fix: reduce shader usage

Plugins/ZShell/Blobs/shaders/blob.frag

@@ -21,6 +21,7 @@ layout(std140, binding = 0) uniform buf {
   vec4 rectData[80];
   float shadowRadius;
   vec4 shadowColor;
+  vec4 invertedOuterRadii;
 };
 
 float sdRoundedBox(vec2 p, vec2 center, vec2 halfSize, float radius) {
@@ -55,7 +56,8 @@ float smax(float a, float b, float k) {
 
 float smaxSharpA(float a, float b, float k) {
   // smax variant that keeps a's boundary sharp (no inward rounding at a = 0).
-  // Used for the frame outer edge so it always fills to the edges.
+  // Used for the frame inner side, so the outer edge keeps its own shape and
+  // always fills to the edges.
   float h = max(k - abs(a - b), 0.0) / k;
   float blend = h * h * h * k * (1.0 / 6.0);
   blend *= smoothstep(0.0, k * 0.5, -a);
@@ -182,7 +184,12 @@ void main() {
   }
 
   if (hasInverted != 0) {
-    float dOuter = sdBox(pixel, invertedOuter.xy, invertedOuter.zw) - 1.0;
+    // Outer edge rounds with its own per-corner radii. With all-zero radii
+    // sdRoundedBox4 equals sdBox, so a frame that sets no outer radius is
+    // unchanged. smaxSharpA keeps this boundary authoritative for the fill.
+    float dOuter =
+        sdRoundedBox4(pixel, invertedOuter.xy, invertedOuter.zw,
+                      invertedOuterRadii) - 1.0;
     float dInner =
         sdRoundedBox(pixel, invertedInner.xy, invertedInner.zw, invertedRadius);
 
@@ -248,7 +255,13 @@ void main() {
 
     dInner -= sinkValue;
 
-    float dFrame = smaxSharpA(dOuter, -dInner, smoothFactor);
+    // dOuter is already a true circle (sdRoundedBox4). Keep it exact whenever the
+    // outer arc is the active boundary; a smax term added there would pull the
+    // arc's sides inward (curvature/tangent mismatch), so the corner would not be
+    // a circle. Only blend on the inner side, where the inner boundary is active.
+    float negInner = -dInner;
+    float dFrame = dOuter >= negInner ? dOuter
+                                      : smaxSharpA(dOuter, negInner, smoothFactor);
 
     mergedSdf = smin(mergedSdf, dFrame, smoothFactor);
     if (dFrame < minDist) {