Optimize save-transform-constructPath-restore

The 4 operations can be replaced with just one in applying the transform to the points coordinates.

src/core/operator_list.js

@@ -13,7 +13,14 @@
  * limitations under the License.
  */
 
-import { ImageKind, OPS, RenderingIntentFlag, warn } from "../shared/util.js";
+import {
+  DrawOPS,
+  ImageKind,
+  OPS,
+  RenderingIntentFlag,
+  Util,
+  warn,
+} from "../shared/util.js";
 
 function addState(parentState, pattern, checkFn, iterateFn, processFn) {
   let state = parentState;
@@ -470,6 +477,70 @@ addState(
   }
 );
 
+// This replaces (save, transform, constructPath, restore)
+// sequences with |constructPath| operation.
+addState(
+  InitialState,
+  [OPS.save, OPS.transform, OPS.constructPath, OPS.restore],
+  context => {
+    const argsArray = context.argsArray;
+    const iFirstConstructPath = context.iCurr - 1;
+    const op = argsArray[iFirstConstructPath][0];
+
+    // When stroking the transform has to be applied to the line width too.
+    // So we can only optimize if the transform is an identity.
+    if (
+      op !== OPS.stroke &&
+      op !== OPS.closeStroke &&
+      op !== OPS.fillStroke &&
+      op !== OPS.eoFillStroke &&
+      op !== OPS.closeFillStroke &&
+      op !== OPS.closeEOFillStroke
+    ) {
+      return true;
+    }
+    const iFirstTransform = context.iCurr - 2;
+    const transform = argsArray[iFirstTransform];
+    return (
+      transform[0] === 1 &&
+      transform[1] === 0 &&
+      transform[2] === 0 &&
+      transform[3] === 1
+    );
+  },
+  () => false,
+  (context, i) => {
+    const { fnArray, argsArray } = context;
+    const curr = context.iCurr;
+    const iFirstSave = curr - 3;
+    const iFirstTransform = curr - 2;
+    const iFirstConstructPath = curr - 1;
+    const args = argsArray[iFirstConstructPath];
+    const transform = argsArray[iFirstTransform];
+    const [, [buffer], minMax] = args;
+
+    Util.scaleMinMax(transform, minMax);
+    for (let k = 0, kk = buffer.length; k < kk; ) {
+      switch (buffer[k++]) {
+        case DrawOPS.moveTo:
+        case DrawOPS.lineTo:
+          Util.applyTransformInPlace(buffer.subarray(k), transform);
+          k += 2;
+          break;
+        case DrawOPS.curveTo:
+          Util.applyTransformToBezierInPlace(buffer.subarray(k), transform);
+          k += 6;
+          break;
+      }
+    }
+    // Replace queue items.
+    fnArray.splice(iFirstSave, 4, OPS.constructPath);
+    argsArray.splice(iFirstSave, 4, args);
+
+    return iFirstSave + 1;
+  }
+);
+
 class NullOptimizer {
   constructor(queue) {
     this.queue = queue;

src/shared/util.js

@@ -676,6 +676,57 @@ class Util {
     return `#${hexNumbers[r]}${hexNumbers[g]}${hexNumbers[b]}`;
   }
 
+  // Apply a scaling matrix to some min/max values.
+  // If a scaling factor is negative then min and max must be
+  // swapped.
+  static scaleMinMax(transform, minMax) {
+    let temp;
+    if (transform[0]) {
+      if (transform[0] < 0) {
+        temp = minMax[0];
+        minMax[0] = minMax[2];
+        minMax[2] = temp;
+      }
+      minMax[0] *= transform[0];
+      minMax[2] *= transform[0];
+
+      if (transform[3] < 0) {
+        temp = minMax[1];
+        minMax[1] = minMax[3];
+        minMax[3] = temp;
+      }
+      minMax[1] *= transform[3];
+      minMax[3] *= transform[3];
+    } else {
+      temp = minMax[0];
+      minMax[0] = minMax[1];
+      minMax[1] = temp;
+      temp = minMax[2];
+      minMax[2] = minMax[3];
+      minMax[3] = temp;
+
+      if (transform[1] < 0) {
+        temp = minMax[1];
+        minMax[1] = minMax[3];
+        minMax[3] = temp;
+      }
+      minMax[1] *= transform[1];
+      minMax[3] *= transform[1];
+
+      if (transform[2] < 0) {
+        temp = minMax[0];
+        minMax[0] = minMax[2];
+        minMax[2] = temp;
+      }
+      minMax[0] *= transform[2];
+      minMax[2] *= transform[2];
+    }
+    minMax[0] += transform[4];
+    minMax[1] += transform[5];
+    minMax[2] += transform[4];
+    minMax[3] += transform[5];
+  }
+
   // Concatenates two transformation matrices together and returns the result.
   static transform(m1, m2) {
     return [
@@ -695,6 +746,22 @@ class Util {
     return [xt, yt];
   }
 
+  static applyTransformInPlace(p, m) {
+    const [p0, p1] = p;
+    p[0] = p0 * m[0] + p1 * m[2] + m[4];
+    p[1] = p0 * m[1] + p1 * m[3] + m[5];
+  }
+
+  // For 2d affine transforms
+  static applyTransformToBezierInPlace(p, [m0, m1, m2, m3, m4, m5]) {
+    for (let i = 0; i < 6; i += 2) {
+      const pI = p[i];
+      const pI1 = p[i + 1];
+      p[i] = pI * m0 + pI1 * m2 + m4;
+      p[i + 1] = pI * m1 + pI1 * m3 + m5;
+    }
+  }
+
   static applyInverseTransform(p, m) {
     const d = m[0] * m[3] - m[1] * m[2];
     const xt = (p[0] * m[3] - p[1] * m[2] + m[2] * m[5] - m[4] * m[3]) / d;