source/blender/draw/engines/eevee/shaders/effect_reflection_resolve_frag.glsl

@@ -103,6 +103,20 @@ void resolve_reflection_sample(int planar_index,
   weight_accum += weight;
 }
 
+/* NOTE(Metal): For Apple silicon GPUs executing this particular shader, by default, memory read
+ * pressure is high while ALU remains low. Packing the sample data into a smaller format balances
+ * this trade-off by reducing local shader register pressure and expensive memory look-ups into
+ * spilled local shader memory, resulting in an increase in performance of 20% for this shader. */
+#ifdef GPU_METAL
+#  define SAMPLE_STORAGE_TYPE uchar
+#  define pack_sample(x, y) uchar(((uchar(x + 2)) << uchar(3)) + (uchar(y + 2)))
+#  define unpack_sample(x) vec2((char(x) >> 3) - 2, (char(x) & 7) - 2)
+#else
+#  define SAMPLE_STORAGE_TYPE vec2
+#  define pack_sample(x, y) SAMPLE_STORAGE_TYPE(x, y)
+#  define unpack_sample(x) x
+#endif
+
 void raytrace_resolve(ClosureInputGlossy cl_in,
                       inout ClosureEvalGlossy cl_eval,
                       inout ClosureEvalCommon cl_common,
@@ -110,55 +124,55 @@ void raytrace_resolve(ClosureInputGlossy cl_in,
 {
   /* Note: Reflection samples declared in function scope to avoid per-thread memory pressure on
    * tile-based GPUs e.g. Apple Silicon. */
-  const vec2 resolve_sample_offsets[36] = vec2[36](
+  const SAMPLE_STORAGE_TYPE resolve_sample_offsets[36] = SAMPLE_STORAGE_TYPE[36](
       /* Set 1. */
       /* First Ring (2x2). */
-      vec2(0, 0),
+      pack_sample(0, 0),
       /* Second Ring (6x6). */
-      vec2(-1, 3),
-      vec2(1, 3),
-      vec2(-1, 1),
-      vec2(3, 1),
-      vec2(-2, 0),
-      vec2(3, 0),
-      vec2(2, -1),
-      vec2(1, -2),
+      pack_sample(-1, 3),
+      pack_sample(1, 3),
+      pack_sample(-1, 1),
+      pack_sample(3, 1),
+      pack_sample(-2, 0),
+      pack_sample(3, 0),
+      pack_sample(2, -1),
+      pack_sample(1, -2),
       /* Set 2. */
       /* First Ring (2x2). */
-      vec2(1, 1),
+      pack_sample(1, 1),
       /* Second Ring (6x6). */
-      vec2(-2, 3),
-      vec2(3, 3),
-      vec2(0, 2),
-      vec2(2, 2),
-      vec2(-2, -1),
-      vec2(1, -1),
-      vec2(0, -2),
-      vec2(3, -2),
+      pack_sample(-2, 3),
+      pack_sample(3, 3),
+      pack_sample(0, 2),
+      pack_sample(2, 2),
+      pack_sample(-2, -1),
+      pack_sample(1, -1),
+      pack_sample(0, -2),
+      pack_sample(3, -2),
       /* Set 3. */
       /* First Ring (2x2). */
-      vec2(0, 1),
+      pack_sample(0, 1),
       /* Second Ring (6x6). */
-      vec2(0, 3),
-      vec2(3, 2),
-      vec2(-2, 1),
-      vec2(2, 1),
-      vec2(-1, 0),
-      vec2(-2, -2),
-      vec2(0, -1),
-      vec2(2, -2),
+      pack_sample(0, 3),
+      pack_sample(3, 2),
+      pack_sample(-2, 1),
+      pack_sample(2, 1),
+      pack_sample(-1, 0),
+      pack_sample(-2, -2),
+      pack_sample(0, -1),
+      pack_sample(2, -2),
       /* Set 4. */
       /* First Ring (2x2). */
-      vec2(1, 0),
+      pack_sample(1, 0),
       /* Second Ring (6x6). */
-      vec2(2, 3),
-      vec2(-2, 2),
-      vec2(-1, 2),
-      vec2(1, 2),
-      vec2(2, 0),
-      vec2(-1, -1),
-      vec2(3, -1),
-      vec2(-1, -2));
+      pack_sample(2, 3),
+      pack_sample(-2, 2),
+      pack_sample(-1, 2),
+      pack_sample(1, 2),
+      pack_sample(2, 0),
+      pack_sample(-1, -1),
+      pack_sample(3, -1),
+      pack_sample(-1, -2));
 
   float roughness = cl_in.roughness;
 
@@ -208,7 +222,8 @@ void raytrace_resolve(ClosureInputGlossy cl_in,
       int sample_id = sample_pool * resolve_samples_count + i;
       vec2 texture_size = vec2(textureSize(hitBuffer, 0));
       vec2 sample_texel = texture_size * uvcoordsvar.xy * ssrUvScale;
-      vec2 sample_uv = (sample_texel + resolve_sample_offsets[sample_id]) / texture_size;
+      vec2 sample_uv = (sample_texel + unpack_sample(resolve_sample_offsets[sample_id])) /
+                       texture_size;
 
       resolve_reflection_sample(
           planar_index, sample_uv, vP, vN, vV, roughness_squared, cone_tan, weight_acc, ssr_accum);