shaders/roundedcorners: base on kde-rounded-corners' shader

src/shaders/roundedcorners.glsl

@@ -1,30 +1,42 @@
+// Based on KDE-Rounded-Corners' shader: https://github.com/matinlotfali/KDE-Rounded-Corners/blob/master/src/shaders/shapecorners.glsl
+
 uniform float topCornerRadius;
 uniform float bottomCornerRadius;
 uniform float antialiasing;
 
 uniform vec2 blurSize;
 uniform float opacity;
 
+vec4 shapeCorner(vec2 coord0, vec3 tex, vec2 start, float angle, float r) {
+    float diagonal_length = (abs(cos(angle)) > 0.1 && abs(sin(angle)) > 0.1) ? sqrt(2.0) : 1.0;
+    vec2 center = start + r * diagonal_length * vec2(cos(angle), sin(angle));
+    float distance_from_center = distance(coord0, center);
+
+    // I don't know exactly where the 0.25 comes from, in the original shader it's 0.5 but doesn't look perfect
+    float antialiasing = clamp(r - distance_from_center + 0.25, 0.0, 1.0);
+    return vec4(tex, mix(0.0, 1.0, antialiasing) * opacity);
+}
+
 vec4 roundedRectangle(vec2 fragCoord, vec3 texture)
 {
     if (topCornerRadius == 0 && bottomCornerRadius == 0) {
         return vec4(texture, opacity);
     }
 
-    vec2 halfblurSize = blurSize * 0.5;
-    vec2 p = fragCoord - halfblurSize;
-    float radius = 0.0;
-    if ((fragCoord.y <= bottomCornerRadius)
-        && (fragCoord.x <= bottomCornerRadius || fragCoord.x >= blurSize.x - bottomCornerRadius)) {
-        radius = bottomCornerRadius;
-        p.y -= radius;
-    } else if ((fragCoord.y >= blurSize.y - topCornerRadius)
-        && (fragCoord.x <= topCornerRadius || fragCoord.x >= blurSize.x - topCornerRadius)) {
-        radius = topCornerRadius;
-        p.y += radius;
+    if (fragCoord.y < bottomCornerRadius) {
+        if (fragCoord.x < bottomCornerRadius) {
+            return shapeCorner(fragCoord, texture, vec2(0.0, 0.0), radians(45.0), bottomCornerRadius);
+        } else if (fragCoord.x > blurSize.x - bottomCornerRadius) {
+            return shapeCorner(fragCoord, texture, vec2(blurSize.x, 0.0), radians(135.0), bottomCornerRadius);
+        }
+    }
+    else if (fragCoord.y > blurSize.y - topCornerRadius) {
+        if (fragCoord.x < topCornerRadius) {
+            return shapeCorner(fragCoord, texture, vec2(0.0, blurSize.y), radians(315.0), topCornerRadius);
+        } else if (fragCoord.x > blurSize.x - topCornerRadius) {
+            return shapeCorner(fragCoord, texture, vec2(blurSize.x, blurSize.y), radians(225.0), topCornerRadius);
+        }
     }
-    float distance = length(max(abs(p) - (halfblurSize + vec2(0.0, radius)) + radius, 0.0)) - radius;
 
-    float s = smoothstep(0.0, antialiasing, distance);
-    return vec4(texture, mix(1.0, 0.0, s) * opacity);
+    return vec4(texture, opacity);
 }