#version 450

layout(set = 2, binding = 0) uniform sampler2D u_image;
layout(std140, set = 3, binding = 0) uniform UiUniforms {
    float background_opacity;
} u_ui;

layout(location = 0) in vec2 v_uv;
layout(location = 1) in vec2 v_panel_uv;
layout(location = 2) flat in uvec4 v_effect;
layout(location = 0) out vec4 o_col;

float cellNoise(uint serial, uint col, uint row) {
    uint x = serial ^ (col * 0x9e3779b9u) ^ (row * 0x85ebca6bu);
    x ^= x >> 16;
    x *= 0x7feb352du;
    x ^= x >> 15;
    x *= 0x846ca68bu;
    x ^= x >> 16;
    return float(x & 0xffffu) / 65535.0;
}

void main() {
    vec4 source = texture(u_image, v_uv);
    // Keep source coverage for destination subtraction; the pipeline scales
    // source alpha by the same opacity through its alpha blend constant.
    source.rgb *= clamp(u_ui.background_opacity, 0.0, 1.0);
    uint effect = v_effect.x & 0x7fffffffu;
    bool oldLayer = (v_effect.x & 0x80000000u) != 0u;
    float progress = clamp(uintBitsToFloat(v_effect.y), 0.0, 1.0);
    uvec2 dimensions = max(
        uvec2(v_effect.w & 0xffffu, v_effect.w >> 16),
        uvec2(1u));
    uvec2 cellCoord = min(
        uvec2(floor(max(v_panel_uv, vec2(0.0)) * vec2(dimensions))),
        dimensions - 1u);
    float noise = cellNoise(v_effect.z, cellCoord.x, cellCoord.y);
    if (effect == 3u) {
        bool reveal = progress >= 1.0 || (progress > 0.0 && noise < progress);
        if (oldLayer == reveal) discard;
        o_col = source;
        return;
    }
    o_col = source;
}