#version 330

uniform sampler2D cloudTexture;
uniform sampler2D perlinNoise;

uniform vec4 cloudColour1;
uniform vec4 cloudColour2;
uniform vec4 cloudColour3;
uniform vec4 cloudColour4;

// Must match the names in compoundClouds.vs
in vec2 oUV0;

out vec4 color;

void main()
{
    vec4 concentrations = texture2D(cloudTexture, oUV0);

    // Calculate all channels
    float alpha1 = concentrations.r * texture2D(perlinNoise, oUV0 * 1.5f + 0.0f).x * 0.90f;
    float alpha2 = concentrations.g * texture2D(perlinNoise, oUV0 * 1.5f + 0.2f).x * 0.90f;
    float alpha3 = concentrations.b * texture2D(perlinNoise, oUV0 * 1.5f + 0.04f).x * 0.90f;
    float alpha4 = concentrations.a * texture2D(perlinNoise, oUV0 * 1.5f + 0.6f).x * 0.90f;

    float totalAlpha = alpha1 + alpha2 + alpha3 + alpha4;

    // Adjust the alpha to get better looking blend
    alpha1 *= alpha1 / totalAlpha;
    alpha2 *= alpha2 / totalAlpha;
    alpha3 *= alpha3 / totalAlpha;
    alpha4 *= alpha4 / totalAlpha;

    // Then mix them all together
    color =
        // first
        cloudColour1 * alpha1 +
        // second
        cloudColour2 * alpha2 +
        // third
        cloudColour3 * alpha3 +
        // fourth
        cloudColour4 * alpha4;
}