facett-core 0.1.7

facett — visual kernel: render a node/edge Scene into egui (wgpu fast path to come)
Documentation 
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// Line-draw shader for OSM ways.
// Vertices are in Mercator [0,1] space with pre-baked RGBA color.
// Uniforms carry zoom, pan offset, and viewport size so the VS can
// map directly to clip space without knowing the logical resolution at
// compile time.

struct Uniforms {
    zoom:       f32,
    offset_x:   f32,
    offset_y:   f32,
    _pad:       f32,
    viewport_w: f32,
    viewport_h: f32,
    _pad2:      vec2<f32>,
}

@group(0) @binding(0) var<uniform> u: Uniforms;

struct VertexOut {
    @builtin(position) pos: vec4<f32>,
    @location(0)       col: vec4<f32>,
}

@vertex
fn vs_main(
    @location(0) mercator: vec2<f32>,
    @location(1) color:    vec4<f32>,
) -> VertexOut {
    // Mercator [0,1] → screen pixel (logical)
    let sx = mercator.x * u.zoom + u.offset_x;
    let sy = mercator.y * u.zoom + u.offset_y;
    // Screen pixel → clip space [-1, 1]; y is flipped (screen y=0 is top)
    let cx = sx / (u.viewport_w * 0.5) - 1.0;
    let cy = 1.0 - sy / (u.viewport_h * 0.5);
    return VertexOut(vec4<f32>(cx, cy, 0.0, 1.0), color);
}

@fragment
fn fs_main(in: VertexOut) -> @location(0) vec4<f32> {
    return in.col;
}