       accumulatedOutputColor = blend(accumulatedOutputColor, currentFragment.color);
     }
 
-    if (finalColor.a > 0.999)
+    if (finalColor.a > EARLY_RAY_TERMINATION_ALPHA)
       break;
 
     // break; // just the first fragment

uniform sampler3D volumeSampler;

const float DEPTH_NOT_SET = -10.0f;

#define transferFunctionRowCount 64.0f


    }

    // early ray termination
    if (fragmentColor.a > EARLY_RAY_TERMINATION_ALPHA)
      break;

    currentPos_eye += step_eye;
