// Linear blur crossfade, from gl-transitions.com
// Author: gre (MIT)
// Description: a crossfade that passes through a directional blur.
//
// Ported to ZShell's GLSL ABI (see wallpaper_trans_bowtie.frag): the version
// header is prepended by WallpaperService::shaderSource, the fullscreen
// triangle comes from wallpaper.vert, and getFromColor/getToColor apply the
// crop + flip convention. `uv` is bottom-left origin per gl-transitions.
//
// Optional gl-transitions params are fixed here: intensity = 0.1.

uniform sampler2D from;
uniform sampler2D to;
uniform vec2 size;
uniform vec4 fromCrop;
uniform vec4 toCrop;
uniform float progress;
uniform float fromFlip;
uniform float toFlip;

out vec4 outColor;

const float intensity = 0.1;
const int passes = 6;

vec4 getFromColor(vec2 uv) {
	vec2 s = vec2(uv.x, fromFlip > 0.5 ? 1.0 - uv.y : uv.y);
	return texture(from, fromCrop.xy + s * fromCrop.zw);
}

vec4 getToColor(vec2 uv) {
	vec2 s = vec2(uv.x, toFlip > 0.5 ? 1.0 - uv.y : uv.y);
	return texture(to, toCrop.xy + s * toCrop.zw);
}

vec4 transition(vec2 uv) {
	vec4 c1 = vec4(0.0);
	vec4 c2 = vec4(0.0);

	float disp = intensity * (0.5 - distance(0.5, progress));
	for (int xi = 0; xi < passes; xi++) {
		float x = float(xi) / float(passes) - 0.5;
		for (int yi = 0; yi < passes; yi++) {
			float y = float(yi) / float(passes) - 0.5;
			vec2 v = vec2(x, y);
			c1 += getFromColor(uv + disp * v);
			c2 += getToColor(uv + disp * v);
		}
	}
	c1 /= float(passes * passes);
	c2 /= float(passes * passes);
	return mix(c1, c2, progress);
}

void main() {
	vec2 uv = gl_FragCoord.xy / size;
	outColor = transition(uv);
}