Re: Texture size / GL_MAX_TEXTURE_SIZE ?

[Michael Diehr <md03 at xochi dot com>]

On Nov 15, 2006, at 6:46 PM, Thomas Cunningham wrote:

> > 2. Is there a list of VRAM and GL_MAX_TEXTURE_SIZE values for the
> > most common graphics cards out there?  Or, are there any "rules of
> > thumb" which would suffice?   I'm not looking for great detail, just
> > something along the lines of "pretty much every graphics chip sold
> > after 200X had at least Z total VRAM and supported NxN texture
> > sizes".   This will help me describe my "minimum systems  
> > requirements".
> http://www.opengl.org/resources/faq/technical/texture.htm
>
> See 21.130 What's the maximum size texture map my device will render
> hardware accelerated?
>
> HTH
> Thomas C.
My first tests have been of mixed success -- goal: have two 1024x1024  
textures animating with transparency, full-screen on a Powerbook  
G4/667.  This machine has a 16MB Mobility Radeon according to http:// 
mywebpages.comcast.net/macdan/pb_video.html
My naive calculations suggested this should work, i.e.:
  1024x1024x24 bit texture       =  3MB
  1024x1024x24 bit texture       =  3MB
  1152x768x24  bit screen buffer =  2.5MB
                     Grand total =  8.5MB

....and yet it was failing!   If I used two 512x512 textures it would  
work.  Where did my math go wrong?    I have some ideas:
What if all buffers are actually stored as RGBA 4 bytes instead of  
RGB 3 bytes:
  1024x1024x32 bit texture       =  4MB
  1024x1024x32 bit texture       =  4MB
  1152x768x32  bit screen buffer =  3.4MB
                     Grand total = 11.4MB

This is still well under 16MB, so perhaps something else was wrong?    
What if there are two screen buffers?
  1024x1024x32 bit texture       =  4MB
  1024x1024x32 bit texture       =  4MB
  1152x768x32  bit screen buffer =  3.4MB
  1152x768x32  bit screen buffer =  3.4MB
                     Grand total = 14.8MB

Suddenly, we are quite close to 16MB, so I can see why this may be  
failing, given overhead etc.
Further investigation of my code revealed some additional issues/ 
ideas, such as a depth buffer (which I don't need), and another  
additional buffer.    I also realized that textures can be set to use  
the 16 (15) bit RGB 555 format (GL_RGB5), which cuts their size in half.
So after a bit of tweaking I was able to get two 1024x768x32 buffers  
working on this mac.
:-)


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