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Johnnie
04-27-2010, 09:53 AM
Hi,

Say for example I have a Back-Buffer the size of 2000x1000.

In addition I have a render target (FBO) the size of 2000x1000.

And say the Back-Buffer is multi-sampled (16).

I want to blit the pixels from the back-buffer to the final render target, BUT - I want to copy the entire back-buffer frame to the upper-left quarter of the final render target.

Meaning - I want to copy from the BB and shrink it by 4 when it's copied to the final render target.

The problem is - this doesn't work and gives me an 'Invalid Operation' error.


So what I did to bypass the error is -

I've rendered to the 2000x1000 Back-buffer.

Then I copied the pixels as they are to a TEMP render target 2000x1000 size.

Then I copied & shrunk from the TEMP render target to the FINAL render target, and this works.


Maybe you can't copy & shrink from the Multi-Sampled Back-Buffer to a non-multi-sampled final render target ?

Is this true ?

If not - I'd be happy to hear so ...

Because this extra copy through the TEMP render target causes me some performance issues I cannot afford ...

Thank you all in advance !

strattonbrazil
04-27-2010, 11:05 AM
It is possible according to the blit command. You might have some kind of mismatch in types and targets.

http://www.opengl.org/registry/specs/EXT/framebuffer_blit.txt



If the source and destination rectangle dimensions do not match,
the source image is stretched to fit the destination
rectangle. <filter> must be LINEAR or NEAREST and specifies the
method of interpolation to be applied if the image is
stretched. LINEAR filtering is allowed only for the color buffer;
if <mask> includes DEPTH_BUFFER_BIT or STENCIL_BUFFER_BIT, and
filter is not NEAREST, no copy is performed and an
INVALID_OPERATION error is generated. If the source and
destination dimensions are identical, no filtering is applied. If
either the source or destination rectangle specifies a negative
dimension, the image is reversed in the corresponding direction.
If both the source and destination rectangles specify a negative
dimension for the same direction, no reversal is performed.

Johnnie
04-27-2010, 06:39 PM
There is no mention to the fact that the Back-Buffer is MULTI-SAMPLED, and the render target to which I want to copy is NOT MULTI-SAMPLED.

Could that be what causes me the INVALID OPERATION ?

strattonbrazil
04-29-2010, 02:49 PM
No, blitting should take care of that. Here's a working example I use as reference. You can always try swapping in his values.

http://blog.dexta.ch/2008/08/27/gl_ext_framebuffer_object-
with-multisampling/