Coordinate Systems

Epiar uses a pseudo-2D OpenGL context (source:/Graphics/video.cpp#L129) which does not obey Coordinate I signedness ((0,0) would be in the lower-left with increasing x going right and increasing y going up). However, we use SDL for many things, including image loading, and it appears that SDL stores images backwards, making it easiest (and the ​NeHe tutorials do it this following way too) to set up OpenGL to emulate an old style video buffer coordinate system, where (0,0) is in the top-left, x increases to the right and y increases down. If you call Image::Draw(x,y), it will draw the image so that the upper-left of the image is at (x,y). There is also a Image::DrawCentered(x,y), in which the center of the image would then be located at (x,y).

There's no speed disadvantage to this, you just have to keep it in my when using coordinates at all, especially when you're writing an algorithm that uses trigonometry.