From ac8edbaf4163fd7e0934b72175d60e71844d8cf9 Mon Sep 17 00:00:00 2001
From: Bogdan Chadkin <trysound@yandex.ru>
Date: Fri, 27 Aug 2021 01:03:11 +0300
Subject: [PATCH] Fix applying transform to arc with zero radius

Ref https://github.com/svg/svgo/issues/1500
---
 plugins/_transforms.js              | 52 +++++++++++++++--------------
 test/plugins/convertPathData.26.svg | 13 ++++++++
 2 files changed, 40 insertions(+), 25 deletions(-)
 create mode 100644 test/plugins/convertPathData.26.svg

diff --git a/plugins/_transforms.js b/plugins/_transforms.js
index dcd4db0f..159f1a3b 100644
--- a/plugins/_transforms.js
+++ b/plugins/_transforms.js
@@ -309,40 +309,42 @@ const transformToMatrix = (transform) => {
 exports.transformArc = (cursor, arc, transform) => {
   const x = arc[5] - cursor[0];
   const y = arc[6] - cursor[1];
-  var a = arc[0],
-    b = arc[1],
-    rot = (arc[2] * Math.PI) / 180,
-    cos = Math.cos(rot),
-    sin = Math.sin(rot),
-    h =
+  let a = arc[0];
+  let b = arc[1];
+  const rot = (arc[2] * Math.PI) / 180;
+  const cos = Math.cos(rot);
+  const sin = Math.sin(rot);
+  // skip if radius is 0
+  if (a > 0 && b > 0) {
+    let h =
       Math.pow(x * cos + y * sin, 2) / (4 * a * a) +
       Math.pow(y * cos - x * sin, 2) / (4 * b * b);
-  if (h > 1) {
-    h = Math.sqrt(h);
-    a *= h;
-    b *= h;
+    if (h > 1) {
+      h = Math.sqrt(h);
+      a *= h;
+      b *= h;
+    }
   }
-  var ellipse = [a * cos, a * sin, -b * sin, b * cos, 0, 0],
-    m = multiplyTransformMatrices(transform, ellipse),
-    // Decompose the new ellipse matrix
-    lastCol = m[2] * m[2] + m[3] * m[3],
-    squareSum = m[0] * m[0] + m[1] * m[1] + lastCol,
-    root =
-      Math.hypot(m[0] - m[3], m[1] + m[2]) *
-      Math.hypot(m[0] + m[3], m[1] - m[2]);
+  const ellipse = [a * cos, a * sin, -b * sin, b * cos, 0, 0];
+  const m = multiplyTransformMatrices(transform, ellipse);
+  // Decompose the new ellipse matrix
+  const lastCol = m[2] * m[2] + m[3] * m[3];
+  const squareSum = m[0] * m[0] + m[1] * m[1] + lastCol;
+  const root =
+    Math.hypot(m[0] - m[3], m[1] + m[2]) * Math.hypot(m[0] + m[3], m[1] - m[2]);
 
   if (!root) {
     // circle
     arc[0] = arc[1] = Math.sqrt(squareSum / 2);
     arc[2] = 0;
   } else {
-    var majorAxisSqr = (squareSum + root) / 2,
-      minorAxisSqr = (squareSum - root) / 2,
-      major = Math.abs(majorAxisSqr - lastCol) > 1e-6,
-      sub = (major ? majorAxisSqr : minorAxisSqr) - lastCol,
-      rowsSum = m[0] * m[2] + m[1] * m[3],
-      term1 = m[0] * sub + m[2] * rowsSum,
-      term2 = m[1] * sub + m[3] * rowsSum;
+    const majorAxisSqr = (squareSum + root) / 2;
+    const minorAxisSqr = (squareSum - root) / 2;
+    const major = Math.abs(majorAxisSqr - lastCol) > 1e-6;
+    const sub = (major ? majorAxisSqr : minorAxisSqr) - lastCol;
+    const rowsSum = m[0] * m[2] + m[1] * m[3];
+    const term1 = m[0] * sub + m[2] * rowsSum;
+    const term2 = m[1] * sub + m[3] * rowsSum;
     arc[0] = Math.sqrt(majorAxisSqr);
     arc[1] = Math.sqrt(minorAxisSqr);
     arc[2] =
diff --git a/test/plugins/convertPathData.26.svg b/test/plugins/convertPathData.26.svg
new file mode 100644
index 00000000..968bab1f
--- /dev/null
+++ b/test/plugins/convertPathData.26.svg
@@ -0,0 +1,13 @@
+Applying transform to arc with zero radius should not produce NaNs
+
+===
+
+<svg xmlns="http://www.w3.org/2000/svg" viewBox="0 0 31.6 31.6">
+  <path d="m5.25,2.2H25.13a0,0,0,0,1-.05-.05V14.18Z" transform="translate(0 0)"/>
+</svg>
+
+@@@
+
+<svg xmlns="http://www.w3.org/2000/svg" viewBox="0 0 31.6 31.6">
+    <path d="M5.25 2.2h19.88l-.05-.05v12.03Z"/>
+</svg>