Perlin噪音在某些设备（Android，GLSL）上有问题

Question

我正在为Android开发OpenGLES应用程序，并使用Stefan Gustavson的Perlin噪声。 它是2D动画动画，因此我将3D Perlin与时间变量作为第三维。 在我的Samsung Galaxy Young（API 10）上一切看起来都不错，但是当我用ASUS MEMO平板电脑（API 17）测试它时，我得到了即使在椭圆形或类似正方形区域的故障信号：-

是什么导致各种设备之间的这种差异？

片段着色器代码：

precision mediump float;
varying vec2 screenPosition;
uniform vec4 colorFilter;
uniform float time;

vec4 permute(vec4 x)
{
  return mod(((x*34.0)+1.0)*x, 289.0);
}

vec4 taylorInvSqrt(vec4 r)
{
  return 1.79284291400159 - 0.85373472095314 * r;
}

vec3 fade(vec3 t) {
  return t*t*t*(t*(t*6.0-15.0)+10.0);
}

float noise(vec3 P)
{
  vec3 Pi0 = floor(P); // Integer part for indexing
  vec3 Pi1 = Pi0 + vec3(1.0); // Integer part + 1
  Pi0 = mod(Pi0, 289.0);
  Pi1 = mod(Pi1, 289.0);
  vec3 Pf0 = fract(P); // Fractional part for interpolation
  vec3 Pf1 = Pf0 - vec3(1.0); // Fractional part - 1.0
  vec4 ix = vec4(Pi0.x, Pi1.x, Pi0.x, Pi1.x);
  vec4 iy = vec4(Pi0.yy, Pi1.yy);
  vec4 iz0 = Pi0.zzzz;
  vec4 iz1 = Pi1.zzzz;

  vec4 ixy = permute(permute(ix) + iy);
  vec4 ixy0 = permute(ixy + iz0);
  vec4 ixy1 = permute(ixy + iz1);

  vec4 gx0 = ixy0 / 7.0;
  vec4 gy0 = fract(floor(gx0) / 7.0) - 0.5;
  gx0 = fract(gx0);
  vec4 gz0 = vec4(0.5) - abs(gx0) - abs(gy0);
  vec4 sz0 = step(gz0, vec4(0.0));
  gx0 -= sz0 * (step(0.0, gx0) - 0.5);
  gy0 -= sz0 * (step(0.0, gy0) - 0.5);

  vec4 gx1 = ixy1 / 7.0;
  vec4 gy1 = fract(floor(gx1) / 7.0) - 0.5;
  gx1 = fract(gx1);
  vec4 gz1 = vec4(0.5) - abs(gx1) - abs(gy1);
  vec4 sz1 = step(gz1, vec4(0.0));
  gx1 -= sz1 * (step(0.0, gx1) - 0.5);
  gy1 -= sz1 * (step(0.0, gy1) - 0.5);

  vec3 g000 = vec3(gx0.x,gy0.x,gz0.x);
  vec3 g100 = vec3(gx0.y,gy0.y,gz0.y);
  vec3 g010 = vec3(gx0.z,gy0.z,gz0.z);
  vec3 g110 = vec3(gx0.w,gy0.w,gz0.w);
  vec3 g001 = vec3(gx1.x,gy1.x,gz1.x);
  vec3 g101 = vec3(gx1.y,gy1.y,gz1.y);
  vec3 g011 = vec3(gx1.z,gy1.z,gz1.z);
  vec3 g111 = vec3(gx1.w,gy1.w,gz1.w);

  vec4 norm0 = taylorInvSqrt(vec4(dot(g000, g000), dot(g010, g010), dot(g100, g100), dot(g110, g110)));
  g000 *= norm0.x;
  g010 *= norm0.y;
  g100 *= norm0.z;
  g110 *= norm0.w;
  vec4 norm1 = taylorInvSqrt(vec4(dot(g001, g001), dot(g011, g011), dot(g101, g101), dot(g111, g111)));
  g001 *= norm1.x;
  g011 *= norm1.y;
  g101 *= norm1.z;
  g111 *= norm1.w;

  float n000 = dot(g000, Pf0);
  float n100 = dot(g100, vec3(Pf1.x, Pf0.yz));
  float n010 = dot(g010, vec3(Pf0.x, Pf1.y, Pf0.z));
  float n110 = dot(g110, vec3(Pf1.xy, Pf0.z));
  float n001 = dot(g001, vec3(Pf0.xy, Pf1.z));
  float n101 = dot(g101, vec3(Pf1.x, Pf0.y, Pf1.z));
  float n011 = dot(g011, vec3(Pf0.x, Pf1.yz));
  float n111 = dot(g111, Pf1);

  vec3 fade_xyz = fade(Pf0);
  vec4 n_z = mix(vec4(n000, n100, n010, n110), vec4(n001, n101, n011, n111), fade_xyz.z);
  vec2 n_yz = mix(n_z.xy, n_z.zw, fade_xyz.y);
  float n_xyz = mix(n_yz.x, n_yz.y, fade_xyz.x); 
  return 2.2 * n_xyz;
}

void main() {
    float valuer = (noise(vec3(screenPosition.x*4.0, screenPosition.y*3.0, time)));
    float val1 = 0.25*(sign(valuer+0.2)-sign(valuer-0.2));
    float val2 = 0.125*(sign(valuer+0.4)-sign(valuer-0.4));
    outputColor = colorFilter*(val1+val2+0.25);
}

Answer 1

三星Galaxy Young最有可能以较高的速度执行数学运算，而ASUS MEMO平板电脑则以中等的速度执行运算。

不需要OpenGLES设备在片段着色器中支持highp，但是上面的代码看起来非常需要它。

那是一个完整的片段着色器吗？ 我认为GLES片段着色器要求您指定默认精度或要求您为每个变量指定精度。 我看不到，所以也许有些信息被省略了。