// Doom-style melt wipe, from gl-transitions.com
// Author: Zeh Fernando (MIT)
// Description: the outgoing image melts down in uneven columns, like the Doom
// screen wipe. Fully procedural (no displacement texture).
//
// Ported to ZShell's GLSL ABI (see wallpaper_trans_bowtie.frag). Optional
// gl-transitions params are fixed here: bars = 30, amplitude = 2.0,
// noise = 0.1, frequency = 0.5, dripScale = 0.5.

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 int bars = 30;
const float amplitude = 2.0;
const float noise = 0.1;
const float frequency = 0.5;
const float dripScale = 0.5;

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);
}

float rand(int num) {
	return fract(mod(float(num) * 67123.313, 12.0) * sin(float(num) * 10.3) *
				 cos(float(num)));
}

float wave(int num) {
	float fn = float(num) * frequency * 0.1 * float(bars);
	return cos(fn * 0.5) * cos(fn * 0.13) * sin((fn + 10.0) * 0.3) / 2.0 + 0.5;
}

float drip(int num) {
	return sin(float(num) / float(bars - 1) * 3.141592) * dripScale;
}

float pos(int num) {
	return (noise == 0.0 ? wave(num)
						 : mix(wave(num), rand(num), noise)) +
		   (dripScale == 0.0 ? 0.0 : drip(num));
}

vec4 transition(vec2 uv) {
	int bar = int(uv.x * float(bars));
	float scale = 1.0 + pos(bar) * amplitude;
	float phase = progress * scale;
	float posY = uv.y;

	if (phase + posY < 1.0) {
		return getFromColor(vec2(uv.x, uv.y + phase));
	}
	return getToColor(uv);
}

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