Eryn Wells
11b9cba8ac
This object contains several random numbers for the GPU kernel to use when generating random points. This isn't right yet (there are still patterns in the generated data) but it's time to move on...
62 lines
1.8 KiB
Metal
62 lines
1.8 KiB
Metal
//
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// TerrainAlgorithms.metal
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// Terrain2
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//
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// Created by Eryn Wells on 11/4/18.
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// Copyright © 2018 Eryn Wells. All rights reserved.
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//
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#include <metal_stdlib>
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#include <metal_types>
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#include "ShaderTypes.h"
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using namespace metal;
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/// A pseudo-random number generator providing several algorithms.
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/// - http://reedbeta.com/blog/quick-and-easy-gpu-random-numbers-in-d3d11/
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struct PRNG {
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PRNG(uint seed) : mSeed(wangHash(seed)) { }
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/// Generate a random unsigned integer using a linear congruential generator.
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uint lcg() {
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mSeed = 1664525 * mSeed + 1013904223;
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return mSeed;
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}
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/// Generate a random unsigned integer using the Xorshift algorithm from George Marsaglia's paper.
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uint xorShift() {
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mSeed ^= (mSeed << 13);
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mSeed ^= (mSeed >> 17);
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mSeed ^= (mSeed << 5);
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return mSeed;
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}
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uint wangHash(uint seed) {
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seed = (seed ^ 61) ^ (seed >> 16);
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seed *= 9;
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seed = seed ^ (seed >> 4);
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seed *= 0x27d4eb2d;
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seed = seed ^ (seed >> 15);
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return seed;
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}
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private:
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uint mSeed;
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};
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kernel void zeroKernel(texture2d<float, access::write> outTexture [[texture(GeneratorTextureIndexOut)]],
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uint2 tid [[thread_position_in_grid]])
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{
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outTexture.write(0, tid);
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}
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#pragma mark - RandomAlgorithm
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kernel void randomKernel(texture2d<float, access::write> outTexture [[texture(GeneratorTextureIndexOut)]],
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constant RandomAlgorithmUniforms &uniforms [[buffer(0)]],
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uint2 tid [[thread_position_in_grid]])
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{
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PRNG rng(uniforms.randoms[(tid.x * tid.y) % kRandomAlgorithmUniforms_RandomCount]);
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uint r = rng.xorShift();
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float x = float(r * (1.0 / float(UINT_MAX))) * 0.5f;
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outTexture.write(x, tid);
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}
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