@edsilv/ami.js/src/shaders/shaders.vr.secondpass.fragment.js

<p align="center"> <img src="https://user-images.githubusercontent.com/214063/46479857-4cd66e80-c7f0-11e8-9585-5748409c9490.png" width="60%"> </p>

import shadersInterpolation from './interpolation/shaders.interpolation';
import shadersIntersectBox from './helpers/shaders.helpers.intersectBox';

export default class ShadersFragment {
  // pass uniforms object
  constructor(uniforms) {
    this._uniforms = uniforms;
    this._functions = {};
    this._main = '';
  }

  functions() {
    if (this._main === '') {
      // if main is empty, functions can not have been computed
      this.main();
    }

    let content = '';
    for (let property in this._functions) {
      content += this._functions[property] + '\n';
    }

    return content;
  }

  uniforms() {
    let content = '';
    for (let property in this._uniforms) {
      let uniform = this._uniforms[property];
      content += `uniform ${uniform.typeGLSL} ${property}`;

      if (uniform && uniform.length) {
        content += `[${uniform.length}]`;
      }

      content += ';\n';
    }

    return content;
  }

  main() {
    // need to pre-call main to fill up the functions list
    this._main = `
void getIntensity(in vec3 dataCoordinates, out float intensity, out vec3 gradient){

  vec4 dataValue = vec4(0., 0., 0., 0.);
  ${shadersInterpolation(this, 'dataCoordinates', 'dataValue', 'gradient')}

  intensity = dataValue.r;

  // rescale/slope
  intensity = intensity*uRescaleSlopeIntercept[0] + uRescaleSlopeIntercept[1];
  // window level
  float windowMin = uWindowCenterWidth[0] - uWindowCenterWidth[1] * 0.5;
  intensity = ( intensity - windowMin ) / uWindowCenterWidth[1];
}

void main(void) {
  const int maxSteps = 1024;
  
    //
    vec2 texc = vec2(((vProjectedCoords.x / vProjectedCoords.w) + 1.0 ) / 2.0,
                  ((vProjectedCoords.y / vProjectedCoords.w) + 1.0 ) / 2.0 );
    //The back position is the world space position stored in the texture.
    vec3 backPosNormalized = texture2D(uTextureBack, texc).xyz;
    
    //
    vec3 tBack = vec3(backPosNormalized.x * (uWorldBBox[1] - uWorldBBox[0]) + uWorldBBox[0],
                       backPosNormalized.y * (uWorldBBox[3] - uWorldBBox[2]) + uWorldBBox[2],
                       backPosNormalized.z * (uWorldBBox[5] - uWorldBBox[4]) + uWorldBBox[4]);
    vec3 tFront = vec3(vPos.x, vPos.y, vPos.z);

    // gl_FragColor = vec4(tFront.xyz, 1.);
    // // gl_FragColor = vec4(backPosNormalized.xyz, 1.);
    // return;
  
  // the ray
  vec3 rayOrigin = cameraPosition;
  float dist = distance(tBack, tFront);
  vec3 rayDirection = normalize(tBack - tFront);
  // gl_FragColor = vec4(rayDirection.xyz, 1.);
  // return;

  // init the ray marching
  float tCurrent = 0.;
  float tStep = dist / float(uSteps);
  // gl_FragColor = vec4(tStep, 1., 1., 1.);
  // return;

  vec4 accumulatedColor = vec4(0.0);
  float accumulatedAlpha = 0.0;

  for(int rayStep = 0; rayStep < maxSteps; rayStep++){
    vec3 currentPosition = tFront + rayDirection * tCurrent;
    // some non-linear FUN
    // some occlusion issue to be fixed
    vec3 transformedPosition = currentPosition; //transformPoint(currentPosition, uAmplitude, uFrequence);
    // world to data coordinates
    // rounding trick
    // first center of first voxel in data space is CENTERED on (0,0,0)
    vec4 dataCoordinatesRaw = uWorldToData * vec4(transformedPosition, 1.0);
    vec3 currentVoxel = vec3(dataCoordinatesRaw.x, dataCoordinatesRaw.y, dataCoordinatesRaw.z);
    float intensity = 0.0;
    vec3 gradient = vec3(0., 0., 0.);
    getIntensity(currentVoxel, intensity, gradient);

    vec4 colorSample;
    float alphaSample;
    if(uLut == 1){
      vec4 colorFromLUT = texture2D( uTextureLUT, vec2( intensity, 1.0) );
      // 256 colors
      colorSample = colorFromLUT;
      alphaSample = colorFromLUT.a;
    }
    else{
      alphaSample = intensity;
      colorSample.r = colorSample.g = colorSample.b = intensity * alphaSample;
    }

    alphaSample = 1.0 - pow((1.0- alphaSample),tStep*uAlphaCorrection);
    alphaSample *= (1.0 - accumulatedAlpha);

    accumulatedColor += alphaSample * colorSample;
    accumulatedAlpha += alphaSample;

    tCurrent += tStep;

    if(tCurrent > dist || accumulatedAlpha >= 1.0 ) break;
  }

  gl_FragColor = vec4(accumulatedColor.xyz, accumulatedAlpha);
}
   `;
  }

  compute() {
    let shaderInterpolation = '';
    // shaderInterpolation.inline(args) //true/false
    // shaderInterpolation.functions(args)

    return `
// uniforms
${this.uniforms()}

// varying (should fetch it from vertex directly)
varying vec4      vPos;
varying vec4 vProjectedCoords;

// tailored functions
${this.functions()}

// main loop
${this._main}
      `;
  }
}