1 files changed, 86 insertions, 0 deletions
diff --git a/gfx/wr/webrender/res/clip_shared.glsl b/gfx/wr/webrender/res/clip_shared.glsl
new file mode 100644
index 0000000000..924d6fdd1d
--- /dev/null
+++ b/gfx/wr/webrender/res/clip_shared.glsl
@@ -0,0 +1,86 @@
+/* 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/. */
+
+#include rect,render_task,gpu_cache,transform
+
+#ifdef WR_VERTEX_SHADER
+
+PER_INSTANCE in vec4 aClipDeviceArea;
+PER_INSTANCE in vec4 aClipOrigins;
+PER_INSTANCE in float aDevicePixelScale;
+PER_INSTANCE in ivec2 aTransformIds;
+
+struct ClipMaskInstanceCommon {
+    RectWithSize sub_rect;
+    vec2 task_origin;
+    vec2 screen_origin;
+    float device_pixel_scale;
+    int clip_transform_id;
+    int prim_transform_id;
+};
+
+ClipMaskInstanceCommon fetch_clip_item_common() {
+    ClipMaskInstanceCommon cmi;
+
+    cmi.sub_rect = RectWithSize(aClipDeviceArea.xy, aClipDeviceArea.zw);
+    cmi.task_origin = aClipOrigins.xy;
+    cmi.screen_origin = aClipOrigins.zw;
+    cmi.device_pixel_scale = aDevicePixelScale;
+    cmi.clip_transform_id = aTransformIds.x;
+    cmi.prim_transform_id = aTransformIds.y;
+
+    return cmi;
+}
+
+struct ClipVertexInfo {
+    vec4 local_pos;
+    RectWithSize clipped_local_rect;
+};
+
+RectWithSize intersect_rect(RectWithSize a, RectWithSize b) {
+    vec4 p = clamp(vec4(a.p0, a.p0 + a.size), b.p0.xyxy, b.p0.xyxy + b.size.xyxy);
+    return RectWithSize(p.xy, max(vec2(0.0), p.zw - p.xy));
+}
+
+
+// The transformed vertex function that always covers the whole clip area,
+// which is the intersection of all clip instances of a given primitive
+ClipVertexInfo write_clip_tile_vertex(RectWithSize local_clip_rect,
+                                      Transform prim_transform,
+                                      Transform clip_transform,
+                                      RectWithSize sub_rect,
+                                      vec2 task_origin,
+                                      vec2 screen_origin,
+                                      float device_pixel_scale) {
+    vec2 device_pos = screen_origin + sub_rect.p0 + aPosition.xy * sub_rect.size;
+    vec2 world_pos = device_pos / device_pixel_scale;
+
+    vec4 pos = prim_transform.m * vec4(world_pos, 0.0, 1.0);
+    pos.xyz /= pos.w;
+
+    vec4 p = get_node_pos(pos.xy, clip_transform);
+    vec4 local_pos = p * pos.w;
+
+    //TODO: Interpolate in clip space, where "local_pos.w" contains
+    // the W of the homogeneous transform *from* clip space into the world.
+    //    float interpolate_w = 1.0 / local_pos.w;
+    // This is problematic today, because the W<=0 hemisphere is going to be
+    // clipped, while we currently want this shader to fill out the whole rect.
+    // We can therefore simplify this when the clip construction is rewritten
+    // to only affect the areas touched by a clip.
+    vec4 vertex_pos = vec4(
+        task_origin + sub_rect.p0 + aPosition.xy * sub_rect.size,
+        0.0,
+        1.0
+    );
+
+    gl_Position = uTransform * vertex_pos;
+
+    init_transform_vs(vec4(local_clip_rect.p0, local_clip_rect.p0 + local_clip_rect.size));
+
+    ClipVertexInfo vi = ClipVertexInfo(local_pos, local_clip_rect);
+    return vi;
+}
+
+#endif //WR_VERTEX_SHADER