ENH: Add timestamp check on quality adjustment.

If a high-res texture is already loaded and if it will not have to
be re-loaded during the render, then keep it rather than forcing
generation of a low-res texture during interactive renders.

Rendering/vtkImageResliceMapper.cxx

@@ -120,7 +120,8 @@ void vtkImageResliceMapper::Render(vtkRenderer *ren, vtkImageSlice *prop)
     int *isize = this->GetInput()->GetDimensions();
     int maxisize = (isize[0] > isize[1] ? isize[0] : isize[1]);
     maxisize = (isize[2] > maxisize ? isize[2] : maxisize);
-    if (maxisize <= maxrsize && maxisize <= 1024)
+    if (maxisize <= maxrsize && maxisize <= 1024 &&
+        prop->GetRedrawMTime() > this->SliceMapper->LoadTime)
       {
       this->InternalResampleToScreenPixels =
         (prop->GetAllocatedRenderTime() >= 1.0);

Rendering/vtkImageSliceMapper.h

@@ -160,6 +160,7 @@ protected:
     unsigned char *data, int xsize, int ysize,
     const double imageSpacing[3], vtkImageProperty *property);
 
+  vtkTimeStamp LoadTime;
   int SliceNumber;
   int SliceNumberMinValue;
   int SliceNumberMaxValue;

Rendering/vtkOpenGLImageSliceMapper.h

@@ -92,7 +92,6 @@ protected:
   // Check various OpenGL capabilities
   void CheckOpenGLCapabilities(vtkOpenGLRenderWindow *renWin);
 
-  vtkTimeStamp LoadTime;
   long Index; // OpenGL ID for texture or display list
   long FragmentShaderIndex; // OpenGL ID for fragment shader
   vtkRenderWindow *RenderWindow; // RenderWindow used for previous render