// Bow-tie wipe transition adapted from gl-transitions.com
// Author: huynx (MIT)
// Original: two triangles grow from the top and bottom edges into a bow tie
// that reveals the incoming image.

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;

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 check(vec2 p1, vec2 p2, vec2 p3) {
	return (p1.x - p3.x) * (p2.y - p3.y) - (p2.x - p3.x) * (p1.y - p3.y);
}

bool pointInTriangle(vec2 pt, vec2 p1, vec2 p2, vec2 p3) {
	bool b1 = check(pt, p1, p2) < 0.0;
	bool b2 = check(pt, p2, p3) < 0.0;
	bool b3 = check(pt, p3, p1) < 0.0;
	return (b1 == b2) && (b2 == b3);
}

bool in_top_triangle(vec2 p) {
	vec2 vertex1 = vec2(0.5, progress);
	vec2 vertex2 = vec2(0.5 - progress, 0.0);
	vec2 vertex3 = vec2(0.5 + progress, 0.0);
	return pointInTriangle(p, vertex1, vertex2, vertex3);
}

bool in_bottom_triangle(vec2 p) {
	vec2 vertex1 = vec2(0.5, 1.0 - progress);
	vec2 vertex2 = vec2(0.5 - progress, 1.0);
	vec2 vertex3 = vec2(0.5 + progress, 1.0);
	return pointInTriangle(p, vertex1, vertex2, vertex3);
}

float blur_edge(vec2 bot1, vec2 bot2, vec2 top, vec2 testPt) {
	vec2 lineDir = bot1 - top;
	vec2 perpDir = vec2(lineDir.y, -lineDir.x);
	vec2 dirToPt1 = bot1 - testPt;
	float dist1 = abs(dot(normalize(perpDir), dirToPt1));

	lineDir = bot2 - top;
	perpDir = vec2(lineDir.y, -lineDir.x);
	dirToPt1 = bot2 - testPt;
	float min_dist = min(abs(dot(normalize(perpDir), dirToPt1)), dist1);

	if (min_dist < 0.005)
		return min_dist / 0.005;
	return 1.0;
}

vec4 transition(vec2 uv) {
	if (in_top_triangle(uv)) {
		if (progress < 0.1)
			return getFromColor(uv);

		if (uv.y < 0.5) {
			vec2 vertex1 = vec2(0.5, progress);
			vec2 vertex2 = vec2(0.5 - progress, 0.0);
			vec2 vertex3 = vec2(0.5 + progress, 0.0);
			return mix(
				getFromColor(uv),
				getToColor(uv),
				blur_edge(vertex2, vertex3, vertex1, uv));
		}
		if (progress > 0.0)
			return getToColor(uv);
		return getFromColor(uv);
	}

	if (in_bottom_triangle(uv)) {
		if (uv.y >= 0.5) {
			vec2 vertex1 = vec2(0.5, 1.0 - progress);
			vec2 vertex2 = vec2(0.5 - progress, 1.0);
			vec2 vertex3 = vec2(0.5 + progress, 1.0);
			return mix(
				getFromColor(uv),
				getToColor(uv),
				blur_edge(vertex2, vertex3, vertex1, uv));
		}
		return getFromColor(uv);
	}

	return getFromColor(uv);
}

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