[SDL] 2D with openGL & SDL

[benang at cs.its.ac.id]

Yeah, it's a VIA Unichrome. According to what you said, this card is
probably a low-end one, right? I am having a second thought about this
now.  Maybe I won't implement openGL to the current game, but I will still
try to redesign my rendering engine using openGL. I want to see how it
turns out. Thanks.

Matthias Weigand said:
>
> Mike Powell wrote:
>> benang at cs.its.ac.id wrote:
>>
>>> 1. Performance wise, will this make my application faster or slower?
>>> FYI,
>>> the intended machine is a VIA EPIA Mini ITX embedded with Linux
>>> openSuSE
>>> 10.1 as the OS.
>>>
>>
>> On this point I'm really not sure, but I would guess that, so long as
>> you have a good graphics card, and you keep the sprites in video RAM as
>> textures, it'll probably be faster. Plus, certain types of operations,
>> such as scaling or rotating sprites, will be much faster.
>>
>>
> I think your graphics chip is a VIA Unichrome Pro. For usual
> applications the 3D functionality of this chip will be faster. As Mike
> said, rotation and scaling is for free. But i've encountered some limits
> with this chip:
> lines and points rendered with opengl were very slow on this chip
> (glBegin(GL_LINES)). If you need to draw lines, you should render a thin
> quad.
> Also i wasn't able to make use of the multitexture feature, although the
> chip exposes the appropriate extension. Same code worked on every other
> graphics card. If you have to do complex blendings you might have to do
> it by several steps (like you would do now).
> But this may have been fixed with new driver versions.
>
>>> 2. Do I need to implement shader languages (I think maybe Cg)?
>>>
>>
>> Not unless you want to do some pretty fancy special effects. If your
>> game is based entirely on drawing 2D images on top of each other with
>> alpha channels, then just use OpenGL's standard blending modes and
>> you'll be fine.
>>
>>
> In case of the VIA Unichrome you won't be able to do that, since the
> chip doesn't support any shading language. Maybe Unichrome Pro does.
>>> 3. What's the settings for openGL so that the 2D environment looked
>>> just
>>> like when I blit it directly to an SDL Surface (eg, the viewport, 1
>>> points
>>> equals to 1 pixel, etc)?
>>>
>>
>> Leave the viewport alone unless you actually want to restrict drawing to
>> limited portion of the screen. The standard state of the viewport is the
>> same as the screen/window that the game is drawn into.
>>
>> For setting it up to have 1 point per pixel, gluOrtho2D() is your
>> friend. Specifically:
>>
>> glMatrixMode(GL_PROJECTION);
>> glLoadIdentity();
>> gluOrtho2D(0, width, 0, height);
>>
>> Where "width" and "height" are the screen resolution.
>>
>> Note that OpenGL's coordinate system is based in the lower-left corner,
>> not the upper-left corner like you might be used to. I BELIEVE the the
>> call to gluOrtho2D, as I just demonstrated, will flip it vertically so
>> it will map to what you expect. However, no promises on that. If that
>> doesn't work, you can always use the modelview matrix to scale
>> everything by -1.0 on the y axis.
>>
>>
>>> 4. AFAIK, to add a texture, the width & height of the image should be a
>>> power of 2. So how do I make a sprite with width and/or height not of
>>> power of 2?
>>>
>>
>> This was true in the old versions of OpenGL, but I know it's been fixed
>> by OpenGL 2.0. Not sure, offhand, exactly which version made the shift,
>> but if your version is up to date, you should be able to use any texture
>> size. Provided, of course, it's not larger then your implementation's
>> maximum texture size. These days, that's usually either 512 or 1024, so
>> you probably won't have a problem there.
>>
> Again, the onboard graphics card might be far away from OpenGL 2.0. I
> suggest to look for the extensions provided by your graphics chip. For
> the use of non-power-of-two-textures OpenGL 2.0 would be great, but the
> extension GL_ARB_texture_rectangle supports it, too (less comfortable
> and minor limits). I think the Unichrome chip doesn't support any of
> these. So you have to preprocess images by yourself or let gluScaleImage
> do it for you on the fly.
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Fare thee well,
Bawenang R. P. P.

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