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- // Samples a texture with Catmull-Rom filtering, using 9 texture fetches instead of 16.
- // See http://vec3.ca/bicubic-filtering-in-fewer-taps/ for more details
- float4 SampleTextureCatmullRom(in Texture2D<float4> tex, in SamplerState linearSampler, in float2 uv, in float2 texSize)
- {
- // We're going to sample a a 4x4 grid of texels surrounding the target UV coordinate. We'll do this by rounding
- // down the sample location to get the exact center of our "starting" texel. The starting texel will be at
- // location [1, 1] in the grid, where [0, 0] is the top left corner.
- float2 samplePos = uv * texSize;
- float2 texPos1 = floor(samplePos - 0.5f) + 0.5f;
- // Compute the fractional offset from our starting texel to our original sample location, which we'll
- // feed into the Catmull-Rom spline function to get our filter weights.
- float2 f = samplePos - texPos1;
- //float2 f2 = f * f;
- // Compute the Catmull-Rom weights using the fractional offset that we calculated earlier.
- // These equations are pre-expanded based on our knowledge of where the texels will be located,
- // which lets us avoid having to evaluate a piece-wise function.
- float2 w0 = f * ( -0.5 + f * (1.0 - 0.5*f));
- float2 w1 = 1.0 + f * f * (1.5*f - 2.5);
- float2 w2 = f * ( 0.5 + f * (2.0 - 1.5*f) );
- float2 w3 = f * f * (-0.5 + 0.5 * f);
- // Work out weighting factors and sampling offsets that will let us use bilinear filtering to
- // simultaneously evaluate the middle 2 samples from the 4x4 grid.
- float2 w12 = w1 + w2;
- float2 offset12 = w2 / (w1 + w2);
- // Compute the final UV coordinates we'll use for sampling the texture
- float2 texPos0 = texPos1 - 1;
- float2 texPos3 = texPos1 + 2;
- float2 texPos12 = texPos1 + offset12;
- texPos0 /= texSize;
- texPos3 /= texSize;
- texPos12 /= texSize;
- float4 result = 0.0f;
- result += tex.SampleLevel(linearSampler, float2(texPos0.x, texPos0.y), 0.0f) * w0.x * w0.y;
- result += tex.SampleLevel(linearSampler, float2(texPos12.x, texPos0.y), 0.0f) * w12.x * w0.y;
- result += tex.SampleLevel(linearSampler, float2(texPos3.x, texPos0.y), 0.0f) * w3.x * w0.y;
- result += tex.SampleLevel(linearSampler, float2(texPos0.x, texPos12.y), 0.0f) * w0.x * w12.y;
- result += tex.SampleLevel(linearSampler, float2(texPos12.x, texPos12.y), 0.0f) * w12.x * w12.y;
- result += tex.SampleLevel(linearSampler, float2(texPos3.x, texPos12.y), 0.0f) * w3.x * w12.y;
- result += tex.SampleLevel(linearSampler, float2(texPos0.x, texPos3.y), 0.0f) * w0.x * w3.y;
- result += tex.SampleLevel(linearSampler, float2(texPos12.x, texPos3.y), 0.0f) * w12.x * w3.y;
- result += tex.SampleLevel(linearSampler, float2(texPos3.x, texPos3.y), 0.0f) * w3.x * w3.y;
- return result;
- }
- Texture2D<float4> g_Tx;
- sampler g_S;
- float4 main( float2 uv : TEXCOORD0 ) : SV_Target
- {
- return SampleTextureCatmullRom( g_Tx, g_S, uv, float2(512,512) );
- }
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