ff-render 0.14.2

GPU compositing pipeline for real-time preview (wgpu-based)
Documentation 
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// Shared mask shader: ShapeMask (mode=0), LumaMask (mode=1), AlphaMatte (mode=2).
struct VertexOutput {
    @builtin(position) position: vec4<f32>,
    @location(0) uv: vec2<f32>,
}

@vertex
fn vs_main(@builtin(vertex_index) vertex_idx: u32) -> VertexOutput {
    var positions = array<vec2<f32>, 6>(
        vec2<f32>(-1.0,  1.0), vec2<f32>( 1.0,  1.0), vec2<f32>(-1.0, -1.0),
        vec2<f32>(-1.0, -1.0), vec2<f32>( 1.0,  1.0), vec2<f32>( 1.0, -1.0),
    );
    var uvs = array<vec2<f32>, 6>(
        vec2<f32>(0.0, 0.0), vec2<f32>(1.0, 0.0), vec2<f32>(0.0, 1.0),
        vec2<f32>(0.0, 1.0), vec2<f32>(1.0, 0.0), vec2<f32>(1.0, 1.0),
    );
    var out: VertexOutput;
    out.position = vec4<f32>(positions[vertex_idx], 0.0, 1.0);
    out.uv = uvs[vertex_idx];
    return out;
}

// ── Bindings ──────────────────────────────────────────────────────────────────

@group(0) @binding(0) var tex_base:    texture_2d<f32>;  // base / foreground
@group(0) @binding(1) var tex_mask:    texture_2d<f32>;  // mask / background
@group(0) @binding(2) var tex_sampler: sampler;
@group(0) @binding(3) var<uniform> u: MaskUniforms;

struct MaskUniforms {
    // 0 = ShapeMask, 1 = LumaMask, 2 = AlphaMatte
    mode: u32,
    _pad0: u32,
    _pad1: u32,
    _pad2: u32,
}

// ── Fragment ──────────────────────────────────────────────────────────────────

@fragment
fn fs_main(in: VertexOutput) -> @location(0) vec4<f32> {
    let base = textureSample(tex_base, tex_sampler, in.uv);
    let mask = textureSample(tex_mask, tex_sampler, in.uv);

    var out: vec4<f32>;
    switch u.mode {
        // ShapeMask: apply mask's alpha as a hard threshold.
        case 0u {
            let alpha = select(0.0, 1.0, mask.a > 0.004);
            out = vec4<f32>(base.rgb, base.a * alpha);
        }
        // LumaMask: use mask's BT.709 luma as opacity.
        case 1u {
            let luma = dot(mask.rgb, vec3<f32>(0.2126, 0.7152, 0.0722));
            out = vec4<f32>(base.rgb, base.a * luma);
        }
        // AlphaMatte: Porter-Duff src-over (base = foreground, mask = background).
        case 2u {
            let alpha   = base.a;
            let out_rgb = base.rgb * alpha + mask.rgb * (1.0 - alpha);
            let out_a   = alpha + mask.a * (1.0 - alpha);
            out = vec4<f32>(out_rgb, out_a);
        }
        default {
            out = base;
        }
    }
    return out;
}