[vtkusers] Volume Rendering, cell mode, and rotation optimization - VTK macro bug/issue?

[Richard Frank]

On researching my previous question about how the volume rendering is made lower resolution during rotation,
I did some tracing of the code, and found what I believe is a problem related to a Macro.

This is the section of code that determines whether the sampling  distance is computed on the fly for the GPURenderMode:

case vtkSmartVolumeMapper::GPURenderMode:
    ...
      usedMapper->SetAutoAdjustSampleDistances(
        ren->GetRenderWindow()->GetDesiredUpdateRate()>=
        this->InteractiveUpdateRate);
      usedMapper->Render(ren, vol);
      break;
 

Here it seems that SetAutoAdjustSampleDistance(int) if passed 0 will turn off auto adjusting sampling distance.

If I look at 

ren->GetRenderWindow()->GetDesiredUpdateRate() it is equal to 0.0001;

this->InteractiveUpdateRate == 1.0;

so, GetDesiredUpdateRate is not greater than or equal to InteractiveUpdateRate,
and so SetAutoAdjustSampleDistances() should be passed 0 (or false) and turned off.

But it's not.

SetAutoAdjustSampleDistance is defined as some macros
/ Description:
  // If AutoAdjustSampleDistances is on, the the ImageSampleDistance
  // will be varied to achieve the allocated render time of this
  // prop (controlled by the desired update rate and any culling in
  // use).
  vtkSetClampMacro( AutoAdjustSampleDistances, int, 0, 1 );
  vtkGetMacro( AutoAdjustSampleDistances, int );
  vtkBooleanMacro( AutoAdjustSampleDistances, int );


if I change the code to 

int val = ren->GetRenderWindow()->GetDesiredUpdateRate()>=
        this->InteractiveUpdateRate; 

usedMapper->SetAutoAdjustSampleDistances(val);

val is 0 and still doesn't turn it off.


HOWEVER if I change the code to 


usedMapper->SetAutoAdjustSampleDistances(0); 

IT WORKS - the Auto Adjustment is off and I get smooth rotations.

Seems odd to me, and perhaps a bug with the macro definition?

I'm using Windows Visual Studio 7, but we also see this on Ubuntu Linux with gcc 

Can someone verify?


Thanks

Rick


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