Function getVolumeShaderCommonFunctions

source/MRViewer/MRVolumeShader.cpp:7–80

{

static std::string getVolumeShaderCommonFunctions()
{
    return R"(
  float getVal( in float value )
  {
    return (value - minValue) / (maxValue-minValue);
  }

  float getGradAlphaVal( in float value )
  {
    if ( value < 0.0 || value > 1.0 )
      return 0.0;
    return texture( denseMap, vec2( value, 0.5 ) ).a;
  }

  void swap( inout float a, inout float b )
  {
    float c = a;
    a = b;
    b = c;
  }

  void rayVoxelIntersection( in vec3 minCorner, inout vec3 voxelCoord, in vec3 voxelSize,inout vec3 rayOrg, in vec3 ray )
  {
    vec3 voxelMin = voxelCoord * voxelSize + minCorner - rayOrg;
    vec3 voxelMax = (voxelCoord + vec3(1.0,1.0,1.0) ) * voxelSize + minCorner - rayOrg;
    vec3 minInt = voxelMin / ray;
    vec3 maxInt = voxelMax / ray;
    if ( ray.x < 0.0 )
        swap( minInt.x, maxInt.x );
    if ( ray.y < 0.0 )
        swap( minInt.y, maxInt.y );
    if ( ray.z < 0.0 )
        swap( minInt.z, maxInt.z );

    bvec3 goodRayComp = greaterThan( abs( ray ), vec3(0.001,0.001,0.001) ); // discard small ray components
    float absMinInt = -1.0e20; // just some small value
    if ( goodRayComp.x && minInt.x > absMinInt )
        absMinInt = minInt.x;
    if ( goodRayComp.y && minInt.y > absMinInt )
        absMinInt = minInt.y;
    if ( goodRayComp.z && minInt.z > absMinInt )
        absMinInt = minInt.z;

    rayOrg = rayOrg + ray * absMinInt;

    float absMaxInt = 1.0e20; // just some big value
    int absMaxIntId = 3; // to have "else" block if ray is zero for some reason
    if ( goodRayComp.x && maxInt.x < absMaxInt )
    {
        absMaxIntId = 0;
        absMaxInt = maxInt.x;
    }
    if ( goodRayComp.y && maxInt.y < absMaxInt )
    {
        absMaxIntId = 1;
        absMaxInt = maxInt.y;
    }