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, 37 insertions, 0 deletions

diff --git a/desktop/modules/appearance/crosswarp.frag b/desktop/modules/appearance/crosswarp.frag
new file mode 100644
index 0000000..d7fc91a
--- /dev/null
+++ b/desktop/modules/appearance/crosswarp.frag
@@ -0,0 +1,37 @@
+// 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.
+
+// Both pictures pulled away from a random point by their own brightness,
+// flowing into each other: the old one stretches as it leaves, the new one
+// settles as it arrives. Opaque throughout. Compiled with:
+// qsb --qt6 -o crosswarp.frag.qsb crosswarp.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;
+layout(binding = 2) uniform sampler2D target;
+
+float luma(vec3 c) { return dot(c, vec3(0.299, 0.587, 0.114)); }
+
+void main() {
+    vec2 uv = qt_TexCoord0;
+    vec2 dir = uv - origin;
+    float x = smoothstep(0.0, 1.0, progress);
+    vec2 ua = uv + dir * luma(texture(source, uv).rgb) * x * 0.3;
+    vec2 ub = uv - dir * luma(texture(target, uv).rgb) * (1.0 - x) * 0.3;
+    fragColor = vec4(mix(texture(source, ua).rgb, texture(target, ub).rgb, x), 1.0) * qt_Opacity;
+}