Does a png use memory equal to its size?

**Christian Knudsen** · 20-08-2009, 09:07 AM

I'm just wondering if a compressed file format such as png uses up memory equal to its size, or if it's "decompressed" before loaded into memory? I'm using OpenGL and SDL_image to open image files, by the way.

**pstudio** · 20-08-2009, 10:36 AM

At some point the png file has to be decompressed before being displayed. So yes, you'll usually only have the uncompressed data in memory.

If you didn't have to decompress the data to display it, it wouldn't actually be compressed. Then you would have found a more effective way to represent the data.

**Christian Knudsen** · 20-08-2009, 03:14 PM

That makes sense.

**noeska** · 20-08-2009, 03:49 PM

But there is also a way to use compressed textures with opengl without decompressing them. Do a search on GL_ARB_texture_compression and/or s3tc (http://www.gamedev.net/reference/pro...erpt/page2.asp)

**WILL** · 21-08-2009, 03:02 AM

PNG uses a form of LZH encoding. I've dabbled with libpng and even zlib to try and figure out how to make a simple screenshot function with it, but no luck so far.

**Christian Knudsen** · 21-08-2009, 08:54 AM

Originally Posted by noeska

But there is also a way to use compressed textures with opengl without decompressing them. Do a search on GL_ARB_texture_compression and/or s3tc (http://www.gamedev.net/reference/pro...erpt/page2.asp)

That's very interesting. I'll play around with this and see how much memory I save. Thanks!

**Christian Knudsen** · 21-08-2009, 10:35 AM

GL_COMPRESSED_RGBA doesn't seem to be supported by the current gl.pas header file. Anybody know how to add this?

EDIT: Never mind. I'm stupid.

EDIT 2: The compression creates a lot of artifacts, so I can't use it for my player sprites, but I can use it for some big and blurry background sprites. Already saved me 15 MB by just compressing them. Nice!

**User137** · 21-08-2009, 12:05 PM

You don't have to keep all textures in memory same time. Especially if its about fullscreen sized images you should load them on demand if its like more than 4 of them.

**Christian Knudsen** · 21-08-2009, 12:26 PM

They're all used all the time, so loading them on demand is not an option, as that would cause a short lag while the program reads from disk.

**noeska** · 21-08-2009, 02:41 PM

What kind of opengl unit are you using? Have a look at the delphigl site and at their dglopengl unit as that one is very complete.

Oops forgot the url: http://www.delphigl.com/