// Tiles wave reveal, from gl-transitions.com
// Author: numb3r23 (MIT)
// Description: the incoming image is revealed tile by tile in a diagonal wave.
//
// Ported to ZShell's GLSL ABI (see wallpaper_trans_bowtie.frag).
// Optional gl-transitions params are fixed here: tileCount = (8, 8),
// flipX = true, flipY = false.

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 ivec2 tileCount = ivec2(8, 8);
const bool flipX = true;
const bool flipY = false;

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) {
	vec2 tileSize = 1.0 / vec2(tileCount);
	vec2 posInTile = fract(uv * vec2(tileCount));
	vec2 tileNum = floor(uv * vec2(tileCount));
	float countTiles = float(tileCount.x * tileCount.y);

	// Diagonal wave from bottom-left to top-right.
	float offset = (tileNum.y + tileNum.x * float(tileCount.y)) / countTiles;
	float timeOffset = clamp((progress - offset) * countTiles, 0.0, 0.5);
	float sinTime = 1.0 - abs(cos(fract(timeOffset) * 3.1415926));

	vec2 texC = posInTile;

	if (sinTime <= 0.5) {
		if (flipX) {
			if (texC.x < sinTime || texC.x > 1.0 - sinTime)
				return getFromColor(uv);
			texC.x = texC.x < 0.5
				? (texC.x - sinTime) * 0.5 / (0.5 - sinTime)
				: (texC.x - 0.5) * 0.5 / (0.5 - sinTime) + 0.5;
		}
		if (flipY) {
			if (texC.y < sinTime || texC.y > 1.0 - sinTime)
				return getFromColor(uv);
			texC.y = texC.y < 0.5
				? (texC.y - sinTime) * 0.5 / (0.5 - sinTime)
				: (texC.y - 0.5) * 0.5 / (0.5 - sinTime) + 0.5;
		}
		vec2 globalUV = tileNum * tileSize + texC * tileSize;
		return getFromColor(globalUV);
	} else {
		if (flipX) {
			if (texC.x > sinTime || texC.x < 1.0 - sinTime)
				return getToColor(uv);
			texC.x = texC.x < 0.5
				? (texC.x - sinTime) * 0.5 / (0.5 - sinTime)
				: (texC.x - 0.5) * 0.5 / (0.5 - sinTime) + 0.5;
			texC.x = 1.0 - texC.x;
		}
		if (flipY) {
			if (texC.y > sinTime || texC.y < 1.0 - sinTime)
				return getToColor(uv);
			texC.y = texC.y < 0.5
				? (texC.y - sinTime) * 0.5 / (0.5 - sinTime)
				: (texC.y - 0.5) * 0.5 / (0.5 - sinTime) + 0.5;
			texC.y = 1.0 - texC.y;
		}
		vec2 globalUV = tileNum * tileSize + texC * tileSize;
		return getToColor(globalUV);
	}
}

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