Metal: Make GLSL shader source MSL compliant also

Metal shading language follows the C++ 14 standard and in some cases requires a greater level of explicitness than GLSL. There are also some small language differences:

- Explicit type-casts (C++ requirements)
- Explicit constant values (C++ requirements, e.g. floating point values using 0.0 instead of 0).
- Metal/OpenGL compatibility paths
- GLSL Function prototypes
- Explicit accessors for vector types when sampling textures.

Authored by Apple: Michael Parkin-White

Ref T96261

Reviewed By: fclem

Maniphest Tasks: T96261

Differential Revision: https://developer.blender.org/D14378

37 files changed, 120 insertions, 50 deletions

diff --git a/source/blender/draw/engines/eevee/shaders/closure_eval_glossy_lib.glsl b/source/blender/draw/engines/eevee/shaders/closure_eval_glossy_lib.glsl
index 584aacc9e19..ddc6a0b9661 100644
--- a/source/blender/draw/engines/eevee/shaders/closure_eval_glossy_lib.glsl
+++ b/source/blender/draw/engines/eevee/shaders/closure_eval_glossy_lib.glsl
@@ -26,10 +26,13 @@ struct ClosureEvalGlossy {
 
 #ifdef STEP_RESOLVE /* SSR */
 /* Prototype. */
+#  ifndef GPU_METAL
+/* MSL does not require prototypes. */
 void raytrace_resolve(ClosureInputGlossy cl_in,
                       inout ClosureEvalGlossy cl_eval,
                       inout ClosureEvalCommon cl_common,
                       inout ClosureOutputGlossy cl_out);
+#  endif
 #endif
 
 ClosureEvalGlossy closure_Glossy_eval_init(inout ClosureInputGlossy cl_in,
diff --git a/source/blender/draw/engines/eevee/shaders/closure_type_lib.glsl b/source/blender/draw/engines/eevee/shaders/closure_type_lib.glsl
index f66f45635f4..fefc8743691 100644
--- a/source/blender/draw/engines/eevee/shaders/closure_type_lib.glsl
+++ b/source/blender/draw/engines/eevee/shaders/closure_type_lib.glsl
@@ -32,8 +32,10 @@ struct Closure {
 #endif
 };
 
+#ifndef GPU_METAL
 /* Prototype */
 Closure nodetree_exec(void);
+#endif
 
 /* clang-format off */
 /* Avoid multi-line defines. */
diff --git a/source/blender/draw/engines/eevee/shaders/effect_bloom_frag.glsl b/source/blender/draw/engines/eevee/shaders/effect_bloom_frag.glsl
index 9d9d7beb3cb..bdcc0a2ba93 100644
--- a/source/blender/draw/engines/eevee/shaders/effect_bloom_frag.glsl
+++ b/source/blender/draw/engines/eevee/shaders/effect_bloom_frag.glsl
@@ -150,7 +150,7 @@ vec4 step_blit(void)
   float br = max_v3(m);
 
   /* Under-threshold part: quadratic curve */
-  float rq = clamp(br - curveThreshold.x, 0, curveThreshold.y);
+  float rq = clamp(br - curveThreshold.x, 0.0, curveThreshold.y);
   rq = curveThreshold.z * rq * rq;
 
   /* Combine and apply the brightness response curve. */
diff --git a/source/blender/draw/engines/eevee/shaders/effect_dof_resolve_frag.glsl b/source/blender/draw/engines/eevee/shaders/effect_dof_resolve_frag.glsl
index 57027c71156..688ae4915e1 100644
--- a/source/blender/draw/engines/eevee/shaders/effect_dof_resolve_frag.glsl
+++ b/source/blender/draw/engines/eevee/shaders/effect_dof_resolve_frag.glsl
@@ -142,7 +142,7 @@ void dof_resolve_load_layer(sampler2D color_tex,
                             out float out_weight)
 {
   vec2 pixel_co = gl_FragCoord.xy / 2.0;
-  vec2 uv = pixel_co / textureSize(color_tex, 0).xy;
+  vec2 uv = pixel_co / vec2(textureSize(color_tex, 0).xy);
   out_color = textureLod(color_tex, uv, 0.0);
   out_weight = textureLod(weight_tex, uv, 0.0).r;
 }
diff --git a/source/blender/draw/engines/eevee/shaders/effect_dof_scatter_vert.glsl b/source/blender/draw/engines/eevee/shaders/effect_dof_scatter_vert.glsl
index b05223e755d..51a351babd3 100644
--- a/source/blender/draw/engines/eevee/shaders/effect_dof_scatter_vert.glsl
+++ b/source/blender/draw/engines/eevee/shaders/effect_dof_scatter_vert.glsl
@@ -95,7 +95,7 @@ void main()
 
   weights = dof_layer_weight(cocs) * dof_sample_weight(cocs);
   /* Filter NaNs. */
-  weights = mix(weights, vec4(0.0), equal(cocs, vec4(0.0)));
+  weights = select(weights, vec4(0.0), equal(cocs, vec4(0.0)));
 
   color1 = colors[0] * weights[0];
   color2 = colors[1] * weights[1];
diff --git a/source/blender/draw/engines/eevee/shaders/effect_dof_setup_frag.glsl b/source/blender/draw/engines/eevee/shaders/effect_dof_setup_frag.glsl
index 235145b221b..178ef46862b 100644
--- a/source/blender/draw/engines/eevee/shaders/effect_dof_setup_frag.glsl
+++ b/source/blender/draw/engines/eevee/shaders/effect_dof_setup_frag.glsl
@@ -54,12 +54,12 @@ void main()
   bvec4 focus = lessThanEqual(cocs, vec4(0.5));
   if (any(defocus) && any(focus)) {
     /* For the same reason as in the flatten pass. This is a case we cannot optimize for. */
-    cocs = mix(cocs, vec4(DOF_TILE_MIXED), focus);
-    cocs = mix(cocs, vec4(DOF_TILE_MIXED), defocus);
+    cocs = select(cocs, vec4(DOF_TILE_MIXED), focus);
+    cocs = select(cocs, vec4(DOF_TILE_MIXED), defocus);
   }
   else {
-    cocs = mix(cocs, vec4(DOF_TILE_FOCUS), focus);
-    cocs = mix(cocs, vec4(DOF_TILE_DEFOCUS), defocus);
+    cocs = select(cocs, vec4(DOF_TILE_FOCUS), focus);
+    cocs = select(cocs, vec4(DOF_TILE_DEFOCUS), defocus);
   }
   outCoc.y = max_v4(cocs);
 }
diff --git a/source/blender/draw/engines/eevee/shaders/effect_minmaxz_frag.glsl b/source/blender/draw/engines/eevee/shaders/effect_minmaxz_frag.glsl
index ce455123987..aaf673eecd2 100644
--- a/source/blender/draw/engines/eevee/shaders/effect_minmaxz_frag.glsl
+++ b/source/blender/draw/engines/eevee/shaders/effect_minmaxz_frag.glsl
@@ -38,7 +38,7 @@ uniform vec2 texelSize;
 
 /* On some AMD card / driver combination, it is needed otherwise,
  * the shader does not write anything. */
-#if defined(GPU_INTEL) || defined(GPU_ATI)
+#if (defined(GPU_INTEL) || defined(GPU_ATI)) && defined(GPU_OPENGL)
 out vec4 fragColor;
 #endif
 
@@ -68,9 +68,14 @@ void main()
   float val = minmax4(samp.x, samp.y, samp.z, samp.w);
 #endif
 
-#if defined(GPU_INTEL) || defined(GPU_ATI)
+#if (defined(GPU_INTEL) || defined(GPU_ATI)) && defined(GPU_OPENGL)
   /* Use color format instead of 24bit depth texture */
   fragColor = vec4(val);
 #endif
+
+#if !(defined(GPU_INTEL) && defined(GPU_OPENGL))
+  /* If using Intel workaround, do not write out depth as there will be no depth target and this is
+   * invalid. */
   gl_FragDepth = val;
+#endif
 }
diff --git a/source/blender/draw/engines/eevee/shaders/effect_reflection_trace_frag.glsl b/source/blender/draw/engines/eevee/shaders/effect_reflection_trace_frag.glsl
index f4ff28eaee4..c9010749060 100644
--- a/source/blender/draw/engines/eevee/shaders/effect_reflection_trace_frag.glsl
+++ b/source/blender/draw/engines/eevee/shaders/effect_reflection_trace_frag.glsl
@@ -60,11 +60,11 @@ void main()
   vec3 P = transform_point(ViewMatrixInverse, vP);
   vec3 vV = viewCameraVec(vP);
   vec3 V = cameraVec(P);
-  vec3 vN = normal_decode(texture(normalBuffer, uvs, 0).rg, vV);
+  vec3 vN = normal_decode(textureLod(normalBuffer, uvs, 0.0).rg, vV);
   vec3 N = transform_direction(ViewMatrixInverse, vN);
 
   /* Retrieve pixel data */
-  vec4 speccol_roughness = texture(specroughBuffer, uvs, 0).rgba;
+  vec4 speccol_roughness = textureLod(specroughBuffer, uvs, 0.0).rgba;
 
   /* Early out */
   if (dot(speccol_roughness.rgb, vec3(1.0)) == 0.0) {
diff --git a/source/blender/draw/engines/eevee/shaders/effect_velocity_tile_frag.glsl b/source/blender/draw/engines/eevee/shaders/effect_velocity_tile_frag.glsl
index 300477570d0..fc8091161d7 100644
--- a/source/blender/draw/engines/eevee/shaders/effect_velocity_tile_frag.glsl
+++ b/source/blender/draw/engines/eevee/shaders/effect_velocity_tile_frag.glsl
@@ -74,7 +74,7 @@ bool neighbor_affect_this_tile(ivec2 offset, vec2 velocity)
    * offset. If the offset coordinate is zero then
    * velocity is irrelevant.
    */
-  vec2 point = sign(offset * velocity);
+  vec2 point = sign(vec2(offset) * velocity);
 
   float dist = (point.x + point.y);
   /**
diff --git a/source/blender/draw/engines/eevee/shaders/lightprobe_lib.glsl b/source/blender/draw/engines/eevee/shaders/lightprobe_lib.glsl
index 84626eac4cf..e1035af37be 100644
--- a/source/blender/draw/engines/eevee/shaders/lightprobe_lib.glsl
+++ b/source/blender/draw/engines/eevee/shaders/lightprobe_lib.glsl
@@ -289,7 +289,7 @@ vec3 probe_evaluate_grid(GridData gd, vec3 P, vec3 N, vec3 localpos)
     weight += prbIrradianceSmooth;
 
     /* Trilinear weights */
-    vec3 trilinear = mix(1.0 - trilinear_weight, trilinear_weight, offset);
+    vec3 trilinear = mix(1.0 - trilinear_weight, trilinear_weight, vec3(offset));
     weight *= trilinear.x * trilinear.y * trilinear.z;
 
     /* Avoid zero weight */
diff --git a/source/blender/draw/engines/eevee/shaders/lightprobe_planar_downsample_frag.glsl b/source/blender/draw/engines/eevee/shaders/lightprobe_planar_downsample_frag.glsl
index cf44a04b707..5674e464f4c 100644
--- a/source/blender/draw/engines/eevee/shaders/lightprobe_planar_downsample_frag.glsl
+++ b/source/blender/draw/engines/eevee/shaders/lightprobe_planar_downsample_frag.glsl
@@ -16,11 +16,11 @@ void main()
 {
 #if 0
   /* Reconstructing Target uvs like this avoid missing pixels if NPO2 */
-  vec2 uvs = gl_FragCoord.xy * 2.0 / vec2(textureSize(source, 0));
+  vec2 uvs = gl_FragCoord.xy * 2.0 / vec2(textureSize(source, 0).xy);
 
   FragColor = textureLod(source, vec3(uvs, layer), 0.0);
 #else
-  vec2 texel_size = 1.0 / vec2(textureSize(source, 0));
+  vec2 texel_size = 1.0 / vec2(textureSize(source, 0).xy);
   vec2 uvs = gl_FragCoord.xy * 2.0 * texel_size;
   vec4 ofs = texel_size.xyxy * vec4(0.75, 0.75, -0.75, -0.75);
 
diff --git a/source/blender/draw/engines/eevee/shaders/volumetric_frag.glsl b/source/blender/draw/engines/eevee/shaders/volumetric_frag.glsl
index 25661a0d731..9f1afc4767c 100644
--- a/source/blender/draw/engines/eevee/shaders/volumetric_frag.glsl
+++ b/source/blender/draw/engines/eevee/shaders/volumetric_frag.glsl
@@ -31,7 +31,7 @@ layout(location = 3) out vec4 volumePhase;
 
 void main()
 {
-  ivec3 volume_cell = ivec3(gl_FragCoord.xy, slice);
+  ivec3 volume_cell = ivec3(ivec2(gl_FragCoord.xy), slice);
   vec3 ndc_cell = volume_to_ndc((vec3(volume_cell) + volJitter.xyz) * volInvTexSize.xyz);
 
   viewPosition = get_view_space_from_depth(ndc_cell.xy, ndc_cell.z);
diff --git a/source/blender/draw/engines/eevee/shaders/volumetric_integration_frag.glsl b/source/blender/draw/engines/eevee/shaders/volumetric_integration_frag.glsl
index 12b7d8acbea..11f57c0a82e 100644
--- a/source/blender/draw/engines/eevee/shaders/volumetric_integration_frag.glsl
+++ b/source/blender/draw/engines/eevee/shaders/volumetric_integration_frag.glsl
@@ -52,7 +52,7 @@ void main()
   ivec2 texco = ivec2(gl_FragCoord.xy);
 #endif
   for (int i = 0; i <= slice; i++) {
-    ivec3 volume_cell = ivec3(gl_FragCoord.xy, i);
+    ivec3 volume_cell = ivec3(ivec2(gl_FragCoord.xy), i);
 
     vec3 Lscat = texelFetch(volumeScattering, volume_cell, 0).rgb;
     vec3 s_extinction = texelFetch(volumeExtinction, volume_cell, 0).rgb;
diff --git a/source/blender/draw/engines/eevee/shaders/volumetric_scatter_frag.glsl b/source/blender/draw/engines/eevee/shaders/volumetric_scatter_frag.glsl
index dc755aeab8b..df3f92966e6 100644
--- a/source/blender/draw/engines/eevee/shaders/volumetric_scatter_frag.glsl
+++ b/source/blender/draw/engines/eevee/shaders/volumetric_scatter_frag.glsl
@@ -22,7 +22,7 @@ layout(location = 1) out vec4 outTransmittance;
 
 void main()
 {
-  ivec3 volume_cell = ivec3(gl_FragCoord.xy, slice);
+  ivec3 volume_cell = ivec3(ivec2(gl_FragCoord.xy), slice);
 
   /* Emission */
   outScattering = texelFetch(volumeEmission, volume_cell, 0);
diff --git a/source/blender/draw/engines/overlay/shaders/background_frag.glsl b/source/blender/draw/engines/overlay/shaders/background_frag.glsl
index 52052d414f8..19313c0415b 100644
--- a/source/blender/draw/engines/overlay/shaders/background_frag.glsl
+++ b/source/blender/draw/engines/overlay/shaders/background_frag.glsl
@@ -38,8 +38,8 @@ void main()
    * This removes the alpha channel and put the background behind reference images
    * while masking the reference images by the render alpha.
    */
-  float alpha = texture(colorBuffer, uvcoordsvar.st).a;
-  float depth = texture(depthBuffer, uvcoordsvar.st).r;
+  float alpha = texture(colorBuffer, uvcoordsvar.xy).a;
+  float depth = texture(depthBuffer, uvcoordsvar.xy).r;
 
   vec3 bg_col;
   vec3 col_high;
diff --git a/source/blender/draw/engines/overlay/shaders/outline_detect_frag.glsl b/source/blender/draw/engines/overlay/shaders/outline_detect_frag.glsl
index 0e4757f8ea8..19d54a57479 100644
--- a/source/blender/draw/engines/overlay/shaders/outline_detect_frag.glsl
+++ b/source/blender/draw/engines/overlay/shaders/outline_detect_frag.glsl
@@ -169,7 +169,7 @@ void diag_dir(bvec4 edges1, bvec4 edges2, out vec2 line_start, out vec2 line_end
 
 void main()
 {
-  uint ref = textureLod(outlineId, uvcoordsvar.st, 0.0).r;
+  uint ref = textureLod(outlineId, uvcoordsvar.xy, 0.0).r;
   uint ref_col = ref;
 
   vec2 uvs = gl_FragCoord.xy * sizeViewportInv.xy;
diff --git a/source/blender/draw/engines/overlay/shaders/volume_gridlines_vert.glsl b/source/blender/draw/engines/overlay/shaders/volume_gridlines_vert.glsl
index f714646fe40..507beb8a418 100644
--- a/source/blender/draw/engines/overlay/shaders/volume_gridlines_vert.glsl
+++ b/source/blender/draw/engines/overlay/shaders/volume_gridlines_vert.glsl
@@ -53,7 +53,7 @@ vec4 flag_to_color(uint flag)
   if (bool(flag & uint(16))) {
     color.rgb += vec3(0.9, 0.3, 0.0); /* orange */
   }
-  if (color.rgb == vec3(0.0)) {
+  if (is_zero(color.rgb)) {
     color.rgb += vec3(0.5, 0.0, 0.0); /* medium red */
   }
   return color;
diff --git a/source/blender/draw/engines/workbench/shaders/workbench_effect_cavity_frag.glsl b/source/blender/draw/engines/workbench/shaders/workbench_effect_cavity_frag.glsl
index 59222b588a0..7704e7ed0b7 100644
--- a/source/blender/draw/engines/workbench/shaders/workbench_effect_cavity_frag.glsl
+++ b/source/blender/draw/engines/workbench/shaders/workbench_effect_cavity_frag.glsl
@@ -9,11 +9,11 @@ void main()
   float cavity = 0.0, edges = 0.0, curvature = 0.0;
 
 #ifdef USE_CAVITY
-  cavity_compute(uvcoordsvar.st, depthBuffer, normalBuffer, cavity, edges);
+  cavity_compute(uvcoordsvar.xy, depthBuffer, normalBuffer, cavity, edges);
 #endif
 
 #ifdef USE_CURVATURE
-  curvature_compute(uvcoordsvar.st, objectIdBuffer, normalBuffer, curvature);
+  curvature_compute(uvcoordsvar.xy, objectIdBuffer, normalBuffer, curvature);
 #endif
 
   float final_cavity_factor = clamp((1.0 - cavity) * (1.0 + edges) * (1.0 + curvature), 0.0, 4.0);
diff --git a/source/blender/draw/engines/workbench/shaders/workbench_merge_infront_frag.glsl b/source/blender/draw/engines/workbench/shaders/workbench_merge_infront_frag.glsl
index ae564435258..30daca6b7e3 100644
--- a/source/blender/draw/engines/workbench/shaders/workbench_merge_infront_frag.glsl
+++ b/source/blender/draw/engines/workbench/shaders/workbench_merge_infront_frag.glsl
@@ -1,7 +1,7 @@
 
 void main()
 {
-  float depth = texture(depthBuffer, uvcoordsvar.st).r;
+  float depth = texture(depthBuffer, uvcoordsvar.xy).r;
   /* Fix issues with Intel drivers (see T80023). */
   fragColor = vec4(0.0);
   /* Discard background pixels. */
diff --git a/source/blender/draw/engines/workbench/shaders/workbench_transparent_resolve_frag.glsl b/source/blender/draw/engines/workbench/shaders/workbench_transparent_resolve_frag.glsl
index a2c45d2f8e3..35bea830bac 100644
--- a/source/blender/draw/engines/workbench/shaders/workbench_transparent_resolve_frag.glsl
+++ b/source/blender/draw/engines/workbench/shaders/workbench_transparent_resolve_frag.glsl
@@ -9,8 +9,8 @@ void main()
   /* Revealage is actually stored in transparentAccum alpha channel.
    * This is a workaround to older hardware not having separate blend equation per render target.
    */
-  vec4 trans_accum = texture(transparentAccum, uvcoordsvar.st);
-  float trans_weight = texture(transparentRevealage, uvcoordsvar.st).r;
+  vec4 trans_accum = texture(transparentAccum, uvcoordsvar.xy);
+  float trans_weight = texture(transparentRevealage, uvcoordsvar.xy).r;
   float trans_reveal = trans_accum.a;
 
   /* Listing 4 */
diff --git a/source/blender/draw/engines/workbench/shaders/workbench_volume_frag.glsl b/source/blender/draw/engines/workbench/shaders/workbench_volume_frag.glsl
index 076f6e80104..4ff281ccd29 100644
--- a/source/blender/draw/engines/workbench/shaders/workbench_volume_frag.glsl
+++ b/source/blender/draw/engines/workbench/shaders/workbench_volume_frag.glsl
@@ -94,7 +94,7 @@ vec4 flag_to_color(uint flag)
   if (bool(flag & uint(16))) {
     color.rgb += vec3(0.9, 0.3, 0.0); /* orange */
   }
-  if (color.rgb == vec3(0.0)) {
+  if (is_zero(color.rgb)) {
     color.rgb += vec3(0.5, 0.0, 0.0); /* medium red */
   }
   return color;
diff --git a/source/blender/draw/intern/shaders/common_hair_lib.glsl b/source/blender/draw/intern/shaders/common_hair_lib.glsl
index ed8b8aeb849..7f94b7ea1c1 100644
--- a/source/blender/draw/intern/shaders/common_hair_lib.glsl
+++ b/source/blender/draw/intern/shaders/common_hair_lib.glsl
@@ -158,7 +158,7 @@ float hair_shaperadius(float shape, float root, float tip, float time)
   return (radius * (root - tip)) + tip;
 }
 
-#  ifdef OS_MAC
+#  if defined(OS_MAC) && defined(GPU_OPENGL)
 in float dummy;
 #  endif
 
@@ -178,7 +178,7 @@ void hair_get_pos_tan_binor_time(bool is_persp,
   wpos = data.point_position;
   time = data.point_time;
 
-#  ifdef OS_MAC
+#  if defined(OS_MAC) && defined(GPU_OPENGL)
   /* Generate a dummy read to avoid the driver bug with shaders having no
    * vertex reads on macOS (T60171) */
   wpos.y += dummy * 0.0;
diff --git a/source/blender/draw/intern/shaders/common_math_geom_lib.glsl b/source/blender/draw/intern/shaders/common_math_geom_lib.glsl
index 7b701d1d81b..6d4452c18c8 100644
--- a/source/blender/draw/intern/shaders/common_math_geom_lib.glsl
+++ b/source/blender/draw/intern/shaders/common_math_geom_lib.glsl
@@ -86,7 +86,7 @@ float line_unit_box_intersect_dist(vec3 lineorigin, vec3 linedirection)
 float line_unit_box_intersect_dist_safe(vec3 lineorigin, vec3 linedirection)
 {
   vec3 safe_linedirection = max(vec3(1e-8), abs(linedirection)) *
-                            mix(vec3(1.0), -vec3(1.0), lessThan(linedirection, vec3(0.0)));
+                            select(vec3(1.0), -vec3(1.0), lessThan(linedirection, vec3(0.0)));
   return line_unit_box_intersect_dist(lineorigin, safe_linedirection);
 }
 
diff --git a/source/blender/draw/intern/shaders/common_math_lib.glsl b/source/blender/draw/intern/shaders/common_math_lib.glsl
index 1701056cbb7..4d0ffaeb40f 100644
--- a/source/blender/draw/intern/shaders/common_math_lib.glsl
+++ b/source/blender/draw/intern/shaders/common_math_lib.glsl
@@ -84,9 +84,9 @@ float avg(vec3 v) { return dot(vec3(1.0 / 3.0), v); }
 float avg(vec4 v) { return dot(vec4(1.0 / 4.0), v); }
 
 float safe_rcp(float a) { return (a != 0.0) ? (1.0 / a) : 0.0; }
-vec2 safe_rcp(vec2 a) { return mix(vec2(0.0), (1.0 / a), notEqual(a, vec2(0.0))); }
-vec3 safe_rcp(vec3 a) { return mix(vec3(0.0), (1.0 / a), notEqual(a, vec3(0.0))); }
-vec4 safe_rcp(vec4 a) { return mix(vec4(0.0), (1.0 / a), notEqual(a, vec4(0.0))); }
+vec2 safe_rcp(vec2 a) { return select(vec2(0.0), (1.0 / a), notEqual(a, vec2(0.0))); }
+vec3 safe_rcp(vec3 a) { return select(vec3(0.0), (1.0 / a), notEqual(a, vec3(0.0))); }
+vec4 safe_rcp(vec4 a) { return select(vec4(0.0), (1.0 / a), notEqual(a, vec4(0.0))); }
 
 float safe_sqrt(float a) { return sqrt(max(a, 0.0)); }
 
diff --git a/source/blender/draw/intern/shaders/common_view_lib.glsl b/source/blender/draw/intern/shaders/common_view_lib.glsl
index 2ac157ad208..6c58752c8bb 100644
--- a/source/blender/draw/intern/shaders/common_view_lib.glsl
+++ b/source/blender/draw/intern/shaders/common_view_lib.glsl
@@ -174,7 +174,7 @@ flat in int resourceIDFrag;
 
 /* Breaking this across multiple lines causes issues for some older GLSL compilers. */
 /* clang-format off */
-#if !defined(GPU_INTEL) && !defined(GPU_DEPRECATED_AMD_DRIVER) && !defined(OS_MAC) && !defined(INSTANCED_ATTR) && !defined(DRW_LEGACY_MODEL_MATRIX)
+#if !defined(GPU_INTEL) && !defined(GPU_DEPRECATED_AMD_DRIVER) && (!defined(OS_MAC) || defined(GPU_METAL)) && !defined(INSTANCED_ATTR) && !defined(DRW_LEGACY_MODEL_MATRIX)
 /* clang-format on */
 
 /* Temporary until we fully make the switch. */
@@ -251,7 +251,7 @@ uniform mat4 ModelMatrixInverse;
 
 /* Due to some shader compiler bug, we somewhat need to access gl_VertexID
  * to make vertex shaders work. even if it's actually dead code. */
-#ifdef GPU_INTEL
+#if defined(GPU_INTEL) && defined(GPU_OPENGL)
 #  define GPU_INTEL_VERTEX_SHADER_WORKAROUND gl_Position.x = float(gl_VertexID);
 #else
 #  define GPU_INTEL_VERTEX_SHADER_WORKAROUND
diff --git a/source/blender/gpu/CMakeLists.txt b/source/blender/gpu/CMakeLists.txt
index 6c795aba560..c28b51de8ac 100644
--- a/source/blender/gpu/CMakeLists.txt
+++ b/source/blender/gpu/CMakeLists.txt
@@ -210,6 +210,7 @@ endif()
 
 set(GLSL_SRC
   GPU_shader_shared.h
+  shaders/opengl/glsl_shader_defines.glsl
 
   shaders/gpu_shader_depth_only_frag.glsl
   shaders/gpu_shader_uniform_color_frag.glsl
diff --git a/source/blender/gpu/intern/gpu_shader.cc b/source/blender/gpu/intern/gpu_shader.cc
index ac8e98a4a21..b434cfbbb0e 100644
--- a/source/blender/gpu/intern/gpu_shader.cc
+++ b/source/blender/gpu/intern/gpu_shader.cc
@@ -88,6 +88,16 @@ static void standard_defines(Vector<const char *> &sources)
   else if (GPU_type_matches(GPU_DEVICE_ANY, GPU_OS_UNIX, GPU_DRIVER_ANY)) {
     sources.append("#define OS_UNIX\n");
   }
+  /* API Definition */
+  eGPUBackendType backend = GPU_backend_get_type();
+  switch (backend) {
+    case GPU_BACKEND_OPENGL:
+      sources.append("#define GPU_OPENGL\n");
+      break;
+    default:
+      BLI_assert(false && "Invalid GPU Backend Type");
+      break;
+  }
 
   if (GPU_crappy_amd_driver()) {
     sources.append("#define GPU_DEPRECATED_AMD_DRIVER\n");
diff --git a/source/blender/gpu/opengl/gl_shader.cc b/source/blender/gpu/opengl/gl_shader.cc
index c0182306047..c76e21f9f71 100644
--- a/source/blender/gpu/opengl/gl_shader.cc
+++ b/source/blender/gpu/opengl/gl_shader.cc
@@ -24,6 +24,8 @@ using namespace blender;
 using namespace blender::gpu;
 using namespace blender::gpu::shader;
 
+extern char datatoc_glsl_shader_defines_glsl[];
+
 /* -------------------------------------------------------------------- */
 /** \name Creation / Destruction
  * \{ */
@@ -760,7 +762,7 @@ bool GLShader::do_geometry_shader_injection(const shader::ShaderCreateInfo *info
 static char *glsl_patch_default_get()
 {
   /** Used for shader patching. Init once. */
-  static char patch[1024] = "\0";
+  static char patch[2048] = "\0";
   if (patch[0] != '\0') {
     return patch;
   }
@@ -827,6 +829,9 @@ static char *glsl_patch_default_get()
   STR_CONCATF(patch, slen, "#define DFDX_SIGN %1.1f\n", GLContext::derivative_signs[0]);
   STR_CONCATF(patch, slen, "#define DFDY_SIGN %1.1f\n", GLContext::derivative_signs[1]);
 
+  /* GLSL Backend Lib. */
+  STR_CONCAT(patch, slen, datatoc_glsl_shader_defines_glsl);
+
   BLI_assert(slen < sizeof(patch));
   return patch;
 }
diff --git a/source/blender/gpu/shaders/gpu_shader_2D_image_multi_rect_vert.glsl b/source/blender/gpu/shaders/gpu_shader_2D_image_multi_rect_vert.glsl
index 9851e08fe2e..353bf1481da 100644
--- a/source/blender/gpu/shaders/gpu_shader_2D_image_multi_rect_vert.glsl
+++ b/source/blender/gpu/shaders/gpu_shader_2D_image_multi_rect_vert.glsl
@@ -23,15 +23,15 @@ void main()
 
   /* Use pos to select the right swizzle (instead of gl_VertexID)
    * in order to workaround an OSX driver bug. */
-  if (pos == vec2(0.0, 0.0)) {
+  if (all(equal(pos, vec2(0.0, 0.0)))) {
     rect.xy = rect.xz;
     tex.xy = tex.xz;
   }
-  else if (pos == vec2(0.0, 1.0)) {
+  else if (all(equal(pos, vec2(0.0, 1.0)))) {
     rect.xy = rect.xw;
     tex.xy = tex.xw;
   }
-  else if (pos == vec2(1.0, 1.0)) {
+  else if (all(equal(pos, vec2(1.0, 1.0)))) {
     rect.xy = rect.yw;
     tex.xy = tex.yw;
   }
diff --git a/source/blender/gpu/shaders/gpu_shader_2D_image_rect_vert.glsl b/source/blender/gpu/shaders/gpu_shader_2D_image_rect_vert.glsl
index d9a5aeeef46..903c602c5d6 100644
--- a/source/blender/gpu/shaders/gpu_shader_2D_image_rect_vert.glsl
+++ b/source/blender/gpu/shaders/gpu_shader_2D_image_rect_vert.glsl
@@ -15,6 +15,32 @@ void main()
 {
   vec2 uv;
   vec2 co;
+
+#ifdef GPU_METAL
+/* Metal API does not support Triangle fan primitive topology.
+ * When this shader is called using Triangle-Strip, vertex ID's
+ * are in a different order. */
+#  define GPU_PRIM_TRI_STRIP
+#endif
+
+#ifdef GPU_PRIM_TRI_STRIP
+  if (gl_VertexID == 0) {
+    co = rect_geom.xw;
+    uv = rect_icon.xw;
+  }
+  else if (gl_VertexID == 1) {
+    co = rect_geom.xy;
+    uv = rect_icon.xy;
+  }
+  else if (gl_VertexID == 2) {
+    co = rect_geom.zw;
+    uv = rect_icon.zw;
+  }
+  else {
+    co = rect_geom.zy;
+    uv = rect_icon.zy;
+  }
+#else
   if (gl_VertexID == 0) {
     co = rect_geom.xy;
     uv = rect_icon.xy;
@@ -31,6 +57,7 @@ void main()
     co = rect_geom.zy;
     uv = rect_icon.zy;
   }
+#endif
 
   gl_Position = ModelViewProjectionMatrix * vec4(co, 0.0f, 1.0f);
   texCoord_interp = uv;
diff --git a/source/blender/gpu/shaders/gpu_shader_2D_widget_base_vert.glsl b/source/blender/gpu/shaders/gpu_shader_2D_widget_base_vert.glsl
index 80b93baf20a..3a39cd8b847 100644
--- a/source/blender/gpu/shaders/gpu_shader_2D_widget_base_vert.glsl
+++ b/source/blender/gpu/shaders/gpu_shader_2D_widget_base_vert.glsl
@@ -53,7 +53,7 @@ flat out float lineWidth;
 noperspective out float butCo;
 flat out float discardFac;
 
-#  ifdef OS_MAC
+#  if defined(OS_MAC) && defined(GPU_OPENGL)
 in float dummy;
 #  endif
 #endif
diff --git a/source/blender/gpu/shaders/gpu_shader_image_overlays_merge_frag.glsl b/source/blender/gpu/shaders/gpu_shader_image_overlays_merge_frag.glsl
index 2314dbbc5d5..aa182eb52be 100644
--- a/source/blender/gpu/shaders/gpu_shader_image_overlays_merge_frag.glsl
+++ b/source/blender/gpu/shaders/gpu_shader_image_overlays_merge_frag.glsl
@@ -32,9 +32,9 @@ void linearrgb_to_srgb(vec4 col_from, out vec4 col_to)
 
 void main()
 {
-  fragColor = texture(image_texture, texCoord_interp.st);
-  vec4 overlay_col = texture(overlays_texture, texCoord_interp.st);
-
+  fragColor = texture(image_texture, texCoord_interp.xy);
+  vec4 overlay_col = texture(overlays_texture, texCoord_interp.xy);
+  
   if (overlay) {
     fragColor = clamp(fragColor, 0.0, 1.0);
     fragColor *= 1.0 - overlay_col.a;
diff --git a/source/blender/gpu/shaders/gpu_shader_keyframe_shape_vert.glsl b/source/blender/gpu/shaders/gpu_shader_keyframe_shape_vert.glsl
index 4ef3ff1a8d0..617c02ac079 100644
--- a/source/blender/gpu/shaders/gpu_shader_keyframe_shape_vert.glsl
+++ b/source/blender/gpu/shaders/gpu_shader_keyframe_shape_vert.glsl
@@ -43,7 +43,7 @@ bool test(int bit)
 
 vec2 line_thresholds(float width)
 {
-  return vec2(max(0, width - line_falloff), width);
+  return vec2(max(0.0, width - line_falloff), width);
 }
 
 void main()
diff --git a/source/blender/gpu/shaders/gpu_shader_text_frag.glsl b/source/blender/gpu/shaders/gpu_shader_text_frag.glsl
index c339d3cbabb..f958a81b1eb 100644
--- a/source/blender/gpu/shaders/gpu_shader_text_frag.glsl
+++ b/source/blender/gpu/shaders/gpu_shader_text_frag.glsl
@@ -52,7 +52,7 @@ bool is_inside_box(ivec2 v)
 
 float texture_1D_custom_bilinear_filter(vec2 uv)
 {
-  vec2 texel_2d = uv * glyph_dim + 0.5;
+  vec2 texel_2d = uv * vec2(glyph_dim) + vec2(0.5);
   ivec2 texel_2d_near = ivec2(texel_2d) - 1;
   int frag_offset = glyph_offset + texel_2d_near.y * glyph_dim.x + texel_2d_near.x;
 
@@ -100,7 +100,7 @@ void main()
     fragColor.a = texture_1D_custom_bilinear_filter(texCoord_interp);
   }
   else {
-    vec2 texel = 1.0 / glyph_dim;
+    vec2 texel = 1.0 / vec2(glyph_dim);
     fragColor.a = 0.0;
 
     if (interp_size == 1) {
diff --git a/source/blender/gpu/shaders/gpu_shader_text_vert.glsl b/source/blender/gpu/shaders/gpu_shader_text_vert.glsl
index 5b01fea5266..4221e426a3e 100644
--- a/source/blender/gpu/shaders/gpu_shader_text_vert.glsl
+++ b/source/blender/gpu/shaders/gpu_shader_text_vert.glsl
@@ -29,7 +29,7 @@ void main()
   texCoord_interp = mix(-interp_offset, 1.0 + interp_offset, quad);
 
   vec2 final_pos = mix(
-      pos.xy + ivec2(-interp_size, interp_size), pos.zw + ivec2(interp_size, -interp_size), quad);
+      vec2(ivec2(pos.xy) + ivec2(-interp_size, interp_size)), vec2(ivec2(pos.zw) + ivec2(interp_size, -interp_size)), quad);
 
   gl_Position = ModelViewProjectionMatrix * vec4(final_pos, 0.0, 1.0);
 }
diff --git a/source/blender/gpu/shaders/material/gpu_shader_material_light_falloff.glsl b/source/blender/gpu/shaders/material/gpu_shader_material_light_falloff.glsl
index f3eae653f95..e1c7a00646f 100644
--- a/source/blender/gpu/shaders/material/gpu_shader_material_light_falloff.glsl
+++ b/source/blender/gpu/shaders/material/gpu_shader_material_light_falloff.glsl
@@ -1,7 +1,7 @@
 void node_light_falloff(
-    float strength, float tsmooth, out float quadratic, out float linear, out float constant)
+    float strength, float tsmooth, out float quadratic, out float linear, out float falloff_constant)
 {
   quadratic = strength;
   linear = strength;
-  constant = strength;
+  falloff_constant = strength;
 }
diff --git a/source/blender/gpu/shaders/opengl/glsl_shader_defines.glsl b/source/blender/gpu/shaders/opengl/glsl_shader_defines.glsl
new file mode 100644
index 00000000000..a5fce2e71c3
--- /dev/null
+++ b/source/blender/gpu/shaders/opengl/glsl_shader_defines.glsl
@@ -0,0 +1,17 @@
+/* Backend Functions. */
+#define select(A, B, mask) mix(A, B, mask)
+
+bool is_zero(vec2 A)
+{
+  return all(equal(A, vec2(0.0)));
+}
+
+bool is_zero(vec3 A)
+{
+  return all(equal(A, vec3(0.0)));
+}
+
+bool is_zero(vec4 A)
+{
+  return all(equal(A, vec4(0.0)));
+}