1 files changed, 275 insertions, 0 deletions
diff --git a/gfx/wr/webrender/src/box_shadow.rs b/gfx/wr/webrender/src/box_shadow.rs
new file mode 100644
index 0000000000..ddc4d90854
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+++ b/gfx/wr/webrender/src/box_shadow.rs
@@ -0,0 +1,275 @@
+/* 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::{BorderRadius, BoxShadowClipMode, ClipMode, ColorF, PrimitiveKeyKind};
+use api::PropertyBinding;
+use api::units::*;
+use crate::clip::{ClipItemKey, ClipItemKeyKind, ClipChainId};
+use crate::scene_building::SceneBuilder;
+use crate::spatial_tree::SpatialNodeIndex;
+use crate::gpu_types::BoxShadowStretchMode;
+use crate::render_task_cache::RenderTaskCacheEntryHandle;
+use crate::internal_types::LayoutPrimitiveInfo;
+
+#[derive(Debug, Clone, MallocSizeOf)]
+#[cfg_attr(feature = "capture", derive(Serialize))]
+#[cfg_attr(feature = "replay", derive(Deserialize))]
+pub struct BoxShadowClipSource {
+    // Parameters that define the shadow and are constant.
+    pub shadow_radius: BorderRadius,
+    pub blur_radius: f32,
+    pub clip_mode: BoxShadowClipMode,
+    pub stretch_mode_x: BoxShadowStretchMode,
+    pub stretch_mode_y: BoxShadowStretchMode,
+
+    // The current cache key (in device-pixels), and handles
+    // to the cached clip region and blurred texture.
+    pub cache_key: Option<(DeviceIntSize, BoxShadowCacheKey)>,
+    pub cache_handle: Option<RenderTaskCacheEntryHandle>,
+
+    // Local-space size of the required render task size.
+    pub shadow_rect_alloc_size: LayoutSize,
+
+    // Local-space size of the required render task size without any downscaling
+    // applied. This is needed to stretch the shadow properly.
+    pub original_alloc_size: LayoutSize,
+
+    // The minimal shadow rect for the parameters above,
+    // used when drawing the shadow rect to be blurred.
+    pub minimal_shadow_rect: LayoutRect,
+
+    // Local space rect for the shadow to be drawn or
+    // stretched in the shadow primitive.
+    pub prim_shadow_rect: LayoutRect,
+}
+
+// The blur shader samples BLUR_SAMPLE_SCALE * blur_radius surrounding texels.
+pub const BLUR_SAMPLE_SCALE: f32 = 3.0;
+
+// Maximum blur radius for box-shadows (different than blur filters).
+// Taken from nsCSSRendering.cpp in Gecko.
+pub const MAX_BLUR_RADIUS: f32 = 300.;
+
+// A cache key that uniquely identifies a minimally sized
+// and blurred box-shadow rect that can be stored in the
+// texture cache and applied to clip-masks.
+#[derive(Debug, Clone, Eq, Hash, MallocSizeOf, PartialEq)]
+#[cfg_attr(feature = "capture", derive(Serialize))]
+#[cfg_attr(feature = "replay", derive(Deserialize))]
+pub struct BoxShadowCacheKey {
+    pub blur_radius_dp: i32,
+    pub clip_mode: BoxShadowClipMode,
+    // NOTE(emilio): Only the original allocation size needs to be in the cache
+    // key, since the actual size is derived from that.
+    pub original_alloc_size: DeviceIntSize,
+    pub br_top_left: DeviceIntSize,
+    pub br_top_right: DeviceIntSize,
+    pub br_bottom_right: DeviceIntSize,
+    pub br_bottom_left: DeviceIntSize,
+    pub device_pixel_scale: Au,
+}
+
+impl<'a> SceneBuilder<'a> {
+    pub fn add_box_shadow(
+        &mut self,
+        spatial_node_index: SpatialNodeIndex,
+        clip_chain_id: ClipChainId,
+        prim_info: &LayoutPrimitiveInfo,
+        box_offset: &LayoutVector2D,
+        color: ColorF,
+        mut blur_radius: f32,
+        spread_radius: f32,
+        border_radius: BorderRadius,
+        clip_mode: BoxShadowClipMode,
+    ) {
+        if color.a == 0.0 {
+            return;
+        }
+
+        // Inset shadows get smaller as spread radius increases.
+        let (spread_amount, prim_clip_mode) = match clip_mode {
+            BoxShadowClipMode::Outset => (spread_radius, ClipMode::ClipOut),
+            BoxShadowClipMode::Inset => (-spread_radius, ClipMode::Clip),
+        };
+
+        // Ensure the blur radius is somewhat sensible.
+        blur_radius = f32::min(blur_radius, MAX_BLUR_RADIUS);
+
+        // Adjust the border radius of the box shadow per CSS-spec.
+        let shadow_radius = adjust_border_radius_for_box_shadow(border_radius, spread_amount);
+
+        // Apply parameters that affect where the shadow rect
+        // exists in the local space of the primitive.
+        let shadow_rect = self.snap_rect(
+            &prim_info
+                .rect
+                .translate(*box_offset)
+                .inflate(spread_amount, spread_amount),
+            spatial_node_index,
+        );
+
+        // If blur radius is zero, we can use a fast path with
+        // no blur applied.
+        if blur_radius == 0.0 {
+            // Trivial reject of box-shadows that are not visible.
+            if box_offset.x == 0.0 && box_offset.y == 0.0 && spread_amount == 0.0 {
+                return;
+            }
+
+            let mut clips = Vec::with_capacity(2);
+            let (final_prim_rect, clip_radius) = match clip_mode {
+                BoxShadowClipMode::Outset => {
+                    if shadow_rect.is_empty() {
+                        return;
+                    }
+
+                    // TODO(gw): Add a fast path for ClipOut + zero border radius!
+                    clips.push(ClipItemKey {
+                        kind: ClipItemKeyKind::rounded_rect(
+                            prim_info.rect,
+                            border_radius,
+                            ClipMode::ClipOut,
+                        ),
+                    });
+
+                    (shadow_rect, shadow_radius)
+                }
+                BoxShadowClipMode::Inset => {
+                    if !shadow_rect.is_empty() {
+                        clips.push(ClipItemKey {
+                            kind: ClipItemKeyKind::rounded_rect(
+                                shadow_rect,
+                                shadow_radius,
+                                ClipMode::ClipOut,
+                            ),
+                        });
+                    }
+
+                    (prim_info.rect, border_radius)
+                }
+            };
+
+            clips.push(ClipItemKey {
+                kind: ClipItemKeyKind::rounded_rect(
+                    final_prim_rect,
+                    clip_radius,
+                    ClipMode::Clip,
+                ),
+            });
+
+            self.add_primitive(
+                spatial_node_index,
+                clip_chain_id,
+                &LayoutPrimitiveInfo::with_clip_rect(final_prim_rect, prim_info.clip_rect),
+                clips,
+                PrimitiveKeyKind::Rectangle {
+                    color: PropertyBinding::Value(color.into()),
+                },
+            );
+        } else {
+            // Normal path for box-shadows with a valid blur radius.
+            let blur_offset = (BLUR_SAMPLE_SCALE * blur_radius).ceil();
+            let mut extra_clips = vec![];
+
+            // Add a normal clip mask to clip out the contents
+            // of the surrounding primitive.
+            extra_clips.push(ClipItemKey {
+                kind: ClipItemKeyKind::rounded_rect(
+                    prim_info.rect,
+                    border_radius,
+                    prim_clip_mode,
+                ),
+            });
+
+            // Get the local rect of where the shadow will be drawn,
+            // expanded to include room for the blurred region.
+            let dest_rect = shadow_rect.inflate(blur_offset, blur_offset);
+
+            // Draw the box-shadow as a solid rect, using a box-shadow
+            // clip mask item.
+            let prim = PrimitiveKeyKind::Rectangle {
+                color: PropertyBinding::Value(color.into()),
+            };
+
+            // Create the box-shadow clip item.
+            let shadow_clip_source = ClipItemKey {
+                kind: ClipItemKeyKind::box_shadow(
+                    shadow_rect,
+                    shadow_radius,
+                    dest_rect,
+                    blur_radius,
+                    clip_mode,
+                ),
+            };
+
+            let prim_info = match clip_mode {
+                BoxShadowClipMode::Outset => {
+                    // Certain spread-radii make the shadow invalid.
+                    if shadow_rect.is_empty() {
+                        return;
+                    }
+
+                    // Add the box-shadow clip source.
+                    extra_clips.push(shadow_clip_source);
+
+                    // Outset shadows are expanded by the shadow
+                    // region from the original primitive.
+                    LayoutPrimitiveInfo::with_clip_rect(dest_rect, prim_info.clip_rect)
+                }
+                BoxShadowClipMode::Inset => {
+                    // If the inner shadow rect contains the prim
+                    // rect, no pixels will be shadowed.
+                    if border_radius.is_zero() && shadow_rect
+                        .inflate(-blur_radius, -blur_radius)
+                        .contains_rect(&prim_info.rect)
+                    {
+                        return;
+                    }
+
+                    // Inset shadows are still visible, even if the
+                    // inset shadow rect becomes invalid (they will
+                    // just look like a solid rectangle).
+                    if !shadow_rect.is_empty() {
+                        extra_clips.push(shadow_clip_source);
+                    }
+
+                    // Inset shadows draw inside the original primitive.
+                    prim_info.clone()
+                }
+            };
+
+            self.add_primitive(
+                spatial_node_index,
+                clip_chain_id,
+                &prim_info,
+                extra_clips,
+                prim,
+            );
+        }
+    }
+}
+
+fn adjust_border_radius_for_box_shadow(radius: BorderRadius, spread_amount: f32) -> BorderRadius {
+    BorderRadius {
+        top_left: adjust_corner_for_box_shadow(radius.top_left, spread_amount),
+        top_right: adjust_corner_for_box_shadow(radius.top_right, spread_amount),
+        bottom_right: adjust_corner_for_box_shadow(radius.bottom_right, spread_amount),
+        bottom_left: adjust_corner_for_box_shadow(radius.bottom_left, spread_amount),
+    }
+}
+
+fn adjust_corner_for_box_shadow(corner: LayoutSize, spread_amount: f32) -> LayoutSize {
+    LayoutSize::new(
+        adjust_radius_for_box_shadow(corner.width, spread_amount),
+        adjust_radius_for_box_shadow(corner.height, spread_amount),
+    )
+}
+
+fn adjust_radius_for_box_shadow(border_radius: f32, spread_amount: f32) -> f32 {
+    if border_radius > 0.0 {
+        (border_radius + spread_amount).max(0.0)
+    } else {
+        0.0
+    }
+}