aboutsummaryrefslogtreecommitdiffhomepage
path: root/src/effects/SkDiscretePathEffect.cpp
blob: 4525c1e32ab06669bef79858acf7c2dbabd0b92e (plain)
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
/*
 * 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 "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;
    normal.rotateCCW();
    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);
            SkScalar    delta = length / n;
            SkScalar    distance = 0;

            if (meas.isClosed()) {
                n -= 1;
                distance += delta/2;
            }

            if (meas.getPosTan(distance, &p, &v)) {
                Perterb(&p, v, SkScalarMul(rand.nextSScalar1(), scale));
                dst->moveTo(p);
            }
            while (--n >= 0) {
                distance += delta;
                if (meas.getPosTan(distance, &p, &v)) {
                    Perterb(&p, v, SkScalarMul(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);
}

#ifndef SK_IGNORE_TO_STRING
void SkDiscretePathEffect::toString(SkString* str) const {
    str->appendf("SkDiscretePathEffect: (");
    str->appendf("segLength: %.2f deviation: %.2f seed %d", fSegLength, fPerterb, fSeedAssist);
    str->append(")");
}
#endif