I need a code (that works under OpenGL 1.5+) that checks if textures of non power of 2 are supported (via some extension maybe?)

Or maybe I should just check if OpenGL 2.0 is present and older versions would never be able to support it anyway?

Do I need to test for extension AND for OpenGL version 2.0+

OR

OpenGL 2.0+ has ARB_texture_non_power_of_two extension always present? So the check for extension presence alone is enough?

Thanks

Beware that OpenGL makes no promise to hardware-accelerate non-power-of-two textures. And you can't check for that.

In general if your GL_VERSION is 3.0 or better you're absolutely guaranteed to have them, and to have them be hardware accelerated. In the rare event that you encounter a really really really old card with a lower version, you may or may not have them be accelerated (GeForce FX was an offender here, despite claiming 2.0). You might be aware to get away with GL_ARB_texture_rectangle instead, if your usage meets it's restrictions: http://www.opengl.org/registry/specs/ARB/texture_rectangle.txt

For simplicity's sake:

[source lang="cpp"]#include <GL/glew.h>

glewInit();

if (GLEW_VERSION_2_0 || GLEW_ARB_texture_non_power_of_two)
{
/* I can haz teh supportz? */
}[/source]

OK, maybe I will explain in details.

I use glDrawPixels for 2D stuff, that are my requirements. Because it's slow I rewrote it to standard textured quads (ortho perspective, etc). But since power of two textures are sometimes not supported I need to fallback to glDrawPixels in some cases (that's why I need the detection part). I can do it any other way of course, as long as compatibility and performance is OK since this is my goal. Again, I don't need anything fancy here, it's just a replacement for glDrawPixels.

Is the GL_ARB_texture_rectangle extension significantly more supported? Or other extensions/tricks?

How to do it best? How you would do it?

OK, maybe I will explain in details.

I use glDrawPixels for 2D stuff, that are my requirements. Because it's slow I rewrote it to standard textured quads (ortho perspective, etc). But since power of two textures are sometimes not supported I need to fallback to glDrawPixels in some cases (that's why I need the detection part). I can do it any other way of course, as long as compatibility and performance is OK since this is my goal. Again, I don't need anything fancy here, it's just a replacement for glDrawPixels.

glDrawPixels can be fast if you use the right params. Since you've observed slowness I'm guessing that you're using dear old GL_RGB/GL_UNSIGNED_BYTE, which is a slow path nearly everywhere; you need these parameters to match the native format of your backbuffer otherwise GL is going to send the data through intermediate conversion steps, so try it with GL_BGRA/GL_UNSIGNED_INT_8_8_8_8_REV for starters and you should see a very noticeable performance increase (at the cost of an extra byte per pixel - fair tradeoff) - that just requires GL1.2 support. Also be sure, if you're using glDrawPixels, to switch off texturing and lighting, as OpenGL will texture and light individual pixels otherwise.

Is the GL_ARB_texture_rectangle extension significantly more supported? Or other extensions/tricks?

The definition of "significant" nowadays is that you can rely on full general non-power-of-two support being available absolutely everywhere, aside from some 6-year-old laptops or business-class PCs with integrated Intels. But since you're aiming for an extremely downlevel minimum GL_VERSION it's fair to say that GL_ARB_texture_rectangle is more likely to be supported on that class of lower paleolithic hardware.