// Copyright (C) 2026 Danilo M. <danix@danix.xyz>
//
// This program is free software; you can redistribute it and/or modify
// it under the terms of the GNU General Public License version 2 as
// published by the Free Software Foundation.
//
// This program is distributed in the hope that it will be useful,
// but WITHOUT ANY WARRANTY; without even the implied warranty of
// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
// GNU General Public License for more details.

// The old wallpaper running down the screen like wet paint, each column
// starting late by its noise and accelerating. Compiled with:
// qsb --qt6 -o melt.frag.qsb melt.frag
#version 440
layout(location = 0) in vec2 qt_TexCoord0;
layout(location = 0) out vec4 fragColor;
layout(std140, binding = 0) uniform buf {
    mat4 qt_Matrix;
    float qt_Opacity;
    float progress;
    float aspect;
};
layout(binding = 1) uniform sampler2D source;

float hash(vec2 p) { return fract(sin(dot(p, vec2(12.9898, 78.233))) * 43758.5453); }

float noise(vec2 p) {
    vec2 i = floor(p), f = fract(p);
    vec2 u = f * f * (3.0 - 2.0 * f);
    return mix(mix(hash(i), hash(i + vec2(1, 0)), u.x),
               mix(hash(i + vec2(0, 1)), hash(i + vec2(1, 1)), u.x), u.y);
}

void main() {
    float x = qt_TexCoord0.x * aspect;
    float delay = 0.25 * (noise(vec2(x * 40.0, 0.0)) + noise(vec2(x * 9.0, 3.0)));
    float l = clamp((progress - delay) / 0.5, 0.0, 1.0);

    // Past 1, so the bottom row clears the screen.
    vec2 uv = vec2(qt_TexCoord0.x, qt_TexCoord0.y - l * l * 1.02);
    float a = smoothstep(-0.004, 0.0, uv.y);
    fragColor = vec4(texture(source, uv).rgb * a, a) * qt_Opacity;
}