Add wallpaper transition effects, courtesy of @Ly-Sec

- Just copied the shaders from noctalia since they're pretty awesome

Shaders/frag/wp_disc.frag

@@ -0,0 +1,122 @@
+// ===== wp_disc.frag =====
+#version 450
+
+layout(location = 0) in vec2 qt_TexCoord0;
+layout(location = 0) out vec4 fragColor;
+
+layout(binding = 1) uniform sampler2D source1;  // Current wallpaper
+layout(binding = 2) uniform sampler2D source2;  // Next wallpaper
+
+layout(std140, binding = 0) uniform buf {
+    mat4 qt_Matrix;
+    float qt_Opacity;
+    float progress;      // Transition progress (0.0 to 1.0)
+    float centerX;       // X coordinate of disc center (0.0 to 1.0)
+    float centerY;       // Y coordinate of disc center (0.0 to 1.0)
+    float smoothness;    // Edge smoothness (0.0 to 1.0, 0=sharp, 1=very smooth)
+    float aspectRatio;   // Width / Height of the screen
+    
+    // Fill mode parameters
+    float fillMode;      // 0=no(center), 1=crop(fill), 2=fit(contain), 3=stretch
+    float imageWidth1;   // Width of source1 image
+    float imageHeight1;  // Height of source1 image
+    float imageWidth2;   // Width of source2 image
+    float imageHeight2;  // Height of source2 image
+    float screenWidth;   // Screen width
+    float screenHeight;  // Screen height
+    vec4 fillColor;      // Fill color for empty areas (default: black)
+} ubuf;
+
+// Calculate UV coordinates based on fill mode
+vec2 calculateUV(vec2 uv, float imgWidth, float imgHeight) {
+    float imageAspect = imgWidth / imgHeight;
+    float screenAspect = ubuf.screenWidth / ubuf.screenHeight;
+    vec2 transformedUV = uv;
+    
+    if (ubuf.fillMode < 0.5) {
+        // Mode 0: no (center) - No resize, center image at original size
+        // Convert UV to pixel coordinates, offset, then back to UV in image space
+        vec2 screenPixel = uv * vec2(ubuf.screenWidth, ubuf.screenHeight);
+        vec2 imageOffset = (vec2(ubuf.screenWidth, ubuf.screenHeight) - vec2(imgWidth, imgHeight)) * 0.5;
+        vec2 imagePixel = screenPixel - imageOffset;
+        transformedUV = imagePixel / vec2(imgWidth, imgHeight);
+    } 
+    else if (ubuf.fillMode < 1.5) {
+        // Mode 1: crop (fill/cover) - Fill screen, crop excess (default)
+        float scale = max(ubuf.screenWidth / imgWidth, ubuf.screenHeight / imgHeight);
+        vec2 scaledImageSize = vec2(imgWidth, imgHeight) * scale;
+        vec2 offset = (scaledImageSize - vec2(ubuf.screenWidth, ubuf.screenHeight)) / scaledImageSize;
+        transformedUV = uv * (vec2(1.0) - offset) + offset * 0.5;
+    }
+    else if (ubuf.fillMode < 2.5) {
+        // Mode 2: fit (contain) - Fit inside screen, maintain aspect ratio
+        float scale = min(ubuf.screenWidth / imgWidth, ubuf.screenHeight / imgHeight);
+        vec2 scaledImageSize = vec2(imgWidth, imgHeight) * scale;
+        vec2 offset = (vec2(ubuf.screenWidth, ubuf.screenHeight) - scaledImageSize) * 0.5;
+        
+        // Convert screen UV to pixel coordinates
+        vec2 screenPixel = uv * vec2(ubuf.screenWidth, ubuf.screenHeight);
+        // Adjust for offset and scale
+        vec2 imagePixel = (screenPixel - offset) / scale;
+        // Convert back to UV coordinates in image space
+        transformedUV = imagePixel / vec2(imgWidth, imgHeight);
+    }
+    // Mode 3: stretch - Use original UV (stretches to fit)
+    // No transformation needed for stretch mode
+    
+    return transformedUV;
+}
+
+// Sample texture with fill mode and handle out-of-bounds
+vec4 sampleWithFillMode(sampler2D tex, vec2 uv, float imgWidth, float imgHeight) {
+    vec2 transformedUV = calculateUV(uv, imgWidth, imgHeight);
+    
+    // Check if UV is out of bounds
+    if (transformedUV.x < 0.0 || transformedUV.x > 1.0 || 
+        transformedUV.y < 0.0 || transformedUV.y > 1.0) {
+        return ubuf.fillColor;
+    }
+    
+    return texture(tex, transformedUV);
+}
+
+void main() {
+    vec2 uv = qt_TexCoord0;
+
+    // Sample textures with fill mode
+    vec4 color1 = sampleWithFillMode(source1, uv, ubuf.imageWidth1, ubuf.imageHeight1);
+    vec4 color2 = sampleWithFillMode(source2, uv, ubuf.imageWidth2, ubuf.imageHeight2);
+
+    // Map smoothness from 0.0-1.0 to 0.001-0.5 range
+    // Using a non-linear mapping for better control
+    float mappedSmoothness = mix(0.001, 0.5, ubuf.smoothness * ubuf.smoothness);
+
+    // Adjust UV coordinates to compensate for aspect ratio
+    // This makes distances circular instead of elliptical
+    vec2 adjustedUV = vec2(uv.x * ubuf.aspectRatio, uv.y);
+    vec2 adjustedCenter = vec2(ubuf.centerX * ubuf.aspectRatio, ubuf.centerY);
+    
+    // Calculate distance in aspect-corrected space
+    float dist = distance(adjustedUV, adjustedCenter);
+    
+    // Calculate the maximum possible distance (corner to corner)
+    // This ensures the disc can cover the entire screen
+    float maxDistX = max(ubuf.centerX * ubuf.aspectRatio, 
+                         (1.0 - ubuf.centerX) * ubuf.aspectRatio);
+    float maxDistY = max(ubuf.centerY, 1.0 - ubuf.centerY);
+    float maxDist = length(vec2(maxDistX, maxDistY));
+    
+    // Scale progress to cover the maximum distance
+    // Add extra range for smoothness to ensure complete coverage
+    // Adjust smoothness for aspect ratio to maintain consistent visual appearance
+    float adjustedSmoothness = mappedSmoothness * max(1.0, ubuf.aspectRatio);
+    float radius = ubuf.progress * (maxDist + adjustedSmoothness);
+    
+    // Use smoothstep for a smooth edge transition
+    float factor = smoothstep(radius - adjustedSmoothness, radius + adjustedSmoothness, dist);
+    
+    // Mix the textures (factor = 0 inside disc, 1 outside)
+    fragColor = mix(color2, color1, factor);
+    
+    fragColor *= ubuf.qt_Opacity;
+}