sugarloaf 0.4.4

Sugarloaf is Rio rendering engine, designed to be multiplatform. It is based on WebGPU, Rust library for Desktops and WebAssembly for Web (JavaScript). This project is created and maintained for Rio terminal purposes but feel free to use it.
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#version 450

// Text fragment shader. Two atlases bound — grayscale (R8) for outline
// glyphs, RGBA8 for color emoji. The vertex shader's `out_atlas` flag
// picks which one to read.
//
// Sampling is `texelFetch` (nearest, no filtering) at integer pixel
// coordinates — matches Metal's `coord::pixel` + `filter::nearest`.

layout(set = 1, binding = 0) uniform sampler2D atlas_grayscale;
layout(set = 1, binding = 1) uniform sampler2D atlas_color;

layout(location = 0) flat in uint in_atlas;
layout(location = 1) flat in vec4 in_color;
layout(location = 2)      in vec2 in_tex_coord;

layout(location = 0) out vec4 out_color;

const uint ATLAS_GRAYSCALE = 0u;

void main() {
    ivec2 uv = ivec2(in_tex_coord);
    if (in_atlas == ATLAS_GRAYSCALE) {
        // Grayscale: sample alpha mask, multiply by per-glyph color.
        // Colour is already premultiplied (in_color.rgb *= in_color.a
        // in the vertex shader), so the result is also premultiplied.
        float a = texelFetch(atlas_grayscale, uv, 0).r;
        out_color = in_color * a;
    } else {
        // Color atlas: sample RGBA premultiplied directly.
        out_color = texelFetch(atlas_color, uv, 0);
    }
}