Nvidia-Cubic-Interpolation-Sample.cg

/**
 * Taken from https://developer.nvidia.com/gpugems/gpugems2/part-iii-high-quality-rendering/chapter-20-fast-third-order-texture-filtering
 */

float4 bspline_1d_fp(
  float coord_source: TEXCOORD0,
  uniform sampler1D tex_source,  // source texture
  uniform sampler1D tex_hg,      // filter offsets and weights
  uniform float e_x,             // source texel size
  uniform float size_source      // source texture size
) : COLOR {
  // calc filter texture coordinates where [0,1] is a single texel
  // (can be done in vertex program instead)
  float coord_hg = coord_source * size_source – 0.5f;
  // fetch offsets and weights from filter texture
  float3 hg_x = tex1D( tex_hg, coord_hg ).xyz;      // determine linear sampling coordinates
  float coord_source1 = coord_source + hg_x.x * e_x;
  float coord_source0 = coord_source - hg_x.y * e_x;      // fetch two linearly interpolated inputs
  float4 tex_source0 = tex1D(tex_source, coord_source0);
  float4 tex_source1 = tex1D(tex_source, coord_source1);      // weight linear samples
  tex_source0 = lerp(tex_source0, tex_source1, tex_hg_x.z);
  return tex_source0;
}