| Re: [AD] OpenGL and upside down |
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- To: Coordination of admins/developers of the game programming library Allegro <alleg-developers@xxxxxxxxxx>
- Subject: Re: [AD] OpenGL and upside down
- From: Elias Pschernig <elias@xxxxxxxxxx>
- Date: Tue, 18 Mar 2008 03:18:05 +0100
On Sat, 2008-03-15 at 15:51 +0000, Peter Hull wrote:
> If you lock the OpenGL back-buffer, it currently reads the pixels and
> then reverses the order of the rows (because OpenGL bitmaps start from
> the bottom up and Allegro start from the top down). When you unlock,
> the opposite process occurs. This reversing is done by a load of
> memcpy-ing.
>
> Would it be possible to avoid this by returning a locked region with
> data pointing to the last row of the region but with a negative pitch?
>
I tried doing just that at first, but it did not work. Either because I
did it wrong, or because my version of the Nvidia drivers is broken and
supports only positive pitch.
But, it's not a big issue, since usually you will always prefer FBOs
over the memory locking.
--
Elias Pschernig <elias@xxxxxxxxxx>