feat(convertPathData): convert c to q (#1892)

docs/03-plugins/convert-path-data.mdx

@@ -15,6 +15,9 @@ svgo:
     straightCurves:
       description: If to convert curve commands that are effectively straight lines to line commands.
       default: true
+    convertToQ:
+      description: If to convert cubic beziers to quadratic beziers when they effectively are.
+      default: true
     lineShorthands:
       description: If to convert regular lines to an explicit horizontal or vertical line where possible.
       default: true

plugins/convertPathData.js

@@ -35,6 +35,7 @@ let arcTolerance;
  *     tolerance: number,
  *   },
  *   straightCurves: boolean,
+ *   convertToQ: boolean,
  *   lineShorthands: boolean,
  *   convertToZ: boolean,
  *   curveSmoothShorthands: boolean,
@@ -86,6 +87,7 @@ exports.fn = (root, params) => {
       tolerance: 0.5, // percentage of radius
     },
     straightCurves = true,
+    convertToQ = true,
     lineShorthands = true,
     convertToZ = true,
     curveSmoothShorthands = true,
@@ -109,6 +111,7 @@ exports.fn = (root, params) => {
     applyTransformsStroked,
     makeArcs,
     straightCurves,
+    convertToQ,
     lineShorthands,
     convertToZ,
     curveSmoothShorthands,
@@ -674,6 +677,44 @@ function filters(
         }
       }
 
+      // degree-lower c to q when possible
+      // m 0 12 C 4 4 8 4 12 12 → M 0 12 Q 6 0 12 12
+      if (params.convertToQ && command == 'c') {
+        const x1 =
+          // @ts-ignore
+          0.75 * (item.base[0] + data[0]) - 0.25 * item.base[0];
+        const x2 =
+          // @ts-ignore
+          0.75 * (item.base[0] + data[2]) - 0.25 * (item.base[0] + data[4]);
+        if (Math.abs(x1 - x2) < error * 2) {
+          const y1 =
+            // @ts-ignore
+            0.75 * (item.base[1] + data[1]) - 0.25 * item.base[1];
+          const y2 =
+            // @ts-ignore
+            0.75 * (item.base[1] + data[3]) - 0.25 * (item.base[1] + data[5]);
+          if (Math.abs(y1 - y2) < error * 2) {
+            const newData = data.slice();
+            newData.splice(
+              0,
+              4,
+              // @ts-ignore
+              x1 + x2 - item.base[0],
+              // @ts-ignore
+              y1 + y2 - item.base[1],
+            );
+            roundData(newData);
+            const originalLength = cleanupOutData(data, params).length,
+              newLength = cleanupOutData(newData, params).length;
+            if (newLength < originalLength) {
+              command = 'q';
+              data = newData;
+              if (next && next.command == 's') makeLonghand(next, data); // fix up next curve
+            }
+          }
+        }
+      }
+
       // horizontal and vertical line shorthands
       // l 50 0 → h 50
       // l 0 50 → v 50

plugins/plugins-types.d.ts

@@ -41,6 +41,7 @@ type DefaultPlugins = {
       tolerance: number;
     };
     straightCurves?: boolean;
+    convertToQ?: boolean;
     lineShorthands?: boolean;
     convertToZ?: boolean;
     curveSmoothShorthands?: boolean;