【发布时间】：2018-01-04 01:47:38
【问题描述】：
所以，我一直在尝试在我的项目中使用 Perlin Noise，但奇怪的是，噪声函数输出的值大多超出 [-1, 1] 范围。我已经通过Perlin's code for his improved noise in Java 和another useful implementation in C++ by sol 在C 中实现了它。我已经运行了至少 20 次并确保它完全一样，但找不到任何问题的原因。 这是它的外观：
// DEFAULT_PERMUTATION is defined through the preprocessor.
// It is basically an initializer of the same array used in Perlin's
// implementation, except it has been duplicated into a 512 element array
double simpleNoise(double x, double y, double z){
double res;
int p[512] = DEFAULT_PERMUTATION;
int X = (int) floor(x) & 255;
int Y = (int) floor(y) & 255;
int Z = (int) floor(z) & 255;
double u = fade(x);
double v = fade(y);
double w = fade(z);
int A = p[X] + Y;
int AA = p[A] + Z;
int AB = p[A + 1] + Z;
int B = p[X + 1] + Y;
int BA = p[B] + Z;
int BB = p[B + 1] + Z;
x -= floor(x);
y -= floor(y);
z -= floor(z);
res = lerp(w, lerp(v, lerp(u, grad(p[AA ], x , y , z ),
grad(p[BA ], x-1, y , z )),
lerp(u, grad(p[AB ], x , y-1, z ),
grad(p[BB ], x-1, y-1, z ))),
lerp(v, lerp(u, grad(p[AA+1], x , y , z-1 ),
grad(p[BA+1], x-1, y , z-1 )),
lerp(u, grad(p[AB+1], x , y-1, z-1 ),
grad(p[BB+1], x-1, y-1, z-1 ))));
return res;
}
其他私有函数也很简单：
double fade(double t){
return t * t * t * (t * (t * 6 - 15) + 10);
}
double lerp(double t, double a, double b){
return a + t * (b - a);
}
double grad(int hash, double x, double y, double z){
int h = hash & 15;
double u = h<8 ? x : y,
v = h<4 ? y : h==12||h==14 ? x : z;
return ((h&1) == 0 ? u : -u) + ((h&2) == 0 ? v : -v);
}
In my project, the noise looks like this，因为颜色只关心 0 到 1 之间的值，但对某些位置的测试会给出荒谬的值，例如 -15、32，有些大于数千。输入值 (1,-4,1), (2,5,1), (2,0,0) 至少可以说很有趣。
可能是什么问题？
编辑：出于调查目的，此程序列出了发现的不一致之处：
#define DEFAULT_PERMUTATION { \
151,160,137,91,90,15,131,13,201,95,96,53,194,233,7,225,140,36,103,30,69,142, \
8,99,37,240,21,10,23,190, 6,148,247,120,234,75,0,26,197,62,94,252,219,203,117, \
35,11,32,57,177,33,88,237,149,56,87,174,20,125,136,171,168, 68,175,74,165,71, \
134,139,48,27,166,77,146,158,231,83,111,229,122,60,211,133,230,220,105,92,41, \
55,46,245,40,244,102,143,54, 65,25,63,161,1,216,80,73,209,76,132,187,208, 89, \
18,169,200,196,135,130,116,188,159,86,164,100,109,198,173,186, 3,64,52,217,226, \
250,124,123,5,202,38,147,118,126,255,82,85,212,207,206,59,227,47,16,58,17,182, \
189,28,42,223,183,170,213,119,248,152, 2,44,154,163, 70,221,153,101,155,167, \
43,172,9,129,22,39,253, 19,98,108,110,79,113,224,232,178,185, 112,104,218,246, \
97,228,251,34,242,193,238,210,144,12,191,179,162,241, 81,51,145,235,249,14,239, \
107,49,192,214, 31,181,199,106,157,184, 84,204,176,115,121,50,45,127, 4,150,254, \
138,236,205,93,222,114,67,29,24,72,243,141,128,195,78,66,215,61,156,180,\
151,160,137,91,90,15,131,13,201,95,96,53,194,233,7,225,140,36,103,30,69,142, \
8,99,37,240,21,10,23,190, 6,148,247,120,234,75,0,26,197,62,94,252,219,203,117, \
35,11,32,57,177,33,88,237,149,56,87,174,20,125,136,171,168, 68,175,74,165,71, \
134,139,48,27,166,77,146,158,231,83,111,229,122,60,211,133,230,220,105,92,41, \
55,46,245,40,244,102,143,54, 65,25,63,161,1,216,80,73,209,76,132,187,208, 89, \
18,169,200,196,135,130,116,188,159,86,164,100,109,198,173,186, 3,64,52,217,226, \
250,124,123,5,202,38,147,118,126,255,82,85,212,207,206,59,227,47,16,58,17,182, \
189,28,42,223,183,170,213,119,248,152, 2,44,154,163, 70,221,153,101,155,167, \
43,172,9,129,22,39,253, 19,98,108,110,79,113,224,232,178,185, 112,104,218,246, \
97,228,251,34,242,193,238,210,144,12,191,179,162,241, 81,51,145,235,249,14,239, \
107,49,192,214, 31,181,199,106,157,184, 84,204,176,115,121,50,45,127, 4,150,254, \
138,236,205,93,222,114,67,29,24,72,243,141,128,195,78,66,215,61,156,180 }
#define SIZE 10
double fade(double t){
return t * t * t * (t * (t * 6 - 15) + 10);
}
double lerp(double t, double a, double b){
return a + t * (b - a);
}
double grad(int hash, double x, double y, double z){
int h = hash & 15;
double u = h<8 ? x : y,
v = h<4 ? y : h==12||h==14 ? x : z;
return ((h&1) == 0 ? u : -u) + ((h&2) == 0 ? v : -v);
}
double simpleNoise(double x, double y, double z){
double res;
int p[512] = DEFAULT_PERMUTATION;
int X = (int) floor(x) & 255;
int Y = (int) floor(y) & 255;
int Z = (int) floor(z) & 255;
double u = fade(x);
double v = fade(y);
double w = fade(z);
int A = p[X] + Y;
int AA = p[A] + Z;
int AB = p[A + 1] + Z;
int B = p[X + 1] + Y;
int BA = p[B] + Z;
int BB = p[B + 1] + Z;
x -= floor(x);
y -= floor(y);
z -= floor(z);
res = lerp(w, lerp(v, lerp(u, grad(p[AA ], x , y , z ),
grad(p[BA ], x-1, y , z )),
lerp(u, grad(p[AB ], x , y-1, z ),
grad(p[BB ], x-1, y-1, z ))),
lerp(v, lerp(u, grad(p[AA+1], x , y , z-1 ),
grad(p[BA+1], x-1, y , z-1 )),
lerp(u, grad(p[AB+1], x , y-1, z-1 ),
grad(p[BB+1], x-1, y-1, z-1 ))));
return res;
}
main(){
int i, j, k, n=0;
double e;
for(i=-SIZE/2; i<SIZE/2; i++){
for(j=-SIZE/2; j<SIZE/2; j++){
for(k=-SIZE/2; k<SIZE/2; k++){
e = simpleNoise(i, j, k);
if(fabs(e) > 1){
printf("P(%d,%d,%d): %f\n", i, j, k, e);
n++;
}
}
}
}
printf("%d inconsistencies found", n);
}
【问题讨论】：
-
我认为我们需要有一个minimal reproducible example，因为它没有像显示的那样运行，我们需要检查你的函数的结果。
-
添加了一个代码，可以测试第 10 面框中点的函数。在 1000 个点中，966 个是荒谬的。
-
贴出的代码无法编译！请发布minimal reproducible example，以便我们重现问题。
-
为了便于阅读和理解：1) 一致地缩进代码。在每个左大括号 '{' 后缩进。在每个右大括号 '}' 之前不缩进。建议每个缩进级别为 4 个空格。 2) 通过一个空行分隔代码块（for、if、else、while、do...while、switch、case、default）。 3) 用 2 或 3 个空行分隔函数（保持一致）
-
参数和变量名称应指示
content或usage（或更好，两者兼有）。 't', 'a', 'b', 'x', 'y', 'z', 'h', 'u', 'v', 'p', 'BA', 'AA', 'BB'、'AB' 等是没有意义的，即使在当前上下文中也是如此
标签： c opengl noise perlin-noise