Re: [gl4java-usergroup] Drawing to an offscreen buffer silently

[Pepijn V. E. <pep...@lu...>]

I've never used auxilary buffers so I can't comment on that. But
wouldn't it be easier to just render on the back buffer as usual, but
not perform a buffer swap?

Pepijn

Alban Cousinie wrote:
> Hi,
> 
> When I ask gl4java the count of available auxiliary buffers, 
> It returns 0.
> 
> gl.glGetIntegerv(gl.GL_AUX_BUFFERS, numbuff);
> 
> Does anyone know if auxiliary buffers are activated by default, if they
> can be activated, or if I get 0 buffers because my OpenGL implementation
> (nvidia, win32) would not support auxiliary buffers ?
> 
> I'm implementing color picking. It's done, it works, but my screen
> flashes (a tenth of second, showing my drawn colors) because it looks
> like it is drawing on a buffer used by OpenGL for display, though I'm
> drawing my objects into the left buffer (because I don't have any
> auxiliary buffers).
> 
> Here is the code (a bit simplified for ease of reading):
> 
> //switch to an offscreen buffer. Left buffer should be 
> //available in any implementation since it is mandatory 
> gl.glDrawBuffer(gl.GL_LEFT);
> gl.glReadBuffer(gl.GL_LEFT);
> //make sure the buffer can be written
> gl.glColorMask(true,true,true,true);
>             
> //clean the buffer
> gl.glClear(gl.GL_COLOR_BUFFER_BIT);
> 
> //draw our objects in plain red color
> drawObjects();
> 
> //look for color under the mouse             
> gl.glReadPixels(nextX,canvasSize().height-yMouseCoordinate,1,1,gl.GL_RED
> ,gl.GL_UNSIGNED_BYTE,pickedColor);
>             
> processPickedColorAndTellMeWhatObjectHasBeenPicked(pickedColor);
>             
> //switch back to regular display buffer 
> gl.glReadBuffer(gl.GL_BACK);
> gl.glDrawBuffer(gl.GL_BACK);
> 
> 
> Anyone has an idea of what could go wrong with those buffers ?
> 
> Thanks,
> 
> Alban Cousinié
> 
> MIND2MACHINE
> http://www.mind2machine.com
>  
> 
> 
> 
> 
> 
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