     }
 
     // early ray termination
-    if (fragmentColor.a > 0.999)
+    if (fragmentColor.a > EARLY_RAY_TERMINATION_ALPHA)
       break;
 
     currentPos_eye += step_eye;

uniform sampler3D volumeSampler;

const float DEPTH_NOT_SET = -10.0f;

#define transferFunctionRowCount 64.0f


      accumulatedOutputColor = blend(accumulatedOutputColor, currentFragment.color);
    }

    if (finalColor.a > EARLY_RAY_TERMINATION_ALPHA)
      break;

    // break; // just the first fragment
