Lib Pom - Shader API

import lib-sampler.glsl

//: param auto is_2d_view

uniform bool isTextureView;



//: param auto channel_displacement

uniform SamplerSparse displacement_tex;



//: param custom { "label": "Enable", "default": false, "group": "Parallax Occlusion Mapping" }

uniform bool usePOM;



//: param custom { "label": "Strength", "default": 1.0, "min": 0.01, "max": 10.0, "group": "Parallax Occlusion Mapping" }

uniform float pomStrength;



//: param custom { "label": "Minimum samples", "default": 4, "min": 1, "max": 64, "group": "Parallax Occlusion Mapping" }

uniform int minPOMSamples;



//: param custom { "label": "Maximum samples", "default": 16, "min": 1, "max": 64, "group": "Parallax Occlusion Mapping" }

uniform int maxPOMSamples;

vec2 getParallaxOffset(SparseCoord coord, vec3 viewTS)

{

  if (!usePOM || isTextureView || !displacement_tex.is_set) return vec2(0.0);



  vec2 dfdx,dfdy;

  textureSparseQueryGrad(dfdx, dfdy, displacement_tex, coord);



  // Convention: 1.0 is top, -1.0 is bottom - POM is always inward, no extrusion

  int nbSteps = int(mix(maxPOMSamples, minPOMSamples, viewTS.z));

  float amplitude = 4.0 * pomStrength / (HEIGHT_FACTOR * abs(viewTS.z) * nbSteps);

  vec3 rayStep = vec3(-amplitude * viewTS.xy, -2.0 / nbSteps);



  // Raymarch until we cross the surface

  vec3 rayPos = vec3(coord.tex_coord, 1.0);

  float prevHeight;

  float currHeight = getDisplacement(textureGrad(displacement_tex.tex, rayPos.xy, dfdx, dfdy));

  int i = 0;

  do {

    rayPos += rayStep;

    prevHeight = currHeight;

    currHeight = getDisplacement(textureGrad(displacement_tex.tex, rayPos.xy, dfdx, dfdy));

    i++;

  } while (i < nbSteps && currHeight < rayPos.z);



  // Binary search with linear interpolation to refine intersection

  vec3 prevRayPos = rayPos - rayStep;

  vec3 newRayPos = prevRayPos;

  float newHeight = prevHeight;

  i = 0;

  while (i < 3 && abs(newHeight - newRayPos.z) > 1e-3) {

    float prevDelta = prevRayPos.z - prevHeight;

    float delta = currHeight - rayPos.z;

    newRayPos = (prevDelta * rayPos + delta * prevRayPos) / (prevDelta + delta);

    newHeight = getDisplacement(textureGrad(displacement_tex.tex, newRayPos.xy, dfdx, dfdy));



    if (newHeight > newRayPos.z) {

      currHeight = newHeight;

      rayPos = newRayPos;

    } else {

      prevHeight = newHeight;

      prevRayPos = newRayPos;

    }



    i++;

  }



  return newRayPos.xy - coord.tex_coord;

}

void applyParallaxOffset(inout V2F inputs, vec3 viewTS)

{

  vec2 offset = getParallaxOffset(inputs.sparse_coord, viewTS);

  if (any(notEqual(offset,vec2(0.0)))) {

    inputs.tex_coord += offset;

    inputs.sparse_coord = getSparseCoord(inputs.tex_coord);

  }

}