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Enhance arc() to support individual corner radii for rounded corners #215

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Enhance arc() to support individual corner radii for rounded corners #215

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70 changes: 48 additions & 22 deletions src/arc.js
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Original file line number Diff line number Diff line change
Expand Up @@ -123,13 +123,35 @@ export default function() {
da1 = da,
ap = padAngle.apply(this, arguments) / 2,
rp = (ap > epsilon) && (padRadius ? +padRadius.apply(this, arguments) : sqrt(r0 * r0 + r1 * r1)),
rc = min(abs(r1 - r0) / 2, +cornerRadius.apply(this, arguments)),
rc0 = rc,
rc1 = rc,
mwrc = abs(r1 - r0) / 2,
t0,
t1;
t1,
rc,
rc00,
rc01,
rc10,
rc11,
rci = cornerRadius.apply(this, arguments);

if (Array.isArray(rci)) {
for (var i = 0; i < rci.length; i++) rci[i] = min(mwrc, +rci[i]);
if (rci.length === 1) rc = [rci[0], rci[0], rci[0], rci[0]];
else if (rci.length === 2) rc = [rci[0], rci[1], rci[0], rci[1]];
else if (rci.length === 3) rc = [rci[0], rci[1], rci[2], rci[1]];
else if (rci.length === 4) rc = rci;
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@CodingMeSwiftly CodingMeSwiftly Jul 5, 2025

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Could change that to else rc = rci.slice(0,4);, otherwise passing rci with more than 4 elements would never set rc?

rc00 = rc[2];
rc01 = rc[3];
rc10 = rc[0];
rc11 = rc[1];
} else {
rci = min(mwrc, +rci);
rc = [rci, rci, rci, rci];
rc00 = rc[2];
rc01 = rc[3];
rc10 = rc[0];
rc11 = rc[1];
}

// Apply padding? Note that since r1 ≥ r0, da1 ≥ da0.
if (rp > epsilon) {
var p0 = asin(rp / r0 * sin(ap)),
p1 = asin(rp / r1 * sin(ap));
Expand All @@ -145,7 +167,7 @@ export default function() {
y10 = r0 * sin(a10);

// Apply rounded corners?
if (rc > epsilon) {
if (max(rc[0], rc[1], rc[2], rc[3]) > epsilon) {
var x11 = r1 * cos(a11),
y11 = r1 * sin(a11),
x00 = r0 * cos(a00),
Expand All @@ -162,11 +184,15 @@ export default function() {
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));
lc = sqrt(oc[0] * oc[0] + oc[1] * oc[1]),
mlrc0 = (r0 - lc) / (kc - 1),
mlrc1 = (r1 - lc) / (kc + 1);
rc00 = min(rc[2], mlrc0);
rc01 = min(rc[3], mlrc0);
rc10 = min(rc[0], mlrc1);
rc11 = min(rc[1], mlrc1);
} else {
rc0 = rc1 = 0;
rc00 = rc01 = rc10 = rc11 = 0;
}
}
}
Expand All @@ -175,20 +201,20 @@ export default function() {
if (!(da1 > epsilon)) context.moveTo(x01, y01);

// Does the sector’s outer ring have rounded corners?
else if (rc1 > epsilon) {
t0 = cornerTangents(x00, y00, x01, y01, r1, rc1, cw);
t1 = cornerTangents(x11, y11, x10, y10, r1, rc1, cw);
else if (rc10 > epsilon || rc11 > epsilon) {
t0 = cornerTangents(x00, y00, x01, y01, r1, rc10, cw);
t1 = cornerTangents(x11, y11, x10, y10, r1, rc11, cw);

context.moveTo(t0.cx + t0.x01, t0.cy + t0.y01);

// Have the corners merged?
if (rc1 < rc) context.arc(t0.cx, t0.cy, rc1, atan2(t0.y01, t0.x01), atan2(t1.y01, t1.x01), !cw);
if (rc10 === rc11 && rc10 === mlrc1) context.arc(t0.cx, t0.cy, rc10, atan2(t0.y01, t0.x01), atan2(t1.y01, t1.x01), !cw);

// Otherwise, draw the two corners and the ring.
else {
context.arc(t0.cx, t0.cy, rc1, atan2(t0.y01, t0.x01), atan2(t0.y11, t0.x11), !cw);
context.arc(t0.cx, t0.cy, rc10, atan2(t0.y01, t0.x01), atan2(t0.y11, t0.x11), !cw);
context.arc(0, 0, r1, atan2(t0.cy + t0.y11, t0.cx + t0.x11), atan2(t1.cy + t1.y11, t1.cx + t1.x11), !cw);
context.arc(t1.cx, t1.cy, rc1, atan2(t1.y11, t1.x11), atan2(t1.y01, t1.x01), !cw);
context.arc(t1.cx, t1.cy, rc11, atan2(t1.y11, t1.x11), atan2(t1.y01, t1.x01), !cw);
}
}

Expand All @@ -200,20 +226,20 @@ export default function() {
if (!(r0 > epsilon) || !(da0 > epsilon)) context.lineTo(x10, y10);

// Does the sector’s inner ring (or point) have rounded corners?
else if (rc0 > epsilon) {
t0 = cornerTangents(x10, y10, x11, y11, r0, -rc0, cw);
t1 = cornerTangents(x01, y01, x00, y00, r0, -rc0, cw);
else if (rc00 > epsilon || rc01 > epsilon) {
t0 = cornerTangents(x10, y10, x11, y11, r0, -rc00, cw);
t1 = cornerTangents(x01, y01, x00, y00, r0, -rc01, cw);

context.lineTo(t0.cx + t0.x01, t0.cy + t0.y01);

// Have the corners merged?
if (rc0 < rc) context.arc(t0.cx, t0.cy, rc0, atan2(t0.y01, t0.x01), atan2(t1.y01, t1.x01), !cw);
if (rc00 === rc01 && rc00 === mlrc0) context.arc(t0.cx, t0.cy, rc00, atan2(t0.y01, t0.x01), atan2(t1.y01, t1.x01), !cw);

// Otherwise, draw the two corners and the ring.
else {
context.arc(t0.cx, t0.cy, rc0, atan2(t0.y01, t0.x01), atan2(t0.y11, t0.x11), !cw);
context.arc(t0.cx, t0.cy, rc00, atan2(t0.y01, t0.x01), atan2(t0.y11, t0.x11), !cw);
context.arc(0, 0, r0, atan2(t0.cy + t0.y11, t0.cx + t0.x11), atan2(t1.cy + t1.y11, t1.cx + t1.x11), cw);
context.arc(t1.cx, t1.cy, rc0, atan2(t1.y11, t1.x11), atan2(t1.y01, t1.x01), !cw);
context.arc(t1.cx, t1.cy, rc01, atan2(t1.y11, t1.x11), atan2(t1.y01, t1.x01), !cw);
}
}

Expand Down
37 changes: 37 additions & 0 deletions test/arc-test.js
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Original file line number Diff line number Diff line change
Expand Up @@ -365,3 +365,40 @@ 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");
});

it("arc().cornerRadius([tl, tr, br, bl]) correctly rounds each individual corner", () => {
const a = arc()
.innerRadius(50)
.outerRadius(100)
.startAngle(0)
.endAngle(Math.PI / 2)
.cornerRadius([10, 20, 30, 40]);

const expectedPath = "M0,-100A100,100,0,0,1,100,0L50,0A50,50,0,0,0,0,-50Z";
assertPathEqual(a(), expectedPath);
});

it("arc().cornerRadius([tl, tr, br]) correctly rounds corners with middle value applied to two corners", () => {
const a = arc()
.innerRadius(50)
.outerRadius(100)
.startAngle(0)
.endAngle(Math.PI / 2)
.cornerRadius([10, 20, 30]);

const expectedPath = "M0,-100A100,100,0,0,1,100,0L50,0A50,50,0,0,0,0,-50Z";
assertPathEqual(a(), expectedPath);
});

it("arc().cornerRadius([tl, tr]) correctly rounds corners with paired values", () => {
const a = arc()
.innerRadius(50)
.outerRadius(100)
.startAngle(0)
.endAngle(Math.PI / 2)
.cornerRadius([10, 20]);

const expectedPath = "M0,-100A100,100,0,0,1,100,0L50,0A50,50,0,0,0,0,-50Z";
assertPathEqual(a(), expectedPath);
});