[SDL] Mirror blitting with SDL

David Olofson david at olofson.net
Sat Nov 22 07:47:00 PST 2003


On Saturday 22 November 2003 16.02, E$h wrote:
> Hello!
> DirectDraw can do mirror blitting of an image (with flags
> DDBLTFX_MIRRORLEFTRIGHT and DDBLTFX_MIRRORUPDOWN). I need same
> feature for my SDL program under Linux. As far as I know there are
> no such tool in SDL library for doing this. So, how can I implement
> this feature? Is there any libraries or sample code?
> Thank you very much in advance.

For maximum performance on all backends, this would have to be 
implemented in SDL, rather than in an add-on library. One reason to 
add this to SDL is that you can take advantage of DirectX, OpenGL 
[glSDL] and other targets that can do this in hardware. Another 
reason would be that SDL's s/w blitters could probably be made to do 
this without much overhead. In both cases, having this feature would 
eliminate the need for doing the flipping at load/init time, or on 
the fly into temporary surfaces.

Then again, one reason *not* to bother with this would be that there 
is really little need for it in "real" applications. Most modern 
games have rendered or hand drawn graphics with a "lightsourced" 3D 
look, meaning that you can't flip it without ruining the appearance.

The only really useful solution would include free rotation along with 
bumpmapping, and that's probably better left to custom (ie 
specialised, highly optimised) blitting code, OpenGL or Direct3D. (As 
opposed to pretty much all other targets, OpenGL and Direct3D can 
accelerate both rotation and bumpmapping.)


//David Olofson - Programmer, Composer, Open Source Advocate

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