Re: Rotating texture with even dimensions by 90 degree

Hi,

Maybe you are hitting this bug:
https://bugzilla.libsdl.org/show_bug.cgi?id=2421
I have just added a test-case for rotations 0 / 90 / 180 / 270.

It fails for the "software" renderer with sometimes: offset, or image
truncation.
But it works for opengl, opengles and opengles2 renderers.

I haven't tested it with windows direct3d ... If you're on windows, you may
want to try a patch including in this bug.

Hope it helps,
Sylvain








On 7 August 2016 at 13:48, David Olofson <[email protected]> wrote:

> My guess is that you're pretty much the only one using that feature
> with a pixel precision requirement at this point. (I'm not using it in
> Kobo Redux, for example, because rotating sprites and tiles breaks any
> any directional lighting the art may have.)
>
> It may also be that the problem only occurs on certain platforms or
> drivers.
>
> Anyway, when dealing with a 3D API, you typically have to take the
> size of pixels and texels in account, and more specifically, make sure
> your texel filters hit the center of pixels, rather than one of the
> corners. With filtering (biliniar or similar), it's not all that
> critical, but with "nearest", even the slightest rounding error in the
> wrong direction means you get the wrong texel. A "2D" API built over a
> 3D API, like the SDL one, is supposed to take care of this internally,
> as it's generally not accessible through such an API.
>
> So, I suspect it's a rounding error in the transform, and either SDL
> isn't taking that in account, or it only happens in certain
> environments. Have you tried using other SDL renderers (OpenGL, D3D,
> software...), or running it on a different OS, or just another
> computer, to see if the problem is still there?
>
> On Mon, Aug 1, 2016 at 2:28 AM, stewambo <[email protected]> wrote:
> > Still no answers? I thought there were even some devs of SDL here?
> > In the meantime i used a dirtly hack that just shifted the rotated
> textures
> > back by one pixel, but when combining the rotation witn a scaling
> operation
> > the problem is even worse, so help is still highly appreciated...
> >
> > _______________________________________________
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> >
>
>
>
> --
> //David Olofson - Consultant, Developer, Artist, Open Source Advocate
>
> .--- Games, examples, libraries, scripting, sound, music, graphics ---.
> |   http://consulting.olofson.net          http://olofsonarcade.com   |
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-- 
Sylvain Becker

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