[vtkusers] Bug in vtkRenderer with BackingStoreOn when resizing window

[Vladan Bato]

Hi,
there is a bug in vtkRenderer that makes the program crash when you 
resize the window (by making it bigger) if the renderer has backing 
store activated.

The attached example (modified Cone5.tcl) reproduces the problem.
The only difference is the

ren1 BackingStoreOn

line.

If you resize the window by making it bigger (e.g. dragging the right 
border to the right), the program will crash with a segmentation fault.

Upon investigation I think the problem is in the vtkRenderer::Render()
function. When you resize the window, the Render() function thinks that 
the backing store is still valid and tries to copy the saved image. 
However, it queries the RenderWindow for the *current* size (now bigger) 
and then tries to transfer more data than what was saved, thus reading 
past the end of the BackingImage buffer.

Note that sometimes the program won't crash. If it doesn't, try resizing 
the window more rapidly several times. If the memory after the 
BackingImage buffer is valid, it will just copy garbage to the screen 
and not crash, so it all depends on the memory environment. It also does 
a real render afterwards (if it doeasn't crash) so you often don't see 
the garbage.

I tried this with VTK 4.2.2 on RedHat 8, it might not work on other 
platforms, but I think the bug is still there.

-- 
Vladan Bato
vbato at ieee.org
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