playcanvas/build/playcanvas.dbg/src/scene/shader-lib/glsl/chunks/render-pass/frag/sampleCatmullRom.js

PlayCanvas WebGL game engine

// Shader function for sampling a 2D texture with Catmull-Rom filtering, using 9 texture samples instead of 16
// based on https://gist.github.com/TheRealMJP/c83b8c0f46b63f3a88a5986f4fa982b1
var glslSampleCatmullRomPS = /* glsl */ `

vec4 SampleTextureCatmullRom(TEXTURE_ACCEPT(tex), vec2 uv, vec2 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.
    vec2 samplePos = uv * texSize;
    vec2 texPos1 = floor(samplePos - 0.5) + 0.5;

    // 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.
    vec2 f = samplePos - texPos1;

    // 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.
    vec2 w0 = f * (-0.5 + f * (1.0 - 0.5 * f));
    vec2 w1 = 1.0 + f * f * (-2.5 + 1.5 * f);
    vec2 w2 = f * (0.5 + f * (2.0 - 1.5 * f));
    vec2 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.
    vec2 w12 = w1 + w2;
    vec2 offset12 = w2 / (w1 + w2);

    // Compute the final UV coordinates we'll use for sampling the texture
    vec2 texPos0 = (texPos1 - 1.0) / texSize;
    vec2 texPos3 = (texPos1 + 2.0) / texSize;
    vec2 texPos12 = (texPos1 + offset12) / texSize;

    vec4 result = vec4(0.0);
    result += texture2DLod(tex, vec2(texPos0.x, texPos0.y), 0.0) * w0.x * w0.y;
    result += texture2DLod(tex, vec2(texPos12.x, texPos0.y), 0.0) * w12.x * w0.y;
    result += texture2DLod(tex, vec2(texPos3.x, texPos0.y), 0.0) * w3.x * w0.y;

    result += texture2DLod(tex, vec2(texPos0.x, texPos12.y), 0.0) * w0.x * w12.y;
    result += texture2DLod(tex, vec2(texPos12.x, texPos12.y), 0.0) * w12.x * w12.y;
    result += texture2DLod(tex, vec2(texPos3.x, texPos12.y), 0.0) * w3.x * w12.y;

    result += texture2DLod(tex, vec2(texPos0.x, texPos3.y), 0.0) * w0.x * w3.y;
    result += texture2DLod(tex, vec2(texPos12.x, texPos3.y), 0.0) * w12.x * w3.y;
    result += texture2DLod(tex, vec2(texPos3.x, texPos3.y), 0.0) * w3.x * w3.y;

    return result;
}
`;

export { glslSampleCatmullRomPS as default };