#ifdef GL_ES
precision mediump float;
precision mediump int;
#endif

uniform sampler2D u_texture;

uniform vec4 u_color;
uniform vec2 u_texsize;
uniform vec2 u_uv;
uniform vec2 u_uv2;
uniform float u_progress;
uniform float u_time;

varying vec4 v_color;
varying vec2 v_texCoord;

float diff(vec4 target, vec4 base){
    return (max(target.a / base.a, max(target.r / base.r, max(target.g / base.g, target.b / base.b))) -
               min (target.a / base.a, min(target.r / base.r, min(target.g / base.g, target.b / base.b)))) * 4.0;
}

bool id(vec2 coords, vec4 base, float basediff){
    vec4 target = texture2D(u_texture, coords);
    return (diff(target, base)) > basediff - basediff*u_progress
        || (basediff < 5.0 && (coords.x < u_uv.x || coords.y < u_uv.y || coords.x > u_uv2.x || coords.y > u_uv2.y));
}

bool cont(vec2 T, vec2 v, float basediff){
    float step = 1.0;
    vec4 base = texture2D(u_texture, T);
    return base.a > 0.1 &&
           		(id(T + vec2(0, step) * v, base, basediff) || id(T + vec2(0, -step) * v, base, basediff) ||
           		id(T + vec2(step, 0) * v, base, basediff) || id(T + vec2(-step, 0) * v, base, basediff));
}

float rand(vec2 co){
    return fract(sin(dot(co.xy ,vec2(12.9898,78.233))) * 43758.5453);
}

void main() {

	vec2 t = v_texCoord.xy;

	vec2 v = vec2(1.0/u_texsize.x, 1.0/u_texsize.y);
	vec2 coords = (v_texCoord-u_uv) / v;
	float value = coords.x + coords.y;

	vec4 color = texture2D(u_texture, t);

	vec2 center = ((u_uv + u_uv2)/2.0 - u_uv) /v;
	float dst = (abs(center.x - coords.x) + abs(center.y - coords.y)) / 2.0;

    if(dst - 1.0 < u_progress * (center.x) && dst> u_progress * (center.x) && color.a > 0.1){
        gl_FragColor = u_color;
	}else if(cont(t, v, 6.0)){
	    gl_FragColor = color;
	}else if(cont(t, v, 3.0) && color.a > 0.1){
        gl_FragColor = u_color;
    }else{
        gl_FragColor = vec4(0.0);
    }
}