fix(hatch): close the boundary loop in the fill shader

The point-in-polygon test in both hatch shaders walked edges
(v0,v1)…(vn-2,vn-1) but never the closing edge vn-1→v0, so an unclosed
boundary miscounted crossings and the fill bled outside the shape. SOLID
entities hit this — their four corners are not repeated — making color-wheel
fills spike past their bounds. Close each sub-loop (at NaN separators and at
the end); already-closed loops get a degenerate closing edge that crosses
nothing, so they're unaffected. (#140)

Co-Authored-By: Claude Opus 4.8 <[email protected]>

src/shaders/hatch.wgsl

@@ -119,19 +119,34 @@ fn in_polygon(p: vec2<f32>) -> bool {
     var inside = false;
     let n = h.vcount;
     var prev = vec2<f32>(0.0, 0.0);
+    var first = vec2<f32>(0.0, 0.0);
     var have_prev = false;
     for (var i = 0u; i < n; i++) {
         let vi = b.verts[i].xy;
         if !valid_vertex(vi) {
+            // Close the sub-loop that just ended (last → first edge). An
+            // unclosed boundary — e.g. a SOLID's 4 corners, which are not
+            // repeated — otherwise miscounts crossings and the fill bleeds
+            // outside the shape. (#140)
+            if have_prev && edge_crosses(p, prev, first) {
+                inside = !inside;
+            }
             have_prev = false;
             continue;
         }
-        if have_prev && edge_crosses(p, prev, vi) {
-            inside = !inside;
+        if have_prev {
+            if edge_crosses(p, prev, vi) {
+                inside = !inside;
+            }
+        } else {
+            first = vi;
         }
         prev = vi;
         have_prev = true;
     }
+    if have_prev && edge_crosses(p, prev, first) {
+        inside = !inside;
+    }
     return inside;
 }
 

src/shaders/hatch_batched.wgsl

@@ -150,19 +150,34 @@ fn edge_crosses(p: vec2<f32>, a: vec2<f32>, c: vec2<f32>) -> bool {
 fn in_polygon(p: vec2<f32>, offset: u32, count: u32) -> bool {
     var inside = false;
     var prev = vec2<f32>(0.0, 0.0);
+    var first = vec2<f32>(0.0, 0.0);
     var have_prev = false;
     for (var i = 0u; i < count; i++) {
         let vi = boundary[offset + i].xy;
         if !valid_vertex(vi) {
+            // Close the sub-loop that just ended (last → first edge). An
+            // unclosed boundary — e.g. a SOLID's 4 corners, which are not
+            // repeated — otherwise miscounts crossings and the fill bleeds
+            // outside the shape. (#140)
+            if have_prev && edge_crosses(p, prev, first) {
+                inside = !inside;
+            }
             have_prev = false;
             continue;
         }
-        if have_prev && edge_crosses(p, prev, vi) {
-            inside = !inside;
+        if have_prev {
+            if edge_crosses(p, prev, vi) {
+                inside = !inside;
+            }
+        } else {
+            first = vi;
         }
         prev = vi;
         have_prev = true;
     }
+    if have_prev && edge_crosses(p, prev, first) {
+        inside = !inside;
+    }
     return inside;
 }