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Generate some pseudo-random numbers with a PRNG class in the shaders.

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This commit is contained in:
Eryn Wells 2018-11-04 22:30:06 -05:00
parent bd9cba2886
commit 76f0065d8b
1 changed files with 39 additions and 3 deletions
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42
Terrain2/TerrainAlgorithms.metal
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@ -7,9 +7,42 @@
//
#include <metal_stdlib>
#include <metal_types>
#include "ShaderTypes.h"
using namespace metal;
/// A pseudo-random number generator providing several algorithms.
/// - http://reedbeta.com/blog/quick-and-easy-gpu-random-numbers-in-d3d11/
struct PRNG {
PRNG(uint seed) : mSeed(wangHash(seed)) { }
/// Generate a random unsigned integer using a linear congruential generator.
uint lcg() {
mSeed = 1664525 * mSeed + 1013904223;
return mSeed;
}
/// Generate a random unsigned integer using the Xorshift algorithm from George Marsaglia's paper.
uint xorShift() {
mSeed ^= (mSeed << 13);
mSeed ^= (mSeed >> 17);
mSeed ^= (mSeed << 5);
return mSeed;
}
uint wangHash(uint seed) {
seed = (seed ^ 61) ^ (seed >> 16);
seed *= 9;
seed = seed ^ (seed >> 4);
seed *= 0x27d4eb2d;
seed = seed ^ (seed >> 15);
return seed;
}
private:
uint mSeed;
};
kernel void zeroKernel(texture2d<float, access::write> outTexture [[texture(GeneratorTextureIndexOut)]],
uint2 tid [[thread_position_in_grid]])
{
@ -17,8 +50,11 @@ kernel void zeroKernel(texture2d<float, access::write> outTexture [[texture(Gene
}
kernel void randomKernel(texture2d<float, access::write> outTexture [[texture(GeneratorTextureIndexOut)]],
uint2 tid [[thread_position_in_grid]])
uint2 tid [[thread_position_in_grid]],
uint2 tgid [[threadgroup_position_in_grid]])
{
float x = 2.0 * M_PI_F * (tid.x / 128.0);
outTexture.write(sin(x), tid);
PRNG rng(tid.x * tid.y);
uint r = rng.lcg();
float x = float(r * (1.0 / float(UINT_MAX))) * 0.5f;
outTexture.write(x, tid);
}