65 lines
2.1 KiB
Plaintext
65 lines
2.1 KiB
Plaintext
#include <metal_stdlib>
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using namespace metal;
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struct VertexOut {
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float4 position [[position]];
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float2 uv;
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float4 color;
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};
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struct Uniforms {
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float outline_width; // Outline width in normalized SDF units (0.0 = no outline, 0.1-0.3 typical)
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float sharpness; // Sharpness multiplier (1.0 = normal, higher = sharper)
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float2 _pad; // Padding for alignment
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float4 outline_color; // Outline color RGBA
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};
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// Median of three values - used to combine MSDF channels
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float median(float r, float g, float b) {
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return max(min(r, g), min(max(r, g), b));
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}
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fragment float4 fragment_main(VertexOut in [[stage_in]],
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texture2d<float> tex [[texture(0)]],
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sampler smp [[sampler(0)]],
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constant Uniforms &u [[buffer(0)]]) {
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// Sample RGB channels from MSDF texture
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float3 msdf = tex.sample(smp, in.uv).rgb;
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// Compute signed distance from the median of the three channels
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float dist = median(msdf.r, msdf.g, msdf.b);
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// Edge is at 0.5 (where distance = 0 in the original SDF)
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float edge = 0.5;
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// Calculate anti-aliasing width based on screen-space derivatives
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// MSDF typically needs tighter AA than single-channel SDF
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float aa = fwidth(dist);
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float sharpness = max(u.sharpness, 0.1);
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aa = aa / sharpness;
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// Fill coverage: inside the glyph
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float fill = smoothstep(edge - aa, edge + aa, dist);
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// Outline coverage: extends outward from the edge
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float outline_coverage = 0.0;
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if (u.outline_width > 0.0) {
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float outline_edge = edge - u.outline_width;
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outline_coverage = smoothstep(outline_edge - aa, outline_edge + aa, dist);
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}
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// Total coverage is the union of fill and outline
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float total_coverage = max(fill, outline_coverage);
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// Blend colors: outline where not filled, fill color where filled
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float3 rgb = in.color.rgb;
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if (u.outline_width > 0.0) {
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rgb = mix(u.outline_color.rgb, in.color.rgb, fill);
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}
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// Final alpha combines coverage with vertex alpha
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float a = total_coverage * in.color.a;
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return float4(rgb, a);
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}
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