Bug 1757588 - Reorganize the primitive instance flag bits. r=gw

The goal is to allow the brush flags to use more bits in a followup changes.Currently it uses all of its available 8 bits, this patch allows it to use up to 12.

Differential Revision: https://phabricator.services.mozilla.com/D140967

gfx/wr/webrender/res/brush.glsl

@@ -95,8 +95,8 @@ void brush_shader_main_vs(
     PictureTask pic_task,
     ClipArea clip_area
 ) {
-    int edge_flags = instance.flags & 0xff;
-    int brush_flags = (instance.flags >> 8) & 0xff;
+    int edge_flags = (instance.flags >> 12) & 0xf;
+    int brush_flags = instance.flags & 0xfff;
 
     // Fetch the segment of this brush primitive we are drawing.
     vec4 segment_data;

gfx/wr/webrender/src/gpu_types.rs

@@ -545,12 +545,15 @@ impl From<SplitCompositeInstance> for PrimitiveInstanceData {
 }
 
 bitflags! {
+    // Note: This can use up to 12 bits due to how it will
+    // be packed in the instance data.
+
     /// Flags that define how the common brush shader
     /// code should process this instance.
     #[cfg_attr(feature = "capture", derive(Serialize))]
     #[cfg_attr(feature = "replay", derive(Deserialize))]
     #[derive(MallocSizeOf)]
-    pub struct BrushFlags: u8 {
+    pub struct BrushFlags: u16 {
         /// Apply perspective interpolation to UVs
         const PERSPECTIVE_INTERPOLATION = 1;
         /// Do interpolation relative to segment rect,
@@ -590,8 +593,8 @@ impl From<BrushInstance> for PrimitiveInstanceData {
                 ((instance.render_task_address.0 as i32) << 16)
                 | instance.clip_task_address.0 as i32,
                 instance.segment_index
-                | ((instance.edge_flags.bits() as i32) << 16)
-                | ((instance.brush_flags.bits() as i32) << 24),
+                | ((instance.brush_flags.bits() as i32) << 16)
+                | ((instance.edge_flags.bits() as i32) << 28),
                 instance.resource_address,
             ]
         }

gfx/wr/webrender/src/segment.rs

@@ -60,6 +60,9 @@ use smallvec::SmallVec;
 const MAX_SEGMENTS: usize = 64;
 
 bitflags! {
+    // Note: This can use up to 4 bits due to how it will be packed in
+    // the instance data.
+
     /// Each bit of the edge AA mask is:
     /// 0, when the edge of the primitive needs to be considered for AA
     /// 1, when the edge of the segment needs to be considered for AA