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Switch to Skia raster context if Skia GPU context is not available
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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. | ||
*/ | ||
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#ifndef SkRandom_DEFINED | ||
#define SkRandom_DEFINED | ||
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#include "include/core/SkScalar.h" | ||
#include "include/private/SkFixed.h" | ||
#include "include/private/SkFloatBits.h" | ||
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/** \class SkRandom | ||
Utility class that implements pseudo random 32bit numbers using Marsaglia's | ||
multiply-with-carry "mother of all" algorithm. Unlike rand(), this class holds | ||
its own state, so that multiple instances can be used with no side-effects. | ||
Has a large period and all bits are well-randomized. | ||
*/ | ||
class SkRandom { | ||
public: | ||
SkRandom() { init(0); } | ||
SkRandom(uint32_t seed) { init(seed); } | ||
SkRandom(const SkRandom& rand) : fK(rand.fK), fJ(rand.fJ) {} | ||
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SkRandom& operator=(const SkRandom& rand) { | ||
fK = rand.fK; | ||
fJ = rand.fJ; | ||
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return *this; | ||
} | ||
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/** Return the next pseudo random number as an unsigned 32bit value. | ||
*/ | ||
uint32_t nextU() { | ||
fK = kKMul*(fK & 0xffff) + (fK >> 16); | ||
fJ = kJMul*(fJ & 0xffff) + (fJ >> 16); | ||
return (((fK << 16) | (fK >> 16)) + fJ); | ||
} | ||
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/** Return the next pseudo random number as a signed 32bit value. | ||
*/ | ||
int32_t nextS() { return (int32_t)this->nextU(); } | ||
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/** | ||
* Returns value [0...1) as an IEEE float | ||
*/ | ||
float nextF() { | ||
int floatint = 0x3f800000 | (int)(this->nextU() >> 9); | ||
float f = SkBits2Float(floatint) - 1.0f; | ||
return f; | ||
} | ||
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/** | ||
* Returns value [min...max) as a float | ||
*/ | ||
float nextRangeF(float min, float max) { | ||
return min + this->nextF() * (max - min); | ||
} | ||
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/** Return the next pseudo random number, as an unsigned value of | ||
at most bitCount bits. | ||
@param bitCount The maximum number of bits to be returned | ||
*/ | ||
uint32_t nextBits(unsigned bitCount) { | ||
SkASSERT(bitCount > 0 && bitCount <= 32); | ||
return this->nextU() >> (32 - bitCount); | ||
} | ||
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/** Return the next pseudo random unsigned number, mapped to lie within | ||
[min, max] inclusive. | ||
*/ | ||
uint32_t nextRangeU(uint32_t min, uint32_t max) { | ||
SkASSERT(min <= max); | ||
uint32_t range = max - min + 1; | ||
if (0 == range) { | ||
return this->nextU(); | ||
} else { | ||
return min + this->nextU() % range; | ||
} | ||
} | ||
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/** Return the next pseudo random unsigned number, mapped to lie within | ||
[0, count). | ||
*/ | ||
uint32_t nextULessThan(uint32_t count) { | ||
SkASSERT(count > 0); | ||
return this->nextRangeU(0, count - 1); | ||
} | ||
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/** Return the next pseudo random number expressed as a SkScalar | ||
in the range [0..SK_Scalar1). | ||
*/ | ||
SkScalar nextUScalar1() { return SkFixedToScalar(this->nextUFixed1()); } | ||
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/** Return the next pseudo random number expressed as a SkScalar | ||
in the range [min..max). | ||
*/ | ||
SkScalar nextRangeScalar(SkScalar min, SkScalar max) { | ||
return this->nextUScalar1() * (max - min) + min; | ||
} | ||
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/** Return the next pseudo random number expressed as a SkScalar | ||
in the range [-SK_Scalar1..SK_Scalar1). | ||
*/ | ||
SkScalar nextSScalar1() { return SkFixedToScalar(this->nextSFixed1()); } | ||
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/** Return the next pseudo random number as a bool. | ||
*/ | ||
bool nextBool() { return this->nextU() >= 0x80000000; } | ||
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/** A biased version of nextBool(). | ||
*/ | ||
bool nextBiasedBool(SkScalar fractionTrue) { | ||
SkASSERT(fractionTrue >= 0 && fractionTrue <= SK_Scalar1); | ||
return this->nextUScalar1() <= fractionTrue; | ||
} | ||
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/** Reset the random object. | ||
*/ | ||
void setSeed(uint32_t seed) { init(seed); } | ||
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private: | ||
// Initialize state variables with LCG. | ||
// We must ensure that both J and K are non-zero, otherwise the | ||
// multiply-with-carry step will forevermore return zero. | ||
void init(uint32_t seed) { | ||
fK = NextLCG(seed); | ||
if (0 == fK) { | ||
fK = NextLCG(fK); | ||
} | ||
fJ = NextLCG(fK); | ||
if (0 == fJ) { | ||
fJ = NextLCG(fJ); | ||
} | ||
SkASSERT(0 != fK && 0 != fJ); | ||
} | ||
static uint32_t NextLCG(uint32_t seed) { return kMul*seed + kAdd; } | ||
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/** Return the next pseudo random number expressed as an unsigned SkFixed | ||
in the range [0..SK_Fixed1). | ||
*/ | ||
SkFixed nextUFixed1() { return this->nextU() >> 16; } | ||
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/** Return the next pseudo random number expressed as a signed SkFixed | ||
in the range [-SK_Fixed1..SK_Fixed1). | ||
*/ | ||
SkFixed nextSFixed1() { return this->nextS() >> 15; } | ||
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// See "Numerical Recipes in C", 1992 page 284 for these constants | ||
// For the LCG that sets the initial state from a seed | ||
enum { | ||
kMul = 1664525, | ||
kAdd = 1013904223 | ||
}; | ||
// Constants for the multiply-with-carry steps | ||
enum { | ||
kKMul = 30345, | ||
kJMul = 18000, | ||
}; | ||
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uint32_t fK; | ||
uint32_t fJ; | ||
}; | ||
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#endif |
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