ATI compressed texture formats & auto-compression

[Hamish]

Next silly question time...

In my OpenGL SUperBible, there's a section on compressed textures. According 
to the code in there you can get the hardware to compress a texture when 
loading it... But I can't seem to get a sane response from OpenGL when I'm 
doing it...

Using 

    glGetIntegerv(GL_NUM_COMPRESSED_TEXTURE_FORMATS_ARB, 
&num_compressed_format);


I get back 0 for num_compressed_format. But glxinfo seems to indicate that 
compressed formats ARE available... Trying to load the textures using

  glTexImage2D(GL_TEXTURE_2D, 0, GL_TEXTURE_COMPRESSED_ARB, width, height, 0, 
GL_RGB, GL_UNSIGNED_BYTE, image);


fails too... Indicated by 

    glGetTexLevelParameteriv(GL_TEXTURE_2D, 0, GL_TEXTURE_COMPRESSED_ARB, 
&compressed);


returning 0 in compressed.

glxinfo says

GL_ARB_texture_compression is supported... So why don't I get a value besides 
0 when getting GL_NUM_COMPRESSED_TEXTURE_FORMATS_ARB? Or am I looking in the 
wrong place and the open driver doesn't actually support any compressed 
textures?

TIA
  Hamish.
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