问题
I have discovered that there are still a fair number of drivers out there that don't support NPOT textures so I'm trying to retro-fit my 2D engine (based on OpenTK, which is in turn based on OpenGL) with Texture2D support instead of relying on GL_ARB_texture_rectangle. As part of this I am forcing all NPOTS texture bitmaps to allocate extra space up to the next power-of-2 size so they won't cause errors on these drivers. My question is, do I really have to resize the real bitmap and texture and allocate all that extra memory, or is there a way to tell OpenGL that I want a power-of-2 size texture, but I'm only going to use a portion of it in the upper left?
Right now my call looks like this:
GL.TexImage2D(texTarget, 0, PixelInternalFormat.Rgba8, bmpUse.Width, bmpUse.Height, 0, PixelFormat.Bgra, PixelType.UnsignedByte, bits.Scan0);
This is after I have made bmpUse be a copy of my real texture bitmap with extra space on the right and bottom.
回答1:
Use glTexImage2D with empty data to initialize the texture and glTexSubImage2D to fill a portion of it with data. Technically OpenGL allows the data parameter given to glTexImage{1,2,3}D to be a null pointer, indicating that the texture object is just to be initializd. It depends on the language binding, if that feature remains supported in the target language – just test what happens if you pass a null pointer.
回答2:
datenwolf is right on how to initialize the texture with just a partial image, but there are 2 issues with this you need to be aware of:
- you need to remap the texture coordinates of your mesh, as the [0-1] texture range of the full texture now also contains uninitialized data, as opposed to your full texture. The useful range is now
[0-orig_width/padded_width] - wrapping of your texture will only wrap the whole texture, not your sub-part.
来源：https://stackoverflow.com/questions/5073611/possible-to-glteximage2d-an-npot-image-onto-a-pow-2-texture-without-extra-alloca