fix #199 - handle small arcs with rounded corners

d3 · Dec 20, 2022 · 439713e · 439713e
1 parent 8fe68eb
commit 439713e
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Showing 2 changed files with 21 additions and 10 deletions.
diff --git a/src/arc.js b/src/arc.js
@@ -152,16 +152,22 @@ export default function() {
             y00 = r0 * sin(a00),
             oc;
 
-        // Restrict the corner radius according to the sector angle.
-        if (da < pi && (oc = intersect(x01, y01, x00, y00, x11, y11, x10, y10))) {
-          var ax = x01 - oc[0],
-              ay = y01 - oc[1],
-              bx = x11 - oc[0],
-              by = y11 - oc[1],
-              kc = 1 / sin(acos((ax * bx + ay * by) / (sqrt(ax * ax + ay * ay) * sqrt(bx * bx + by * by))) / 2),
-              lc = sqrt(oc[0] * oc[0] + oc[1] * oc[1]);
-          rc0 = min(rc, (r0 - lc) / (kc - 1));
-          rc1 = min(rc, (r1 - lc) / (kc + 1));
+        // Restrict the corner radius according to the sector angle. If this
+        // intersection fails, it’s probably because the arc is too small, so
+        // disable the corner radius entirely.
+        if (da < pi) {
+          if (oc = intersect(x01, y01, x00, y00, x11, y11, x10, y10)) {
+            var ax = x01 - oc[0],
+                ay = y01 - oc[1],
+                bx = x11 - oc[0],
+                by = y11 - oc[1],
+                kc = 1 / sin(acos((ax * bx + ay * by) / (sqrt(ax * ax + ay * ay) * sqrt(bx * bx + by * by))) / 2),
+                lc = sqrt(oc[0] * oc[0] + oc[1] * oc[1]);
+            rc0 = min(rc, (r0 - lc) / (kc - 1));
+            rc1 = min(rc, (r1 - lc) / (kc + 1));
+          } else {
+            rc0 = rc1 = 0;
+          }
         }
       }
 

diff --git a/test/arc-test.js b/test/arc-test.js
@@ -360,3 +360,8 @@ it("arc().innerRadius(r₀).outerRadius(r₁).startAngle(θ₀).endAngle(θ₁).
   const a = arc().innerRadius(10).outerRadius(100).startAngle(0).endAngle(Math.PI / 2).padAngle(0.2).cornerRadius(10);
   assertPathEqual(a(), "M9.669396,-88.145811A10,10,0,0,1,21.849183,-97.583878A100,100,0,0,1,97.583878,-21.849183A10,10,0,0,1,88.145811,-9.669396L7.071068,-7.071068Z");
 });
+
+it("arc() handles a very small arc with rounded corners", () => {
+  const a = arc().innerRadius(15).outerRadius(24).padAngle(0).startAngle(1.2 - 1e-8).endAngle(1.2).cornerRadius(4);
+  assertPathEqual(a(), "M22.369,-8.697L13.981,-5.435Z");
+});