#version 330 core

// Interpolated values from the vertex shaders
in vec2 UV;

// Ouput data
out vec3 color;

// Values that stay constant for the whole mesh.
uniform sampler2D trimap;
uniform sampler2D foreground;
uniform sampler2D background;

// Relative width/height of a pixel
uniform float pixWidth;
uniform float pixHeight;

int IS_BACKGROUND = 0;
int IS_UNDEFINED = 1;
int IS_FOREGROUND = 2;
int UNSET = -1;

vec3 getTriColor(vec2 uvCoord) {
    return texture(trimap, uvCoord).rgb;
}

vec3 getForeColor(vec2 uvCoord) {
    return texture(foreground, uvCoord).rgb;
}

vec3 getBackColor(vec2 uvCoord) {
    return texture(background, uvCoord).rgb;
}

int getState(vec3 c) {
    if (all(lessThanEqual(c, vec3(0.2f)))) {
        return IS_BACKGROUND;
    } else if (all(greaterThanEqual(c, vec3(0.8f)))) {
        return IS_FOREGROUND;
    } else {
        return IS_UNDEFINED;
    }
}


void main(){
    color = getTriColor(UV);
    int status = getState(color);


    if (status==IS_FOREGROUND) {
        color = getForeColor(UV).rgb;
    } else if (status==IS_BACKGROUND) {
        color = getBackColor(UV).rgb;
    } else {
        // render undefined area
    }
}