Dear all,

I want to do rotating cube with 6 different images, i did it using traditional method of load,bind and render. But its too slow and performance is worst. I heard from the openGL experts that it can be done using texture atlast method and uv mapping. I am a newbie to openGL programming . Can any one explain how to do this,if you can share the code related to it it would be great.

Thanks in advance for the help.

Regards
Girish

Hi,
First, if you are displaying a single simple rotating cube with 6 textures and it's slow, maybe the problem is elsewhere. Of course, this depends on what phone you're using, but event on my G1, I can run this kind of rendering without problems. So maybe you should try to profile your code.

Anyway, to answer your question. A texture atlas is something like this :
http://www.larabie.net/ogre/CombinedTextures.jpg

Basically it's a big texture that contains 4 (or whatever number you like) other textures. So you reduce the number of textures you have. Now, if you want to render a quad with the grass texture, the 4 vertices would have the following texture coordinates :

Code: Select all

top-left : (0,1)
top-right: (0.5, 1);
bottom-right: (0.5, 0.5);
bottom-left: (0, 0.5);


So you're taking only a quarter of the actual texture, the quarter that correspond to the grass.

Ok, so that's the idea. Unfortunately, I don't have code to do that, but a search for "texture atlas opengl" on Google should make you happy.
You might want to look at this thread which has some code.
Also, [url=http://developer.apple.com/library/ios/#samplecode/GLTextureAtlas/Listings/ReadMe_txt.html#//apple_ref/doc/uid/DTS40009014-ReadMe_txt-DontLinkElementID_11]here[/url] is an example for the iPhone (the ideas are the same).