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/*
* 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 "SkFixed.h"
#include "SkPathMeasure.h"
#include "SkPointPriv.h"
#include "SkReadBuffer.h"
#include "SkStrokeRec.h"
#include "SkWriteBuffer.h"
sk_sp<SkPathEffect> SkDiscretePathEffect::Make(SkScalar segLength, SkScalar deviation,
uint32_t seedAssist) {
if (!SkScalarIsFinite(segLength) || !SkScalarIsFinite(deviation)) {
return nullptr;
}
if (segLength <= SK_ScalarNearlyZero) {
return nullptr;
}
return sk_sp<SkPathEffect>(new SkDiscretePathEffect(segLength, deviation, seedAssist));
}
static void Perterb(SkPoint* p, const SkVector& tangent, SkScalar scale) {
SkVector normal = tangent;
SkPointPriv::RotateCCW(&normal);
normal.setLength(scale);
*p += normal;
}
SkDiscretePathEffect::SkDiscretePathEffect(SkScalar segLength,
SkScalar deviation,
uint32_t seedAssist)
: fSegLength(segLength), fPerterb(deviation), fSeedAssist(seedAssist)
{
}
/** \class LCGRandom
Utility class that implements pseudo random 32bit numbers using a fast
linear equation. Unlike rand(), this class holds its own seed (initially
set to 0), so that multiple instances can be used with no side-effects.
Copied from the original implementation of SkRandom. Only contains the
methods used by SkDiscretePathEffect::filterPath, with methods that were
not called directly moved to private.
*/
class LCGRandom {
public:
LCGRandom(uint32_t seed) : fSeed(seed) {}
/** Return the next pseudo random number expressed as a SkScalar
in the range [-SK_Scalar1..SK_Scalar1).
*/
SkScalar nextSScalar1() { return SkFixedToScalar(this->nextSFixed1()); }
private:
/** Return the next pseudo random number as an unsigned 32bit value.
*/
uint32_t nextU() { uint32_t r = fSeed * kMul + kAdd; fSeed = r; return r; }
/** Return the next pseudo random number as a signed 32bit value.
*/
int32_t nextS() { return (int32_t)this->nextU(); }
/** Return the next pseudo random number expressed as a signed SkFixed
in the range [-SK_Fixed1..SK_Fixed1).
*/
SkFixed nextSFixed1() { return this->nextS() >> 15; }
// See "Numerical Recipes in C", 1992 page 284 for these constants
enum {
kMul = 1664525,
kAdd = 1013904223
};
uint32_t fSeed;
};
bool SkDiscretePathEffect::filterPath(SkPath* dst, const SkPath& src,
SkStrokeRec* rec, const SkRect*) const {
bool doFill = rec->isFillStyle();
SkPathMeasure meas(src, doFill);
/* Caller may supply their own seed assist, which by default is 0 */
uint32_t seed = fSeedAssist ^ SkScalarRoundToInt(meas.getLength());
LCGRandom 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
} else {
int n = SkScalarRoundToInt(length / fSegLength);
constexpr int kMaxReasonableIterations = 100000;
n = SkTMin(n, kMaxReasonableIterations);
SkScalar delta = length / n;
SkScalar distance = 0;
if (meas.isClosed()) {
n -= 1;
distance += delta/2;
}
if (meas.getPosTan(distance, &p, &v)) {
Perterb(&p, v, rand.nextSScalar1() * scale);
dst->moveTo(p);
}
while (--n >= 0) {
distance += delta;
if (meas.getPosTan(distance, &p, &v)) {
Perterb(&p, v, rand.nextSScalar1() * scale);
dst->lineTo(p);
}
}
if (meas.isClosed()) {
dst->close();
}
}
} while (meas.nextContour());
return true;
}
sk_sp<SkFlattenable> SkDiscretePathEffect::CreateProc(SkReadBuffer& buffer) {
SkScalar segLength = buffer.readScalar();
SkScalar perterb = buffer.readScalar();
uint32_t seed = buffer.readUInt();
return Make(segLength, perterb, seed);
}
void SkDiscretePathEffect::flatten(SkWriteBuffer& buffer) const {
buffer.writeScalar(fSegLength);
buffer.writeScalar(fPerterb);
buffer.writeUInt(fSeedAssist);
}
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