import { ShaderProgram } from "../webgl/ShaderProgram";

export function weightedOITResolve() {
    return new ShaderProgram("weightedOITResolve", {
        uniforms: {
            uAccumulate: "sampler2D",
            uAccumulateAlpha: "sampler2D"
        },
        attributes: {
            corners: "vec2"
        },
        vertexShader: `#version 300 es
            in vec2 corners;

            void main() {
                gl_Position = vec4(corners, 0.0, 1.0);
            }`,
        fragmentShader: `#version 300 es
            precision highp float;

            uniform sampler2D uAccumulate;
            uniform sampler2D uAccumulateAlpha;

            out vec4 fragColor;

            const float EPS = 0.00001;

            void main() {
                ivec2 fragCoord = ivec2(gl_FragCoord.xy);
                vec4 accum = texelFetch(uAccumulate, fragCoord, 0);

                float revealage = accum.a;

                if (revealage >= 0.9999) {
                    discard;
                }

                float accumAlpha = texelFetch(uAccumulateAlpha, fragCoord, 0).r;

                // prevent floating point precision bug
                vec3 averageColor = accum.rgb / max(accumAlpha, EPS);

                float a = 1.0 - revealage;
                fragColor = vec4(averageColor * a, a);
            }`
    });
}