precision highp float;

varying vec2 textureCoordinate;
uniform sampler2D from;
uniform sampler2D to;
uniform float progress;

vec4 getFromColor(vec2 uv) {
    return texture2D(from,uv);
}

vec4 getToColor(vec2 uv){
    return texture2D(to,uv);
}

#define PI 3.14159265358979323
#define POW2(X) X*X
#define POW3(X) X*X*X
int endx = 2;
int endy = -1;

float Rand(vec2 v) {
    return fract(sin(dot(v.xy ,vec2(12.9898,78.233))) * 43758.5453);
}
vec2 Rotate(vec2 v, float a) {
    mat2 rm = mat2(cos(a), -sin(a),
                   sin(a), cos(a));
    return rm*v;
}
float CosInterpolation(float x) {
    return -cos(x*PI)/2.+.5;
}
vec4 transition(vec2 uv) {
    vec2 p = uv.xy / vec2(1.0).xy - .5;
    vec2 rp = p;
    float rpr = (progress*2.-1.);
    float z = -(rpr*rpr*2.) + 3.;
    float az = abs(z);
    rp *= az;
    rp += mix(vec2(.5, .5), vec2(float(endx) + .5, float(endy) + .5), POW2(CosInterpolation(progress)));
    vec2 mrp = mod(rp, 1.);
    vec2 crp = rp;
    bool onEnd = int(floor(crp.x))==endx&&int(floor(crp.y))==endy;
    if(!onEnd) {
        float ang = float(int(Rand(floor(crp))*4.))*.5*PI;
        mrp = vec2(.5) + Rotate(mrp-vec2(.5), ang);
    }
    if(onEnd || Rand(floor(crp))>.5) {
        return getToColor(mrp);
    } else {
        return getFromColor(mrp);
    }
}
void main(){
    gl_FragColor = transition(textureCoordinate);
    }