teksilo-render 0.17.1

wgpu renderer for Teksilo — rect, SDF and path pipelines with a glyph atlas.
Documentation 
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// SPDX-License-Identifier: MPL-2.0
// SPDX-FileCopyrightText: 2026 FernTech

// Dual-Kawase blur — downsample pass.
//
// Samples the input texture at four diagonal offsets around each
// destination texel and averages them. Combined with the matching
// upsample shader, this approximates a Gaussian blur at much lower
// cost than a separable Gaussian for radii ≳ 8 px.
//
// The vertex shader is the full-screen triangle of `fullscreen.wgsl`,
// which is prepended to this file.

struct VertexOutput {
    @builtin(position) clip_position: vec4<f32>,
    @location(0) uv: vec2<f32>,
};

struct Params {
    // Texel size of the SOURCE texture in 0..1 UV units, scaled by the
    // sample-offset parameter. Pre-baked CPU-side so the shader stays
    // branch-free. `.zw` is unused (std140 alignment padding).
    offset: vec4<f32>,
};

@group(0) @binding(0) var source_texture: texture_2d<f32>;
@group(0) @binding(1) var source_sampler: sampler;
@group(0) @binding(2) var<uniform> params: Params;

@vertex
fn vs_main(@builtin(vertex_index) idx: u32) -> VertexOutput {
    let p = fullscreen_position(idx);
    var out: VertexOutput;
    out.clip_position = p;
    // Map clip XY (-1..1) → UV (0..1), flipping Y so origin is top-left
    // (matches the way the rest of the renderer hands UVs to textures).
    out.uv = vec2<f32>(p.x * 0.5 + 0.5, 1.0 - (p.y * 0.5 + 0.5));
    return out;
}

@fragment
fn fs_main(in: VertexOutput) -> @location(0) vec4<f32> {
    let off = params.offset.xy;
    // Center sample weighted by 4, plus four corner samples each
    // weighted by 1, normalized by 8 — same kernel weights Marius
    // Bjørge published in the Siggraph 2015 dual-Kawase paper.
    let center = textureSample(source_texture, source_sampler, in.uv) * 4.0;
    let c1 = textureSample(source_texture, source_sampler, in.uv + vec2<f32>(-off.x, -off.y));
    let c2 = textureSample(source_texture, source_sampler, in.uv + vec2<f32>( off.x, -off.y));
    let c3 = textureSample(source_texture, source_sampler, in.uv + vec2<f32>(-off.x,  off.y));
    let c4 = textureSample(source_texture, source_sampler, in.uv + vec2<f32>( off.x,  off.y));
    return (center + c1 + c2 + c3 + c4) / 8.0;
}