GLES效果

原理参考自的 BugRunner 博客

原图：

效果图：

 void main(void)
 {
    vec2 uv = gl_FragCoord.xy / sketchSize.xy;

    vec3 c = texture2D(Tex, uv).rgb;

    // 声明与初始化
    const int kSize = (MSIZE-1)/2;
    float kernel[MSIZE]; // 2*kSize + 1
    vec3 final_colour = vec3(0.0);

    float Z = 0.0;
    // 1-D：kernel[0 - 2*kSize + 1]
    // kernel[kSize] 权重最大
    for (int j = 0; j <= kSize; ++j)
    {
       kernel[kSize+j] = kernel[kSize-j] = normpdf(float(j), SIGMA);
    }

    vec3 cc;
    float factor;

    for (int i=-kSize; i <= kSize; ++i)
    {
       for (int j=-kSize; j <= kSize; ++j)
       {
          vec2 newUV = vec2(( gl_FragCoord.xy + vec2(float(i),float(j)) ) / sketchSize.xy);
          cc = texture2D(Tex, newUV).rgb;

          // 颜色权重 * 1-D 距离权重 * 1-D 距离权重
          factor = normpdf3(cc-c, BSIGMA) * kernel[kSize+j]*kernel[kSize+i];

          // 用于归一化权重
          Z += factor;
          final_colour += factor*cc;

       }
    }

    gl_FragColor = vec4(final_colour/Z, 1.0);

 }