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OpenGL power of 2 texture dimensions

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I've been working with graphics API's such as openGL and Direct3D for about a year now and a question has been hovering over my head for sometime that I'd like to have answered. Both API's, when dealing with textures, have this constraint that the textures dimensions must be powers of 2. I also know that direct3D has some flags that all you to overriden this behavior. My question is why don't they just always allow non-power of 2 textures? The texts that I have read never really explained this constraint and I have always just convinced myself that it has something to do with performance. Can anyone offer anymore insight into the significance of this constraint and what the consequences would be of using non-power of 2 textures? thanks,

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The power-of-2 constraint isn't an API constraint. As far as OGL and DX are concerned, using non-power-of-2 textures would be fine.

It's the actual hardware that has this constraint. I'm not sure of the exact technical reason why, but I would estimate this had to do with doing texture lookups on the GPU.

I'm not sure if you are aware, but most of todays hardware does support non-power-of-2 textures (I'm sure all SM3 cards do). This just isn't too popular yet cause old cards don't support it. I suppose in a while this would no longer be an issue.

Hope this helps.

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Non-power-of-2-textures isn't a feature that you can toggle on and off - rather, it is a feature that is or isn't supported by the hardware. Older hardware (pre-GeForce4 IIRC) doesn't support it, simply because it wasn't available at that point in time. It doesn't really have to do with performance - just what can and can't be done based on your hardware.

To determine if you can use non-pow-2-textures in D3D, just check the D3DCAPS9.TextureCaps member.

Edit: Whoa, beaten to it [grin]

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