Add a checkbox for toggling opacity in 3d redering

By default, regions with higher density region have higher opacity. In the
current implementation, there is no option to change this behavior. At
least, I cannot find it. So I added a checkbox for inverting the opacity
mapping. This is useful when the high-density region is outside the main
volume.

Author: WeiqunZhang

Docs/Amrvis.tex

@@ -294,6 +294,7 @@ \subsubsection{Interface Controls}
 			to draw.
     \item [Autodraw]    Automatically render the image while rotating.
 			As with {\bf Draw}, the first image takes longer.
+    \item [Invert Opacity] Useful when high-density regions are outside the volume.
     \item [Trans]       Reread the transfer functions.
     \item [Lights]      Allows the user to set the rendering lighting parameters.
     \item[Light/Value]  This menu shows the volume rendering

PltApp.H

@@ -162,6 +162,7 @@ private:
   Widget wAttach, wDetachTopLevel;
 #if defined(BL_VOLUMERENDER) || defined(BL_PARALLELVOLUMERENDER)
   Widget wAutoDraw;
+  Widget wInvertOpacity;
   Widget wLWambient, wLWdiffuse, wLWspecular, wLWshiny;
   Widget wLWminOpacity, wLWmaxOpacity;
   Widget wCurrentRenderMode, wCurrentClassify;
@@ -229,7 +230,7 @@ private:
   ProjectionPicture *projPicturePtr;
   ViewTransform	viewTrans;
   bool lightingModel, showing3dRender, preClassify, lightingWindowExists;
-
+  bool invert_opacity = false;
 #endif
 
   void PltAppInit(bool bSubVolume = false);           // called by constructors
@@ -308,6 +309,7 @@ private:
   void DoRenderModeMenu(Widget, XtPointer, XtPointer);
   void DoClassifyMenu(Widget, XtPointer, XtPointer);
   void DoAutoDraw(Widget, XtPointer, XtPointer);
+  void SetInvertOpacity(Widget, XtPointer, XtPointer);
   void DoCreateLightingWindow(Widget, XtPointer, XtPointer);
   void DoDoneLightingWindow(Widget, XtPointer, XtPointer);
   void DoApplyLightingWindow(Widget, XtPointer, XtPointer);

PltApp.cpp

@@ -1133,6 +1133,11 @@ void PltApp::PltAppInit(bool bSubVolume) {
     XtVaCreateManagedWidget("Autodraw", xmToggleButtonGadgetClass, wMenuPulldown,
 			    XmNmnemonic, 'A', XmNset, false, NULL);
   AddStaticCallback(wAutoDraw, XmNvalueChangedCallback, &PltApp::DoAutoDraw);
+
+  wInvertOpacity =
+    XtVaCreateManagedWidget("Invert Opacity", xmToggleButtonGadgetClass, wMenuPulldown,
+			    XmNmnemonic, 'I', XmNset, false, NULL);
+  AddStaticCallback(wInvertOpacity, XmNvalueChangedCallback, &PltApp::SetInvertOpacity);
 
   wid = XtVaCreateManagedWidget("Lighting...",
 				xmPushButtonGadgetClass, wMenuPulldown,

PltApp3D.cpp

@@ -782,6 +782,20 @@ void PltApp::DoAutoDraw(Widget, XtPointer, XtPointer) {
   DoExposeTransDA();
 }
 
+// -------------------------------------------------------------------
+void PltApp::SetInvertOpacity(Widget, XtPointer, XtPointer) {
+  if(XmToggleButtonGetState(wInvertOpacity)) {
+    invert_opacity = true;
+  } else {
+    invert_opacity = false;
+  }
+  VolRender *volRenderPtr = projPicturePtr->GetVolRenderPtr();
+  if (volRenderPtr && volRenderPtr->GetInvertOpacity() != invert_opacity) {
+    volRenderPtr->SetInvertOpacity(invert_opacity);
+    volRenderPtr->InvalidateSWFData();
+    volRenderPtr->InvalidateVPData();
+  }
+}
 
 // -------------------------------------------------------------------
 void PltApp::DoRenderModeMenu(Widget w, XtPointer item_no, XtPointer /*client_data*/) {

VolRender.H

@@ -92,6 +92,8 @@ class VolRender {
     void SetTransferProperties();
     void SetLighting(Real ambient, Real diffuse, Real specular, Real shiny,
 		     Real minRay, Real maxRay);
+    void SetInvertOpacity(bool a_invert_opacity) { invert_opacity = a_invert_opacity; }
+    bool GetInvertOpacity() { return invert_opacity; }
     Real GetDiffuse() { return diffuseMat; }
     Real GetAmbient() { return ambientMat; }
     Real GetSpecular() { return specularMat; }
@@ -102,6 +104,7 @@ class VolRender {
   private:
     Real diffuseMat, shinyMat, specularMat, ambientMat;
     Real vpLen, vpAspect;
+    bool invert_opacity = false;
     bool lightingModel, preClassify;
     bool bDrawAllBoxes;
     int  voxelFields;

VolRender.cpp

@@ -273,7 +273,7 @@ void VolRender::MakeSWFData(amrex::DataServices *dataServicesPtr,
     int grows   = gbox.length(Amrvis::XDIR);
     int gcols   = gbox.length(Amrvis::YDIR);
     //int gplanes = gbox.length(Amrvis::ZDIR);
-    
+
     int gcolsgrowstmp(gcols * grows);
     int gpgcgrtmp, gcgrowstmp;
     for(int gp(gostartp); gp <= goendp; ++gp) {
@@ -285,6 +285,9 @@ void VolRender::MakeSWFData(amrex::DataServices *dataServicesPtr,
           dat = dataPoint[gcgrowstmp + gr];
           dat = max(dat,gmin); // clip data if out of range
           dat = min(dat,gmax);
+          if (invert_opacity) {
+            dat = gmax - (dat-gmin);
+          }
           chardat = (char) (((dat - gmin) * oneOverGDiff) * cSlotsAvail);
           chardat += (char) iPaletteStart;
 	  int gprev = gostartp + goendp - gp;