rustial-renderer-wgpu 1.0.0

// Heatmap accumulation shader.
//
// Pass 1: Accumulates Gaussian weight contributions into an R16Float
//          framebuffer using additive blending.
// The colour mapping pass uses the grid_scalar pipeline with a ramp texture.

struct Uniforms {
    view_proj:  mat4x4<f32>,
    fog_color:  vec4<f32>,
    eye_pos:    vec4<f32>,
    fog_params: vec4<f32>,
};

struct HeatmapVertexInput {
    @location(0) position:    vec3<f32>,
    @location(1) quad_offset: vec2<f32>,
    @location(2) params:      vec4<f32>,   // (weight, radius, intensity, 0)
};

struct HeatmapVertexOutput {
    @builtin(position) clip_position: vec4<f32>,
    @location(0) quad_uv:   vec2<f32>,
    @location(1) params:    vec4<f32>,
};

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

@vertex
fn vs_main(in: HeatmapVertexInput) -> HeatmapVertexOutput {
    let radius = in.params.y;

    // Expand quad around centre.
    let expanded = in.position + vec3<f32>(
        in.quad_offset.x * radius,
        in.quad_offset.y * radius,
        0.0,
    );

    var out: HeatmapVertexOutput;
    out.clip_position = u.view_proj * vec4<f32>(expanded, 1.0);
    out.quad_uv = in.quad_offset;
    out.params = in.params;
    return out;
}

@fragment
fn fs_main(in: HeatmapVertexOutput) -> @location(0) vec4<f32> {
    let weight    = in.params.x;
    let intensity = in.params.z;

    // Gaussian kernel: exp(-d^2 / (2 * sigma^2)) where sigma = 1/3
    // so that the kernel reaches ~zero at the quad edge (|uv| = 1).
    let dist_sq = dot(in.quad_uv, in.quad_uv);
    if dist_sq > 1.0 {
        discard;
    }
    let sigma = 1.0 / 3.0;
    let gauss = exp(-dist_sq / (2.0 * sigma * sigma));
    let value = gauss * weight * intensity;

    // Output accumulated weight into a single-channel framebuffer.
    return vec4<f32>(value, 0.0, 0.0, 1.0);
}