Efficient Bicubic filtering code in GLSL?

前端 未结 8 1811
感动是毒
感动是毒 2021-01-30 06:11

I\'m wondering if anyone has complete, working, and efficient code to do bicubic texture filtering in glsl. There is this:

http://www.codeproject.com/Articles/236394/Bi-

相关标签:
8条回答
  • 2021-01-30 06:30

    The missing function cubic() in JAre's answer could look like this:

    vec4 cubic(float x)
    {
        float x2 = x * x;
        float x3 = x2 * x;
        vec4 w;
        w.x =   -x3 + 3*x2 - 3*x + 1;
        w.y =  3*x3 - 6*x2       + 4;
        w.z = -3*x3 + 3*x2 + 3*x + 1;
        w.w =  x3;
        return w / 6.f;
    }
    

    It returns the four weights for cubic B-Spline.

    It is all explained in NVidia Gems.

    0 讨论(0)
  • 2021-01-30 06:34

    I found this implementation which can be used as a drop-in replacement for texture() (from http://www.java-gaming.org/index.php?topic=35123.0 (one typo fixed)):

    // from http://www.java-gaming.org/index.php?topic=35123.0
    vec4 cubic(float v){
        vec4 n = vec4(1.0, 2.0, 3.0, 4.0) - v;
        vec4 s = n * n * n;
        float x = s.x;
        float y = s.y - 4.0 * s.x;
        float z = s.z - 4.0 * s.y + 6.0 * s.x;
        float w = 6.0 - x - y - z;
        return vec4(x, y, z, w) * (1.0/6.0);
    }
    
    vec4 textureBicubic(sampler2D sampler, vec2 texCoords){
    
       vec2 texSize = textureSize(sampler, 0);
       vec2 invTexSize = 1.0 / texSize;
    
       texCoords = texCoords * texSize - 0.5;
    
    
        vec2 fxy = fract(texCoords);
        texCoords -= fxy;
    
        vec4 xcubic = cubic(fxy.x);
        vec4 ycubic = cubic(fxy.y);
    
        vec4 c = texCoords.xxyy + vec2 (-0.5, +1.5).xyxy;
    
        vec4 s = vec4(xcubic.xz + xcubic.yw, ycubic.xz + ycubic.yw);
        vec4 offset = c + vec4 (xcubic.yw, ycubic.yw) / s;
    
        offset *= invTexSize.xxyy;
    
        vec4 sample0 = texture(sampler, offset.xz);
        vec4 sample1 = texture(sampler, offset.yz);
        vec4 sample2 = texture(sampler, offset.xw);
        vec4 sample3 = texture(sampler, offset.yw);
    
        float sx = s.x / (s.x + s.y);
        float sy = s.z / (s.z + s.w);
    
        return mix(
           mix(sample3, sample2, sx), mix(sample1, sample0, sx)
        , sy);
    }
    

    Example: Nearest, bilinear, bicubic:

    The ImageData of this image is

    {{{0.698039, 0.996078, 0.262745}, {0., 0.266667, 1.}, {0.00392157, 
       0.25098, 0.996078}, {1., 0.65098, 0.}}, {{0.996078, 0.823529, 
       0.}, {0.498039, 0., 0.00392157}, {0.831373, 0.00392157, 
       0.00392157}, {0.956863, 0.972549, 0.00784314}}, {{0.909804, 
       0.00784314, 0.}, {0.87451, 0.996078, 0.0862745}, {0.196078, 
       0.992157, 0.760784}, {0.00392157, 0.00392157, 0.498039}}, {{1., 
       0.878431, 0.}, {0.588235, 0.00392157, 0.00392157}, {0.00392157, 
       0.0666667, 0.996078}, {0.996078, 0.517647, 0.}}}
    

    I tried to reproduce this (many other interpolation techniques)

    but they have clamped padding, while I have repeating (wrapping) boundaries. Therefore it is not exactly the same.

    It seems this bicubic business is not a proper interpolation, i.e. it does not take on the original values at the points where the data is defined.

    0 讨论(0)
提交回复
热议问题