which better directx or opengl

DirectX is not for graphics. Direct3D is the DirectX component for graphics. You can use DirectX and OpenGL together by using DirectX for everything non-graphical and OpenGL for the graphics.

People are often curious about whether Direct3D or OpenGL is better. They're both similarly functional and similarly fast, similarly easy, so really there's no great difference between them.

However,Direct3D will only be available on Windows platforms (Win2K, WinXP, XBox, etc.). And, OpenGL is avaliable EVERYWHERE (all Windows platforms, Mac, Linux, Playstation, Wii, etc.).

So if you're only writing for Windows platforms, doesn't really matter which. Otherwise, go OpenGL. Moreover, OpenGL is easier for beginners and more portable.

For more information,visit Comparison of OpenGL and Direct3D[^]