Randomize seed for SkDiscretePathEffect::filterPath()

src/effects/SkDiscretePathEffect.cpp

 
 /*
  * Copyright 2006 The Android Open Source Project
  *
  * Use of this source code is governed by a BSD-style license that can be
  * found in the LICENSE file.
  */
 
 
 #include "SkDiscretePathEffect.h"
 #include "SkReadBuffer.h"
 #include "SkWriteBuffer.h"
 #include "SkPathMeasure.h"
 #include "SkRandom.h"
 
 static void Perterb(SkPoint* p, const SkVector& tangent, SkScalar scale) {
     SkVector normal = tangent;
     normal.rotateCCW();
     normal.setLength(scale);
     *p += normal;
 }
 
-
-SkDiscretePathEffect::SkDiscretePathEffect(SkScalar segLength, SkScalar deviation)
-    : fSegLength(segLength), fPerterb(deviation)
+SkDiscretePathEffect::SkDiscretePathEffect(SkScalar segLength,
+                                           SkScalar deviation,
+                                           uint32_t seedAssist)
+    : fSegLength(segLength), fPerterb(deviation), fSeedAssist(seedAssist)
 {
 }
 
 bool SkDiscretePathEffect::filterPath(SkPath* dst, const SkPath& src,
                                       SkStrokeRec* rec, const SkRect*) const {
     bool doFill = rec->isFillStyle();
 
     SkPathMeasure   meas(src, doFill);
-    uint32_t        seed = SkScalarRoundToInt(meas.getLength());
+
+    /* Caller may supply their own seed assist, which by default is 0 */
+    uint32_t seed = fSeedAssist ^ SkScalarRoundToInt(meas.getLength());
+
     SkLCGRandom     rand(seed ^ ((seed << 16) | (seed >> 16)));
     SkScalar        scale = fPerterb;
     SkPoint         p;
     SkVector        v;
 
     do {
         SkScalar    length = meas.getLength();
 
         if (fSegLength * (2 + doFill) > length) {
             meas.getSegment(0, length, dst, true);  // to short for us to mangle
@@ skipping 23 matching lines @@
             }
         }
     } while (meas.nextContour());
     return true;
 }
 
 void SkDiscretePathEffect::flatten(SkWriteBuffer& buffer) const {
     this->INHERITED::flatten(buffer);
     buffer.writeScalar(fSegLength);
     buffer.writeScalar(fPerterb);
+    buffer.writeUInt(fSeedAssist);
 }
 
 SkDiscretePathEffect::SkDiscretePathEffect(SkReadBuffer& buffer) {
     fSegLength = buffer.readScalar();
     fPerterb = buffer.readScalar();
+    fSeedAssist = buffer.readUInt();
 }