[vtkusers] Z-buffer and picking

[Julian Ibarz]

Hello everyone,

I'm actually working on a picking that don't draw all the objets of the
scene but only the pickable objects. In fact my scene contains for example
400 actors of 4 types of datas. My user want to select only one type of
data. But he wants to select only the actors visibles.

So to not draw all the actors on the pick rendering (i use
vtkVisibleCellSelector for personnal implementation reason) I change a
little VTK and I don't erase the z-buffer on the pick rendering. This
permits to me to render only the actors pickable and to be sure that they
are visible when all the actors are rendered.

This works when the selection area is a point. But when the selection area
is a rectangle the z-buffer is reset to 0 and I don't know where. A
developper of VTK could tell me where in the code the z-buffer is set to 0
and why ? (by default a clear z-buffer is equal to 1, the infinite, 0 is the
near plan).

This is the key code that shows the setting 0 of the z-buffer (in java ) :

vtkFloatArray beforeNative = new vtkFloatArray();
        canvas.GetRenderWindow().GetZbufferData(firstPoint[0],
firstPoint[1], secondPoint[0], secondPoint[1], beforeNative);
        float[] before = beforeNative.GetJavaArray();

// Making my picking

vtkFloatArray afterNative = new vtkFloatArray();
        canvas.GetRenderWindow().GetZbufferData(firstPoint[0],
firstPoint[1], secondPoint[0], secondPoint[1], afterNative);

        float[] after = afterNative.GetJavaArray();

        System.out.println("Z-BUFFER : ");
        for(int i = 0 ; i < before.length ; ++i)
        {
            System.out.println(before[i] + " -> " + after[i]);
        }

The output for a point selection :

Z-BUFFER :
0.37655056 -> 0.37655056

The output for a rectangle selection :

Z-BUFFER :
0.0 -> 0.4381339
0.0 -> 0.43666053
0.0 -> 0.43538022
0.0 -> 0.4345476
0.0 -> 0.43371505
0.0 -> 0.43288243
0.0 -> 0.43204987
0.0 -> 0.43142706
0.0 -> 0.43115902
0.0 -> 0.43089098
0.0 -> 0.43062294
0.0 -> 0.4303549
0.0 -> 0.43019688
0.0 -> 0.43046153
0.0 -> 0.43072623
0.0 -> 0.43099087
0.0 -> 0.43125558
0.0 -> 0.43152028
0.0 -> 0.43230826
0.0 -> 0.43310922
0.0 -> 0.4339102
0.0 -> 0.43471116
0.0 -> 0.43551213

Any suggestion ?

-- 
Julian Ibarz
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