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// 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 dissolving like ink in water: a soft edge through noise
// warped by more noise, the picture smearing as it goes. Compiled with:
// qsb --qt6 -o ink.frag.qsb ink.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);
}
float fbm(vec2 p) {
float v = 0.0, a = 0.5;
for (int i = 0; i < 5; i++) { v += a * noise(p); p *= 2.03; a *= 0.5; }
return v;
}
void main() {
vec2 p = qt_TexCoord0 * vec2(aspect, 1.0);
vec2 warp = vec2(fbm(p * 3.0 + progress), fbm(p * 3.0 + 7.3 - progress));
// fbm sits around 0.2 to 0.8; stretched and clamped, so the edge below
// sweeps past every pixel.
float t = clamp((fbm(p * 2.0 + warp * 1.5) - 0.2) / 0.6, 0.0, 1.0);
const float w = 0.15;
float a = smoothstep(0.0, w, t - mix(-w, 1.0, progress));
vec2 uv = qt_TexCoord0 + (warp - 0.5) * 0.04 * (1.0 - a);
fragColor = vec4(texture(source, uv).rgb * a, a) * qt_Opacity;
}
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