better blending of background image

Graphics/drawContext.cpp

@@ -481,8 +481,8 @@ void drawContext::drawBackgroundImage(bool threeD)
   glBlendFunc(GL_SRC_ALPHA, GL_ONE_MINUS_SRC_ALPHA);
   glEnable(GL_TEXTURE_2D);
   glBindTexture(GL_TEXTURE_2D, _bgImageTexture);
+  glTexEnvi(GL_TEXTURE_ENV, GL_TEXTURE_ENV_MODE, GL_REPLACE);
   glBegin(GL_QUADS);
-  glColor4ubv((GLubyte *) & CTX::instance()->color.bg);
   if(threeD){
     glTexCoord2f(1.0f, 1.0f); glVertex2d(x+w, y);
     glTexCoord2f(1.0f, 0.0f); glVertex2d(x+w, y+h);

tutorial/t5.geo

@@ -158,3 +158,9 @@ Volume(186) = {theloops[]} ;
 // with numbers 1 to 5 in the `For' loop):
 
 Physical Volume (10) = 186 ;
+
+// We could make only part of the model visible to only mesh this subset:
+//
+// Hide "*";
+// Recursive Show { Volume{129}; }
+// Mesh.MeshOnlyVisible=1;