#version 330 core
out vec4 FragColor;
in vec2 TexCoord;

uniform sampler2D inputImageTexture;
uniform sampler2D inputImageTexture2;
uniform float mixturePercent;
uniform int   directionType;

// Both clips translate together: outgoing slides off-screen toward the named
// edge, incoming slides in from the opposite edge. directionType convention
// same as transition_slide.fs.
void main() {
    if (directionType == 2) {
        if (TexCoord.y > mixturePercent) {
            FragColor = texture(inputImageTexture,
                                vec2(TexCoord.x, TexCoord.y - mixturePercent));
        } else {
            FragColor = texture(inputImageTexture2,
                                vec2(TexCoord.x, TexCoord.y + (1.0 - mixturePercent)));
        }
    } else if (directionType == 1) {
        if (TexCoord.x > mixturePercent) {
            FragColor = texture(inputImageTexture,
                                vec2(TexCoord.x - mixturePercent, TexCoord.y));
        } else {
            FragColor = texture(inputImageTexture2,
                                vec2(TexCoord.x + (1.0 - mixturePercent), TexCoord.y));
        }
    } else if (directionType == 0) {
        float p = 1.0 - mixturePercent;
        if (TexCoord.y < p) {
            FragColor = texture(inputImageTexture,
                                vec2(TexCoord.x, TexCoord.y + (1.0 - p)));
        } else {
            FragColor = texture(inputImageTexture2,
                                vec2(TexCoord.x, TexCoord.y - p));
        }
    } else if (directionType == 3) {
        float p = 1.0 - mixturePercent;
        if (TexCoord.x < p) {
            FragColor = texture(inputImageTexture,
                                vec2(TexCoord.x + (1.0 - p), TexCoord.y));
        } else {
            FragColor = texture(inputImageTexture2,
                                vec2(TexCoord.x - p, TexCoord.y));
        }
    } else {
        vec4 a = texture(inputImageTexture,  TexCoord);
        vec4 b = texture(inputImageTexture2, TexCoord);
        FragColor = mix(a, b, mixturePercent);
    }
}