#version 450
#extension GL_ARB_separate_shader_objects : enable

layout(location = 0) in vec2 fUv;
layout(location = 1) in flat uint fChannels;

layout(location = 0) out vec4 result;

layout(binding = 1) uniform Opt
{
    vec4 multiplier;
    bool preMultiply;
} opt;

layout(binding = 2) uniform sampler2D render;

void main()
{
    result = opt.multiplier;
    if (fChannels == 1)
        result *= vec4(texture(render, fUv).rrr, 1.0f);
    else if (fChannels == 2)
        result *= vec4(texture(render, fUv).rrr, texture(render, fUv).g);
    else if (fChannels == 3)
        result *= vec4(texture(render, fUv).rgb, 1.0f);
    else if (fChannels == 4)
        result *= texture(render, fUv).rgba;

    if (opt.preMultiply)
        result = vec4(result.rgb * result.a, result.a);
}