wallpaper: six more transitions

Ink, shatter, ripple, melt, blinds and cross-warp. Each draws the old
picture exactly at progress 0 and the new one at 1, or the cover would
pop as it comes and goes: rendered under Xvfb with llvmpipe against the
plain pictures, all seven differ by 0 at both ends. Ripple and cross-warp
sample the new picture, the rest are transparent over it.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

1 files changed, 39 insertions, 0 deletions

diff --git a/desktop/modules/appearance/blinds.frag b/desktop/modules/appearance/blinds.frag
new file mode 100644
index 0000000..49ee17b
--- /dev/null
+++ b/desktop/modules/appearance/blinds.frag
@@ -0,0 +1,39 @@
+// 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.
+
+// Vertical slats turning edge-on in a wave from a random column, darkening as
+// they turn, with the new wallpaper between them. Compiled with:
+// qsb --qt6 -o blinds.frag.qsb blinds.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;
+    vec2 origin;
+};
+layout(binding = 1) uniform sampler2D source;
+
+void main() {
+    const float n = 16.0;
+    float slat = floor(qt_TexCoord0.x * n);
+    float f = fract(qt_TexCoord0.x * n) - 0.5;
+
+    float wave = abs((slat + 0.5) / n - origin.x) / max(origin.x, 1.0 - origin.x);
+    float l = clamp((progress - 0.6 * min(wave, 1.0)) / 0.4, 0.0, 1.0);
+
+    float half_ = 0.5 * cos(l * 1.5708);
+    if (l >= 1.0 || abs(f) > half_) { fragColor = vec4(0.0); return; }
+
+    vec2 uv = vec2((slat + 0.5 + f * 0.5 / half_) / n, qt_TexCoord0.y);
+    fragColor = vec4(texture(source, uv).rgb * mix(1.0, 0.55, l), 1.0) * qt_Opacity;
+}