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I understood why my code did not work with rectangle textures :</p>

  • from Cg, rectangle textures lookups are done using the texRECT function, instead of tex2D
  • the GL_TEXTURE_RECTANGLE_ARB extension specifications make it clear that rectangle textures coordinates are absolute (in pixels) and not relative, unlike those for textures defined with GL_TEXTURE_2D…

There was also a problem in my textures, even though it did not prevent anything to seem to work fine :

I was storing them in the GL_RGBA format, which stores single byte values for each channel of each pixel. Doing floating-point computing obviously required floating point results, so I switched my textures format to GL_RGBA32F_ARB… Just another extension needed by my stuff…</p>

And I managed to slow Mac OS X down like a dog, when running my cascaded filters at maximum speed with lots of fragment shaders switches (and big code size, almost the maximal amount allowed for my poor GeForce FX Go500…).</p>


– take a look at Brook seriously</p>