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Forked from petertretyakov/gradient.metal
Created August 6, 2022 07:53
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// 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);
}
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