petertretyakov · August 4, 2022 15:59 · Aug 4, 2022
diff --git a/gradient.metal b/gradient.metal
@@ -0,0 +1,86 @@
+// Gradient Shader for arbitrary gradient stops, three gradient types and rotation
+// For the details please visit: https://mtldoc.com/metal/2022/08/04/shaders-explained-gradients.html
+
+// MARK: - Gradient Texture
+
+struct GradientTextureVertex {
+    float4 position [[ position ]];
+    float4 color;
+};
+
+[[ vertex ]]
+GradientTextureVertex gradientTextureVertex(constant float* positions [[ buffer(0) ]],
+                                            constant float4* colors [[ buffer(1) ]],
+                                            const ushort vid [[ vertex_id ]]) {
+    return {
+        .position = float4(fma(positions[vid], 2.0f, -1.0f), 0.0f, 0.0f, 1.0f),
+        .color = colors[vid]
+    };
+}
+
+[[ fragment ]]
+float4 gradientTextureFragment(GradientTextureVertex in [[ stage_in ]]) {
+    return in.color;
+}
+
+// MARK: - Gradient
+
+enum GradientType: uchar {
+    kLinear,
+    kRadial,
+    kAngular
+};
+
+struct GradientVertex {
+    float4 position [[ position ]];
+    float2 uv;
+};
+
+constant float2 positions[4] {
+    { -1.0f,  1.0f },
+    { -1.0f, -1.0f },
+    {  1.0f,  1.0f },
+    {  1.0f, -1.0f }
+};
+
+constant float2 uvs[4] {
+    { 0.0f, 0.0f },
+    { 0.0f, 1.0f },
+    { 1.0f, 0.0f },
+    { 1.0f, 1.0f }
+};
+
+constant float PI = 3.1415926f;
+
+[[ vertex ]]
+GradientVertex gradientVertex(constant float2x2& rotationTransform [[ buffer(0) ]],
+                              const ushort vid [[ vertex_id ]]) {
+    return {
+        .position = float4(positions[vid], 0.0f, 1.0f),
+        .uv = (uvs[vid] - float2(0.5f)) * rotationTransform + float2(0.5f)
+    };
+}
+
+[[ fragment ]]
+float4 gradientFragment(GradientVertex in [[ stage_in ]],
+                        texture2d<float, access::sample> gradientTexture [[ texture(0) ]],
+                        constant GradientType& gradientType [[ buffer(0) ]]) {
+    constexpr sampler s(filter::linear, coord::normalized, address::clamp_to_edge);
+
+    float2 texCoords;
+    switch (gradientType) {
+        case kLinear:
+            texCoords = in.uv;
+            break;
+        case kRadial:
+            texCoords = length(in.uv - float2(0.5f)) * 2.0f;
+            break;
+        case kAngular:
+            const float2 offsetUV = in.uv - float2(0.5f);
+            const float angle = atan2(offsetUV.y, offsetUV.x);
+            texCoords = float2(fma(angle / PI, 0.5f, 0.5f), 0.0f);
+            break;
+    }
+
+    return gradientTexture.sample(s, texCoords);
+}