[vtkusers] Rendering performance

[Sebastien Jourdain]

Hi Gib,

My first question will be. Are you using one actor for each of your
10000 flat squares ?
If so, the performance limitation may come from the number of actors
involved. One solution to that is to create only one dataset with all
the squares that has only one mapper and actor. To do so, you can
build it by hand or simply use the Glyph filter with your square as a
glyph and another dataset that has the location of those squares.

Seb


On Wed, Nov 24, 2010 at 12:44 AM, Gib Bogle <g.bogle at auckland.ac.nz> wrote:
> I asked about this before, but didn't attract any responses.  I have a
> better understanding of the issue now, so perhaps my questions will make
> more sense.
>
> At regular intervals as my simulation program executes, I am rendering a
> scene that contains mainly about 1000 small spheres (which move) and about
> 10000 flat squares (which do not move).  I have discovered that the
> surprising slowness of the the rendering is caused by the squares, even
> though the spheres have ThetaResolution and PhiResolution both equal to 12,
> which I guess means 144 faces per sphere, i.e. a total of 144,000 faces.  By
> my calculations rendering the scene 288 times with spheres alone takes about
> 4 sec, with the squares alone takes about 20 sec, and with both spheres and
> squares about 24 sec.  That is, 10,000 squares take 5 times as long as 1000
> spheres with 144,000 faces.
>
> Apparently there's something very inefficient about the way I am rendering
> the squares.  Here is the code for tileMapper (which makes squares):
>
> // Create the square
> // Setup points to draw a unit square in the XY plane, at y=0
> vtkSmartPointer<vtkPoints> points = vtkSmartPointer<vtkPoints>::New();
> vtkSmartPointer<vtkCellArray> vertices =
> vtkSmartPointer<vtkCellArray>::New();
> points->InsertNextPoint(-0.5, 0.0, -0.5);
> points->InsertNextPoint( 0.5, 0.0, -0.5);
> points->InsertNextPoint( 0.5, 0.0,  0.5);
> points->InsertNextPoint(-0.5, 0.0,  0.5);
>
> vtkSmartPointer<vtkPolygon> polygon = vtkSmartPointer<vtkPolygon>::New();
> polygon->GetPointIds()->SetNumberOfIds(4); //make a quad
> polygon->GetPointIds()->SetId(0, 0);
> polygon->GetPointIds()->SetId(1, 1);
> polygon->GetPointIds()->SetId(2, 2);
> polygon->GetPointIds()->SetId(3, 3);
>
> //Add the polygon to a list of polygons
> vtkSmartPointer<vtkCellArray> polygons =
> vtkSmartPointer<vtkCellArray>::New();
> polygons->InsertNextCell(polygon);
>
> //Create a PolyData
> vtkSmartPointer<vtkPolyData> polygonPolyData =
> vtkSmartPointer<vtkPolyData>::New();
> polygonPolyData->SetPoints(points);
> polygonPolyData->SetPolys(polygons);
>
> //Create a mapper and actor
> tileMapper = vtkPolyDataMapper::New();
> tileMapper->SetInput(polygonPolyData);
> tileMapper->ScalarVisibilityOff();
>
> The square actors are made like this:
>
> actor = vtkActor::New();
> actor->SetMapper(tileMapper);
> actor->GetProperty()->SetColor(boneColor);
> actor->GetProperty()->SetAmbient(0.5);
> actor->GetProperty()->SetDiffuse(0.2);
> actor->GetProperty()->SetSpecular(0.5);
> actor->SetPosition(pos);
> ren->AddActor(actor);
>
> then not touched again (in the simulations I report times for.)
>
> I'd be very grateful if someone could give me a clue as to what I'm doing
> wrong to make the rendering so slow.
>
> Thanks
> Gib
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