list: PrimitiveList,
+    background_color: Option<ColorF>,
+    shared_clip_node_id: ClipNodeId,
+    prim_store: &mut PrimitiveStore,
+    frame_builder_config: &FrameBuilderConfig,
+    tile_caches: &mut FastHashMap<SliceId, TileCacheParams>,
+    tile_cache_pictures: &mut Vec<PictureIndex>,
+    clip_tree_builder: &mut ClipTreeBuilder,
+) {
+    // Accumulate any clip instances from the iframe_clip into the shared clips
+    // that will be applied by this tile cache during compositing.
+    let mut additional_clips = Vec::new();
+
+    if let Some(clip_id) = iframe_clip {
+        additional_clips.push(clip_id);
+    }
+
+    let shared_clip_leaf_id = Some(clip_tree_builder.build_for_tile_cache(
+        shared_clip_node_id,
+        &additional_clips,
+    ));
+
+    // Build a clip-chain for the tile cache, that contains any of the shared clips
+    // we will apply when drawing the tiles. In all cases provided by Gecko, these
+    // are rectangle clips with a scale/offset transform only, and get handled as
+    // a simple local clip rect in the vertex shader. However, this should in theory
+    // also work with any complex clips, such as rounded rects and image masks, by
+    // producing a clip mask that is applied to the picture cache tiles.
+
+    let slice = tile_cache_pictures.len();
+
+    let background_color = if slice == 0 {
+        background_color
+    } else {
+        None
+    };
+
+    let slice_id = SliceId::new(slice);
+
+    // Store some information about the picture cache slice. This is used when we swap the
+    // new scene into the frame builder to either reuse existing slices, or create new ones.
+    tile_caches.insert(slice_id, TileCacheParams {
+        slice,
+        slice_flags,
+        spatial_node_index: scroll_root,
+        background_color,
+        shared_clip_node_id,
+        shared_clip_leaf_id,
+        virtual_surface_size: frame_builder_config.compositor_kind.get_virtual_surface_size(),
+        compositor_surface_count: prim_list.compositor_surface_count,
+    });
+
+    let pic_index = prim_store.pictures.alloc().init(PicturePrimitive::new_image(
+        Some(PictureCompositeMode::TileCache { slice_id }),
+        Picture3DContext::Out,
+        PrimitiveFlags::IS_BACKFACE_VISIBLE,
+        prim_list,
+        scroll_root,
+        RasterSpace::Screen,
+        PictureFlags::empty(),
+    ));
+
+    tile_cache_pictures.push(PictureIndex(pic_index));
+}
+
+/// Debug information about a set of picture cache slices, exposed via RenderResults
+#[derive(Debug)]
+#[cfg_attr(feature = "capture", derive(Serialize))]
+#[cfg_attr(feature = "replay", derive(Deserialize))]
+pub struct PictureCacheDebugInfo {
+    pub slices: FastHashMap<usize, SliceDebugInfo>,
+}
+
+impl PictureCacheDebugInfo {
+    pub fn new() -> Self {
+        PictureCacheDebugInfo {
+            slices: FastHashMap::default(),
+        }
+    }
+
+    /// Convenience method to retrieve a given slice. Deliberately panics
+    /// if the slice isn't present.
+    pub fn slice(&self, slice: usize) -> &SliceDebugInfo {
+        &self.slices[&slice]
+    }
+}
+
+impl Default for PictureCacheDebugInfo {
+    fn default() -> PictureCacheDebugInfo {
+        PictureCacheDebugInfo::new()
+    }
+}
+
+/// Debug information about a set of picture cache tiles, exposed via RenderResults
+#[derive(Debug)]
+#[cfg_attr(feature = "capture", derive(Serialize))]
+#[cfg_attr(feature = "replay", derive(Deserialize))]
+pub struct SliceDebugInfo {
+    pub tiles: FastHashMap<TileOffset, TileDebugInfo>,
+}
+
+impl SliceDebugInfo {
+    pub fn new() -> Self {
+        SliceDebugInfo {
+            tiles: FastHashMap::default(),
+        }
+    }
+
+    /// Convenience method to retrieve a given tile. Deliberately panics
+    /// if the tile isn't present.
+    pub fn tile(&self, x: i32, y: i32) -> &TileDebugInfo {
+        &self.tiles[&TileOffset::new(x, y)]
+    }
+}
+
+/// Debug information about a tile that was dirty and was rasterized
+#[derive(Debug, PartialEq)]
+#[cfg_attr(feature = "capture", derive(Serialize))]
+#[cfg_attr(feature = "replay", derive(Deserialize))]
+pub struct DirtyTileDebugInfo {
+    pub local_valid_rect: PictureRect,
+    pub local_dirty_rect: PictureRect,
+}
+
+/// Debug information about the state of a tile
+#[derive(Debug, PartialEq)]
+#[cfg_attr(feature = "capture", derive(Serialize))]
+#[cfg_attr(feature = "replay", derive(Deserialize))]
+pub enum TileDebugInfo {
+    /// Tile was occluded by a tile in front of it
+    Occluded,
+    /// Tile was culled (not visible in current display port)
+    Culled,
+    /// Tile was valid (no rasterization was done) and visible
+    Valid,
+    /// Tile was dirty, and was updated
+    Dirty(DirtyTileDebugInfo),
+}
+
+impl TileDebugInfo {
+    pub fn is_occluded(&self) -> bool {
+        match self {
+            TileDebugInfo::Occluded => true,
+            TileDebugInfo::Culled |
+            TileDebugInfo::Valid |
+            TileDebugInfo::Dirty(..) => false,
+        }
+    }
+
+    pub fn is_valid(&self) -> bool {
+        match self {
+            TileDebugInfo::Valid => true,
+            TileDebugInfo::Culled |
+            TileDebugInfo::Occluded |
+            TileDebugInfo::Dirty(..) => false,
+        }
+    }
+
+    pub fn is_culled(&self) -> bool {
+        match self {
+            TileDebugInfo::Culled => true,
+            TileDebugInfo::Valid |
+            TileDebugInfo::Occluded |
+            TileDebugInfo::Dirty(..) => false,
+        }
+    }
+
+    pub fn as_dirty(&self) -> &DirtyTileDebugInfo {
+        match self {
+            TileDebugInfo::Occluded |
+            TileDebugInfo::Culled |
+            TileDebugInfo::Valid => {
+                panic!("not a dirty tile!");
+            }
+            TileDebugInfo::Dirty(ref info) => {
+                info
+            }
+        }
+    }
+}