Does a png use memory equal to its size?

**Christian Knudsen** · 21-08-2009, 04:22 PM

I'm using FreePascal and their OpenGL header files. But I've got it working now - just had to use the glext.pas header file as well.

**noeska** · 21-08-2009, 05:16 PM

The compression ratio is not controlleable?
Btw it would be nice if you posted some info on how you got GL_COMPRESSED_RGBA working.

**Christian Knudsen** · 21-08-2009, 06:05 PM

Originally Posted by noeska

The compression ratio is not controlleable?
Btw it would be nice if you posted some info on how you got GL_COMPRESSED_RGBA working.

When creating your texture with glTexImage2D instead of using GL_RGBA for the internal format, just use GL_COMPRESSED_RGBA. I had a small problem with my compiler not recognizing this, but that was just because I also had to have glext.pas as a unit.

The documentation says that you can choose between a "FASTEST" and "NICEST" compression algorithm via glHint, but they seemed equally artifacty to me and the compressed textures used the same amount of memory (maybe my setup only supported the one compression algorithm - don't know).

**noeska** · 21-08-2009, 09:41 PM

Ok but should not you use glGetCompressedTexImage or is that s3tc only?

**Christian Knudsen** · 22-08-2009, 08:37 AM

As far as I understood, that's only to receive a texture from disk that has been compressed with the OpenGL compressions?

**noeska** · 22-08-2009, 09:13 AM

You know i expected GL_COMPRESSED_RBGA to work the same as s3tc, but i guess it is not.

So with GL_COMPRESSED_RGBA the texture is compressed while sending it to the videocard. And with s3tc you send an already compressed texture to the videocard.

So there is no way to use and already compressed texture with GL_COMPRESSED_RGBA .

Hmm that makes that i bit less useable in my opinion. First you have to decompres your image when loading it from disk and next let opengl compres it again when uploading it to the videocard. With s3tc you can just pass on the already compressed texture in adition to the above method with compressing it on the fly. But you get at least a speed gain uploading the textures to video ram and save some video ram.

**Christian Knudsen** · 22-08-2009, 04:31 PM

I suppose that's true. It's not really and issue for me, though, as I'm loading all the textures I'll need at the start of the "level", so I don't worry about image -> texture load times. I'm just glad that I can compress the textures in memory to save some precious video RAM.