[CHANGE] - switched to front to back compositing with alpha test

src/modules/directVolumeRendering/WMDirectVolumeRendering.cpp

@@ -242,6 +242,7 @@ void WMDirectVolumeRendering::moduleMain()
                 {
                     warnLog() << "Transfer function texture could not be loaded from " << m_tfLoaderFile->get( true ).file_string() << ".";
                 }
+                m_tfLoaderTrigger->get( true );
             }
 
             ////////////////////////////////////////////////////////////////////////////////////////////////////

src/modules/directVolumeRendering/shaders/WMDirectVolumeRendering-fragment.glsl

@@ -44,10 +44,6 @@
 uniform sampler3D tex0;
 uniform sampler1D TRANSFERFUNCTION_SAMPLER;
 
-// The isovalue to use.
-uniform float u_isovalue1 = 0.33;
-uniform float u_isovalue2 = 0.80;
-
 /////////////////////////////////////////////////////////////////////////////
 // Attributes
 /////////////////////////////////////////////////////////////////////////////
@@ -117,12 +113,12 @@ vec3 getGradient( in vec3 position )
  *
  * \return the color.
  */
-vec4 transferFunction( in float value )
+vec4 transferFunction( float value )
 {
 #ifdef TRANSFERFUNCTION_ENABLED
     return texture1D( TRANSFERFUNCTION_SAMPLER, value );
 #else
-    if ( isZero( value - 0.5, 0.1 ) )   // if not TF has been specified, at least show something
+    if ( isZero( value - 0.5, 0.01 ) )   // if not TF has been specified, at least show something
     {
         return vec4( 1.0, 0.0, 0.0, 0.1 );
     }
@@ -175,39 +171,34 @@ void main()
     vec3 rayEnd = findRayEnd( totalDistance );
 
     // walk along the ray
-    vec4 accumColor = vec4( vec3( 0.0 ), 1.0 );      // the composited color
-    float accumAlpha = 1.0;                          // accumulated transparency of the volume.
-    float depth = gl_FragCoord.z;                    // the depth of the last hit
-    float value;                                     // the current value inside the data
-    float hit = 0.0;                                 // this value will be != 0.0 if something has been hit
+    vec4 dst = vec4( 0.0 );
     while ( currentDistance <= totalDistance )
     {
-        // get current value
-        vec3 rayPoint = rayEnd - ( currentDistance * v_ray );
-        value = texture3D( tex0, rayPoint ).r;
+        // get current value, classify and illuminate
+        vec3 rayPoint = v_rayStart + ( currentDistance * v_ray );
+        vec4 src = localIllumination( rayPoint, transferFunction( texture3D( tex0, rayPoint ).r ) );
+
         // go to next value
         currentDistance += v_stepDistance;
 
-        // classify point in volume and evaluate local illumination model at this position
-        vec4 color = localIllumination( rayPoint,  transferFunction( value ) );
+        // apply front-to-back compositing
+        dst = ( 1.0 - dst.a ) * src + dst;
 
-        // has there ever been something we hit?
-        hit = max( hit, color.a );
-
-        accumColor.rgba = mix( accumColor.rgba, color.rgba, color.a );  // compositing
-        accumAlpha *= ( 1.0 - color.a );                                // compositing: keep track of final alpha value of the background
+        if ( dst.a >= 0.95 )
+            break;
     }
 
+    /*
     // have we hit something which was classified not to be transparent?
     // This is, visually, not needed but useful if volume rendere is used in conjunction with other geometry.
-    if ( isZero( hit ) )
+    if ( isZero( dst.a ) )
     {
         discard;
-    }
+    }*/
 
     // set final color
-    accumColor.a = 1.0 - accumAlpha;
-    gl_FragColor = accumColor;
-    gl_FragDepth = depth;
+    float depth = gl_FragCoord.z;
+    gl_FragColor = dst;
+    gl_FragDepth = depth;                    // the depth of the last hit
 }