OpenGL texture tilted

Question

When I load a texture in OpenGL and this has one (GL_ALPHA) or three components per pixel (GL_RGB), the texture appears tilted. What makes this happen?

As additional detail, the relation width/height seems to affect. For example, an image of 1366x768(683/384) appears tilted while an image of 1920x1080(16/9) is mapped correctly.

Answer 1

This is probably a padding/alignment issue.

GL, by default, expects rows of pixels to be padded to a multiple of 4 bytes. A 1366 wide texture with 1 byte or 3 byte wide pixels, will not be naturally 4 byte aligned.

Possible fixes for this are:

• Tell GL how your texture is packed, using (for example) glPixelStorei(GL_UNPACK_ALIGNMENT, 1);
• Change the dimensions of your texture, such that the padding matches without changing anything
• Change the loading of your texture, such that the padding is consistent with what GL expects