TextureUtils Lanczos2 issue

antokhio · June 30, 2026, 7:09pm

Hi, there seems to be a broken function in the:

VL.Stride.Runtime/src/Effects/Common/TextureUtils.sdsl

464cd0d7e


      
          }
          
          float4 resampler(float4 x)
          {
              float wa = lanczos2_window_sinc * Pi;
              float wb = lanczos2_sinc * Pi;
              float wab = wa * wb;
              return x == float4(0, 0, 0, 0) ?  float4(wab, wab, wab, wab) : sin(x * wa) * sin(x * wb) / (x * x);
          }
          
          float4 SampleLanczos2(in Texture2D text, in float2 uv)
          {
              float3 color;
              float3 E;
              float2 qt_TexCoord0 = uv;
          
              float2 dx = float2(1.0, 0.0);
              float2 dy = float2(0.0, 1.0);
          
              float w, h;
              text.GetDimensions(w, h);

Looks like somebody try to port this from Cg and wasn’t quite successful, leading to:

github.com/vvvv/VL.StandardLibs

VL.Stride.Runtime/src/Effects/TextureFX/Utils/Resize_TextureFX.sdsl

464cd0d7e


      
              uint Mode = 1;
          
              stage override float4 Shading()
              {
                  switch (Mode)
                  {
                      case 0: return Texture0.Sample(PointSampler, streams.TexCoord);
                      case 1: return Texture0.Sample(LinearSampler, streams.TexCoord);
                      case 2: return SampleCubicBSpline(Texture0, LinearSampler, streams.TexCoord);
                      case 3: return SampleCubicCatmullRom(Texture0, LinearSampler, streams.TexCoord);
                      // case 4: return SampleLanczos2(Texture0, streams.TexCoord);
                  }
          
                  return 1;
              }
          };

github.com/vvvv/VL.StandardLibs

VL.Stride.TextureFX/shaders/Filters/Distortion/Transform_TextureFX.sdsl

464cd0d7e


      
          
              float4 Filter(float4 tex0col)
              {
                  float2 uv = mul(float4((streams.TexCoord * 2 - 1) * float2(1,-1) * .5, 0, 1), Transform).xy * float2(1,-1) + 0.5;
          
                  switch (InterpolationMode)
                  {
                      case 0: return Texture0.Sample(CustomSampler, uv);
                      case 1: return SampleCubicBSpline(Texture0, CustomSampler, uv);
                      case 2: return SampleCubicCatmullRom(Texture0, CustomSampler, uv);
                      // case 4: return SampleLanczos2(Texture0, uv);
                  }
          
                  return 1;
              }
          };

github.com/vvvv/VL.StandardLibs

VL.Stride.Runtime/src/Effects/TextureFX/Utils/Crop_Internal_TextureFX.sdsl

464cd0d7e


      
              stage override float4 Shading()
              {
                  float2 uv = streams.TexCoord * Size + TopLeft;
              
                  switch (Mode)
                  {
                      case 0: return Texture0.Sample(PointSampler, uv);
                      case 1: return Texture0.Sample(LinearSampler, uv);
                      case 2: return SampleCubicBSpline(Texture0, LinearSampler, uv);
                      case 3: return SampleCubicCatmullRom(Texture0, LinearSampler, uv);
                      // case 4: return SampleLanczos2(Texture0, uv);
                  }
          
                  return 1;
              }
          };

I can replace it with:

gist.github.com

https://gist.github.com/antokhio/c294bbad57608bedc8e08d7b264e1666

Lanczos2.sdsl

shader Lanczos2
{
    // ----------- Custom Optimized Lanczos2 Filter
    static const float lanczos2_window_sinc = 0.4;
    static const float lanczos2_sinc = 1.0;
    static const float lanczos2_ar_strength = 0.65;
    static const float lanczos2_res = 0.98;
    static const float PI = 3.14159265359;

    // Component-wise safe resampler (avoids branching and bool4 ternary errors)

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