Metal: GLSL shader compatibility 3rd pass

Undefined behaviour for divergent control-flow fixes, replacement for partial vector references, and resolution of a number of calculation precision issues occuring on macOS.

Authored by Apple: Michael Parkin-White

Ref: T96261

Reviewed By: fclem

Differential Revision: https://developer.blender.org/D14437

3 files changed, 33 insertions, 7 deletions

diff --git a/source/blender/draw/intern/shaders/common_hair_lib.glsl b/source/blender/draw/intern/shaders/common_hair_lib.glsl
index 6a8f1132e1b..ff52b483d77 100644
--- a/source/blender/draw/intern/shaders/common_hair_lib.glsl
+++ b/source/blender/draw/intern/shaders/common_hair_lib.glsl
@@ -211,6 +211,11 @@ void hair_get_pos_tan_binor_time(bool is_persp,
 
     wpos += wbinor * thick_time * scale;
   }
+  else {
+    /* Note: Ensures 'hairThickTime' is initialised -
+     * avoids undefined behaviour on certain macOS configurations. */
+    thick_time = 0.0;
+  }
 }
 
 float hair_get_customdata_float(const samplerBuffer cd_buf)
diff --git a/source/blender/draw/intern/shaders/common_hair_refine_vert.glsl b/source/blender/draw/intern/shaders/common_hair_refine_vert.glsl
index 371d43827b9..2eccae5bceb 100644
--- a/source/blender/draw/intern/shaders/common_hair_refine_vert.glsl
+++ b/source/blender/draw/intern/shaders/common_hair_refine_vert.glsl
@@ -18,7 +18,7 @@ void main(void)
   vec4 weights = hair_get_weights_cardinal(interp_time);
   finalColor = hair_interp_data(data0, data1, data2, data3, weights);
 
-#ifdef TF_WORKAROUND
+#if defined(TF_WORKAROUND)
   int id = gl_VertexID - idOffset;
   gl_Position.x = ((float(id % targetWidth) + 0.5) / float(targetWidth)) * 2.0 - 1.0;
   gl_Position.y = ((float(id / targetWidth) + 0.5) / float(targetHeight)) * 2.0 - 1.0;
@@ -26,5 +26,10 @@ void main(void)
   gl_Position.w = 1.0;
 
   gl_PointSize = 1.0;
+#else
+#  ifdef GPU_METAL
+  /* Metal still expects an output position for TF shaders. */
+  gl_Position = vec4(0.0, 0.0, 0.0, 1.0);
+#  endif
 #endif
 }
diff --git a/source/blender/draw/intern/shaders/common_smaa_lib.glsl b/source/blender/draw/intern/shaders/common_smaa_lib.glsl
index 73f65fb0799..dbc4c998b34 100644
--- a/source/blender/draw/intern/shaders/common_smaa_lib.glsl
+++ b/source/blender/draw/intern/shaders/common_smaa_lib.glsl
@@ -569,7 +569,7 @@ SamplerState PointSampler
 #    define SMAAGather(tex, coord) tex.Gather(LinearSampler, coord, 0)
 #  endif
 #endif
-#if defined(SMAA_GLSL_3) || defined(SMAA_GLSL_4)
+#if defined(SMAA_GLSL_3) || defined(SMAA_GLSL_4) || defined(GPU_METAL)
 #  define SMAATexture2D(tex) sampler2D tex
 #  define SMAATexturePass2D(tex) tex
 #  define SMAASampleLevelZero(tex, coord) textureLod(tex, coord, 0.0)
@@ -641,14 +641,14 @@ float2 SMAACalculatePredicatedThreshold(float2 texcoord,
  */
 void SMAAMovc(bool2 cond, inout float2 variable, float2 value)
 {
-  SMAA_FLATTEN if (cond.x) variable.x = value.x;
-  SMAA_FLATTEN if (cond.y) variable.y = value.y;
+  /* Use select function (select(genType A, genType B, genBType cond)). */
+  variable = select(variable, value, cond);
 }
 
 void SMAAMovc(bool4 cond, inout float4 variable, float4 value)
 {
-  SMAAMovc(cond.xy, variable.xy, value.xy);
-  SMAAMovc(cond.zw, variable.zw, value.zw);
+  /* Use select function (select(genType A, genType B, genBType cond)). */
+  variable = select(variable, value, cond);
 }
 
 #if SMAA_INCLUDE_VS
@@ -1281,7 +1281,15 @@ float4 SMAABlendingWeightCalculationPS(float2 texcoord,
 
       // Fix corners:
       coords.y = texcoord.y;
-      SMAADetectHorizontalCornerPattern(SMAATexturePass2D(edgesTex), weights.rg, coords.xyzy, d);
+
+#  ifdef GPU_METAL
+      /* Partial vector references are unsupported in MSL. */
+      vec2 _weights = weights.rg;
+      SMAADetectHorizontalCornerPattern(SMAATexturePass2D(edgesTex), _weights, coords.xyzy, d);
+      weights.rg = _weights;
+#  else
+    SMAADetectHorizontalCornerPattern(SMAATexturePass2D(edgesTex), weights.rg, coords.xyzy, d);
+#  endif
 
 #  if !defined(SMAA_DISABLE_DIAG_DETECTION)
     }
@@ -1324,7 +1332,15 @@ float4 SMAABlendingWeightCalculationPS(float2 texcoord,
 
     // Fix corners:
     coords.x = texcoord.x;
+
+#  ifdef GPU_METAL
+    /* Partial vector references are unsupported in MSL. */
+    vec2 _weights = weights.ba;
+    SMAADetectVerticalCornerPattern(SMAATexturePass2D(edgesTex), _weights, coords.xyxz, d);
+    weights.ba = _weights;
+#  else
     SMAADetectVerticalCornerPattern(SMAATexturePass2D(edgesTex), weights.ba, coords.xyxz, d);
+#  endif
   }
 
   return weights;