好的，那么问题来了：
我正在制作一个随机生成地形的游戏。地形一次生成并保存到磁盘/SD卡。它做得很好:)
为此，我运行一个 SplashScreenActivity，它运行我的初始启动画面、世界创建或世界加载，具体取决于它的启动方式。实际的程序生成是使用 4D Simplex Noise 使用 Stefan Gustavson 编写并由 Peter Eastman 优化的类完成的（并由我自己优化和加速至少 50%，将变量拉出并使它们成为静态......但问题是我'我即将描述这些变化之前发生的事情）。
基本上我使用他们的噪音功能来填充瓷砖的噪音。在我的世界创建循环中，我循环遍历所有图块，并遍历所有像素，调用类的 SimplexNoise4D.noise(x,y,z,w) 函数来填充每个像素（我计划发送一个 xyzw-per-pixel 集合到该类，以便它可以在该类上运行该方法以更快地访问）。
无论如何，这一切都很好。但是当我退出游戏活动并返回主菜单时，如果我尝试再次运行世界创建，访问 SimplexNoise 类方法（.noise 方法及其使用的内部方法）很慢！！！让调用以正常速度运行的唯一方法是退出整个应用程序（使用任务管理器杀死它）并重新启动应用程序。然后，我第一次运行它时，瓷砖的创建速度就达到了应有的速度。使用调试/方法分析等，似乎对 .noise 方法的调用和对 dot 方法的调用在我第二次尝试运行整个世界创建事物时花费了大量时间。
所以，再次，我第一次循环并使用 SimplexNoise.noise(xyzw) 访问时，它运行良好。然而，第二次访问所有图块中的所有像素（在进入游戏之后），并且对类的所有方法调用都需要永远。
有谁知道为什么会发生这种情况以及如何阻止它发生？
- 编辑 - 只是为了清除问题，应用程序的工作方式如下： mainmenuActivity ->chooseWorldSizeActivity->Splashscreen 通过大量调用 SimplexNoise.noise(xywz)->exit splashscreen->start game Activity 创建世界。
这工作正常且速度快。但是，如果我随后退出 gameActivity（进入主菜单），然后 ->selectWordlSizeActivity->splashscreenActivity，现在对 SimplexNoise.noise(xyzw) 的调用需要永远完成。如果我停止整个应用程序（使用 atskkiller），那么世界创建需要正常时间才能再次运行。我真的不知道为什么！-/编辑-
调用循环（在 ASyncTask 的 doInBackground() 中）就是：
for(loop over rows of tiles)
for(loop over column tiles)
for(each pixel)
create x, y, z, w;
SimplexNoise.noise(xyzw);
单纯形噪声类如下所示：
`
public final class SimplexNoise4D { // Simplex noise in 2D, 3D and 4D
private static final Grad grad3[] = {new Grad(1,1,0),new Grad(-1,1,0),new Grad(1,-1,0),new Grad(-1,-1,0),
new Grad(1,0,1),new Grad(-1,0,1),new Grad(1,0,-1),new Grad(-1,0,-1),
new Grad(0,1,1),new Grad(0,-1,1),new Grad(0,1,-1),new Grad(0,-1,-1)};
private static final Grad grad4[]= {new Grad(0,1,1,1),new Grad(0,1,1,-1),new Grad(0,1,-1,1),new Grad(0,1,-1,-1),
new Grad(0,-1,1,1),new Grad(0,-1,1,-1),new Grad(0,-1,-1,1),new Grad(0,-1,-1,-1),
new Grad(1,0,1,1),new Grad(1,0,1,-1),new Grad(1,0,-1,1),new Grad(1,0,-1,-1),
new Grad(-1,0,1,1),new Grad(-1,0,1,-1),new Grad(-1,0,-1,1),new Grad(-1,0,-1,-1),
new Grad(1,1,0,1),new Grad(1,1,0,-1),new Grad(1,-1,0,1),new Grad(1,-1,0,-1),
new Grad(-1,1,0,1),new Grad(-1,1,0,-1),new Grad(-1,-1,0,1),new Grad(-1,-1,0,-1),
new Grad(1,1,1,0),new Grad(1,1,-1,0),new Grad(1,-1,1,0),new Grad(1,-1,-1,0),
new Grad(-1,1,1,0),new Grad(-1,1,-1,0),new Grad(-1,-1,1,0),new Grad(-1,-1,-1,0)};
private static final short p[] = {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};
// To remove the need for index wrapping, double the permutation table length
private static short perm[] = new short[512];
private static short permMod12[] = new short[512];
static {
for(int i=0; i<512; i++)
{
perm[i]=p[i & 255];
permMod12[i] = (short)(perm[i] % 12);
}
}
// Skewing and unskewing factors for 2, 3, and 4 dimensions
private static final double F2 = 0.5*(Math.sqrt(3.0)-1.0);
private static final double G2 = (3.0-Math.sqrt(3.0))/6.0;
private static final double F3 = 1.0/3.0;
private static final double G3 = 1.0/6.0;
private static final double F4 = (Math.sqrt(5.0)-1.0)/4.0;
private static final double G4 = (5.0-Math.sqrt(5.0))/20.0;
// This method is a *lot* faster than using (int)Math.floor(x)
private static int fastfloor(double x) {
int xi = (int)x;
return x<xi ? xi-1 : xi;
}
private static double dot(Grad g, double x, double y) {
return g.x*x + g.y*y; }
private static double dot(Grad g, double x, double y, double z) {
return g.x*x + g.y*y + g.z*z; }
private static double dot(Grad g, double x, double y, double z, double w) {
return g.x*x + g.y*y + g.z*z + g.w*w; }
private static double n0, n1, n2, n3, n4; // Noise contributions from the five corners
private static double s;// Factor for 4D skewing
private static int i;
private static int j;
private static int k;
private static int l;
private static double t; // Factor for 4D unskewing
private static double X0; // Unskew the cell origin back to (x,y,z,w) space
private static double Y0;
private static double Z0;
private static double W0;
private static double x0; // The x,y,z,w distances from the cell origin
private static double y0;
private static double z0;
private static double w0;
private static int rankx;
private static int ranky;
private static int rankz;
private static int rankw;
private static int i1, j1, k1, l1; // The integer offsets for the second simplex corner
private static int i2, j2, k2, l2; // The integer offsets for the third simplex corner
private static int i3, j3, k3, l3; // The integer offsets for the fourth simplex corner
private static double x1; // Offsets for second corner in (x,y,z,w) coords
private static double y1;
private static double z1;
private static double w1;
private static double x2; // Offsets for third corner in (x,y,z,w) coords
private static double y2;
private static double z2;
private static double w2;
private static double x3; // Offsets for fourth corner in (x,y,z,w) coords
private static double y3;
private static double z3;
private static double w3;
private static double x4; // Offsets for last corner in (x,y,z,w) coords
private static double y4;
private static double z4;
private static double w4;
// Work out the hashed gradient indices of the five simplex corners
private static int ii;
private static int jj;
private static int kk;
private static int ll;
private static int gi0;
private static int gi1;
private static int gi2;
private static int gi3;
private static int gi4;
private static double t0;
private static double t1;
private static double t2;
private static double t3;
private static double t4;
// 4D simplex noise, better simplex rank ordering method 2012-03-09
public static double noise(double x, double y, double z, double w) {
////double n0, n1, n2, n3, n4; // Noise contributions from the five corners
// Skew the (x,y,z,w) space to determine which cell of 24 simplices we're in
////double s = (x + y + z + w) * F4; // Factor for 4D skewing
s = (x + y + z + w) * F4; // Factor for 4D skewing
/*int i = fastfloor(x + s);
int j = fastfloor(y + s);
int k = fastfloor(z + s);
int l = fastfloor(w + s);
double t = (i + j + k + l) * G4; // Factor for 4D unskewing
double X0 = i - t; // Unskew the cell origin back to (x,y,z,w) space
double Y0 = j - t;
double Z0 = k - t;
double W0 = l - t;
double x0 = x - X0; // The x,y,z,w distances from the cell origin
double y0 = y - Y0;
double z0 = z - Z0;
double w0 = w - W0;*/
i = fastfloor(x + s);
j = fastfloor(y + s);
k = fastfloor(z + s);
l = fastfloor(w + s);
t = (i + j + k + l) * G4; // Factor for 4D unskewing
X0 = i - t; // Unskew the cell origin back to (x,y,z,w) space
Y0 = j - t;
Z0 = k - t;
W0 = l - t;
x0 = x - X0; // The x,y,z,w distances from the cell origin
y0 = y - Y0;
z0 = z - Z0;
w0 = w - W0;
// For the 4D case, the simplex is a 4D shape I won't even try to describe.
// To find out which of the 24 possible simplices we're in, we need to
// determine the magnitude ordering of x0, y0, z0 and w0.
// Six pair-wise comparisons are performed between each possible pair
// of the four coordinates, and the results are used to rank the numbers.
/*int rankx = 0;
int ranky = 0;
int rankz = 0;
int rankw = 0;
if(x0 > y0) rankx++; else ranky++;
if(x0 > z0) rankx++; else rankz++;
if(x0 > w0) rankx++; else rankw++;
if(y0 > z0) ranky++; else rankz++;
if(y0 > w0) ranky++; else rankw++;
if(z0 > w0) rankz++; else rankw++;
int i1, j1, k1, l1; // The integer offsets for the second simplex corner
int i2, j2, k2, l2; // The integer offsets for the third simplex corner
int i3, j3, k3, l3; // The integer offsets for the fourth simplex corner*/
rankx = 0;
ranky = 0;
rankz = 0;
rankw = 0;
if(x0 > y0) rankx++; else ranky++;
if(x0 > z0) rankx++; else rankz++;
if(x0 > w0) rankx++; else rankw++;
if(y0 > z0) ranky++; else rankz++;
if(y0 > w0) ranky++; else rankw++;
if(z0 > w0) rankz++; else rankw++;
// simplex[c] is a 4-vector with the numbers 0, 1, 2 and 3 in some order.
// Many values of c will never occur, since e.g. x>y>z>w makes x<z, y<w and x<w
// impossible. Only the 24 indices which have non-zero entries make any sense.
// We use a thresholding to set the coordinates in turn from the largest magnitude.
// Rank 3 denotes the largest coordinate.
i1 = rankx >= 3 ? 1 : 0;
j1 = ranky >= 3 ? 1 : 0;
k1 = rankz >= 3 ? 1 : 0;
l1 = rankw >= 3 ? 1 : 0;
// Rank 2 denotes the second largest coordinate.
i2 = rankx >= 2 ? 1 : 0;
j2 = ranky >= 2 ? 1 : 0;
k2 = rankz >= 2 ? 1 : 0;
l2 = rankw >= 2 ? 1 : 0;
// Rank 1 denotes the second smallest coordinate.
i3 = rankx >= 1 ? 1 : 0;
j3 = ranky >= 1 ? 1 : 0;
k3 = rankz >= 1 ? 1 : 0;
l3 = rankw >= 1 ? 1 : 0;
// The fifth corner has all coordinate offsets = 1, so no need to compute that.
/*double x1 = x0 - i1 + G4; // Offsets for second corner in (x,y,z,w) coords
double y1 = y0 - j1 + G4;
double z1 = z0 - k1 + G4;
double w1 = w0 - l1 + G4;
double x2 = x0 - i2 + 2.0*G4; // Offsets for third corner in (x,y,z,w) coords
double y2 = y0 - j2 + 2.0*G4;
double z2 = z0 - k2 + 2.0*G4;
double w2 = w0 - l2 + 2.0*G4;
double x3 = x0 - i3 + 3.0*G4; // Offsets for fourth corner in (x,y,z,w) coords
double y3 = y0 - j3 + 3.0*G4;
double z3 = z0 - k3 + 3.0*G4;
double w3 = w0 - l3 + 3.0*G4;
double x4 = x0 - 1.0 + 4.0*G4; // Offsets for last corner in (x,y,z,w) coords
double y4 = y0 - 1.0 + 4.0*G4;
double z4 = z0 - 1.0 + 4.0*G4;
double w4 = w0 - 1.0 + 4.0*G4;
// Work out the hashed gradient indices of the five simplex corners
int ii = i & 255;
int jj = j & 255;
int kk = k & 255;
int ll = l & 255;
int gi0 = perm[ii+perm[jj+perm[kk+perm[ll]]]] % 32;
int gi1 = perm[ii+i1+perm[jj+j1+perm[kk+k1+perm[ll+l1]]]] % 32;
int gi2 = perm[ii+i2+perm[jj+j2+perm[kk+k2+perm[ll+l2]]]] % 32;
int gi3 = perm[ii+i3+perm[jj+j3+perm[kk+k3+perm[ll+l3]]]] % 32;
int gi4 = perm[ii+1+perm[jj+1+perm[kk+1+perm[ll+1]]]] % 32;*/
x1 = x0 - i1 + G4; // Offsets for second corner in (x,y,z,w) coords
y1 = y0 - j1 + G4;
z1 = z0 - k1 + G4;
w1 = w0 - l1 + G4;
x2 = x0 - i2 + 2.0*G4; // Offsets for third corner in (x,y,z,w) coords
y2 = y0 - j2 + 2.0*G4;
z2 = z0 - k2 + 2.0*G4;
w2 = w0 - l2 + 2.0*G4;
x3 = x0 - i3 + 3.0*G4; // Offsets for fourth corner in (x,y,z,w) coords
y3 = y0 - j3 + 3.0*G4;
z3 = z0 - k3 + 3.0*G4;
w3 = w0 - l3 + 3.0*G4;
x4 = x0 - 1.0 + 4.0*G4; // Offsets for last corner in (x,y,z,w) coords
y4 = y0 - 1.0 + 4.0*G4;
z4 = z0 - 1.0 + 4.0*G4;
w4 = w0 - 1.0 + 4.0*G4;
// Work out the hashed gradient indices of the five simplex corners
ii = i & 255;
jj = j & 255;
kk = k & 255;
ll = l & 255;
gi0 = perm[ii+perm[jj+perm[kk+perm[ll]]]] % 32;
gi1 = perm[ii+i1+perm[jj+j1+perm[kk+k1+perm[ll+l1]]]] % 32;
gi2 = perm[ii+i2+perm[jj+j2+perm[kk+k2+perm[ll+l2]]]] % 32;
gi3 = perm[ii+i3+perm[jj+j3+perm[kk+k3+perm[ll+l3]]]] % 32;
gi4 = perm[ii+1+perm[jj+1+perm[kk+1+perm[ll+1]]]] % 32;
// Calculate the contribution from the five corners
/*double t0 = 0.6 - x0*x0 - y0*y0 - z0*z0 - w0*w0;
if(t0<0) n0 = 0.0;
else {
t0 *= t0;
n0 = t0 * t0 * dot(grad4[gi0], x0, y0, z0, w0);
}
double t1 = 0.6 - x1*x1 - y1*y1 - z1*z1 - w1*w1;
if(t1<0) n1 = 0.0;
else {
t1 *= t1;
n1 = t1 * t1 * dot(grad4[gi1], x1, y1, z1, w1);
}
double t2 = 0.6 - x2*x2 - y2*y2 - z2*z2 - w2*w2;
if(t2<0) n2 = 0.0;
else {
t2 *= t2;
n2 = t2 * t2 * dot(grad4[gi2], x2, y2, z2, w2);
}
double t3 = 0.6 - x3*x3 - y3*y3 - z3*z3 - w3*w3;
if(t3<0) n3 = 0.0;
else {
t3 *= t3;
n3 = t3 * t3 * dot(grad4[gi3], x3, y3, z3, w3);
}
double t4 = 0.6 - x4*x4 - y4*y4 - z4*z4 - w4*w4;
if(t4<0) n4 = 0.0;
else {
t4 *= t4;
n4 = t4 * t4 * dot(grad4[gi4], x4, y4, z4, w4);
}*/
t0 = 0.6 - x0*x0 - y0*y0 - z0*z0 - w0*w0;
if(t0<0) n0 = 0.0;
else {
t0 *= t0;
n0 = t0 * t0 * dot(grad4[gi0], x0, y0, z0, w0);
}
t1 = 0.6 - x1*x1 - y1*y1 - z1*z1 - w1*w1;
if(t1<0) n1 = 0.0;
else {
t1 *= t1;
n1 = t1 * t1 * dot(grad4[gi1], x1, y1, z1, w1);
}
t2 = 0.6 - x2*x2 - y2*y2 - z2*z2 - w2*w2;
if(t2<0) n2 = 0.0;
else {
t2 *= t2;
n2 = t2 * t2 * dot(grad4[gi2], x2, y2, z2, w2);
}
t3 = 0.6 - x3*x3 - y3*y3 - z3*z3 - w3*w3;
if(t3<0) n3 = 0.0;
else {
t3 *= t3;
n3 = t3 * t3 * dot(grad4[gi3], x3, y3, z3, w3);
}
t4 = 0.6 - x4*x4 - y4*y4 - z4*z4 - w4*w4;
if(t4<0) n4 = 0.0;
else {
t4 *= t4;
n4 = t4 * t4 * dot(grad4[gi4], x4, y4, z4, w4);
}
// Sum up and scale the result to cover the range [-1,1]
return 27.0 * (n0 + n1 + n2 + n3 + n4);
}
// Inner class to speed up gradient computations
// (array access is a lot slower than member access)
private static class Grad
{
double x, y, z, w;
Grad(double x, double y, double z)
{
this.x = x;
this.y = y;
this.z = z;
}
Grad(double x, double y, double z, double w)
{
this.x = x;
this.y = y;
this.z = z;
this.w = w;
}
}
}
`