Porting the game engine from OpenGL to Metal

If you are not aware of, Apple came out with its own graphics library; similar to OpenGL, a couple of years ago. The name of this graphics library is Metal.

When Metal came out, I had barely finished the first stage of my game engine. Back then, I thought that it would be a good idea to port the engine to Metal. However, I resisted in doing so, until Metal became stable.

Well, on the weekend of July 4th, 2017, I happened to play around with some Metal demo apps, and I was impressed at Metal's power. It was then that I decided to use my four-day weekend learning and porting the engine from OpenGL to Metal.

And so I did.

I spent Saturday morning to Tuesday night learning Metal in depth. I didn't even go out at all during those four days. I was focused and excited to learn about Metal.

On Tuesday night, I laid out a plan on how to port the engine from OpenGL to Metal. All in all, the porting took about two weeks. There are some minor bugs to fix, but all in all, I'm pleased with the results. Here is a screenshot of the engine using Metal.

Engine using Metal

Engine using Metal


So what did I learn?

Most of what I know about Metal, you can find it here. I wrote these articles a while ago,; I used them as a reference during my review and the porting. But here are the main things that you should know about Metal:

  • Metal is not as convoluted as OpenGL. Metal is clean and has the concept of Objects. You can think of it as an Object-Oriented language, but for graphics. It is amazing to work with. Seriously.
  • Metal is less forgiving than OpenGL. During the porting, I noticed many incorrect Computer Graphics implementation done in the engine. At first, I thought that the issue was with Metal but then realized that I had made several mistakes using OpenGL. OpenGL did not make a big deal about it, but Metal did mind and kept spitting out error messages. For example, I had incorrectly implemented certain aspects of Normal Mapping, Shadows, and Vertex-Skinning.
  • The Perspective and Orthogonal projection matrices you use in OpenGL based games will not work on Metal. You need to compute a different projection matrix for Metal. The reason is that Metal uses a different coordinate system than OpenGL. I will write more about this issue later. However, if you need an example of these matrices, send me a message, and I'll provide you with one.

It is amazingly simple to work with Metal. However, since there are not plenty of tutorials out there, it may be hard for a newbie to get Metal working.

If you have experience working with OpenGL and have a good grasp of computer graphics, Metal will be a piece of cake to learn. I can guarantee that you will love it. However, if you are a newbie, keep in mind, that it may take a while for you to grasp Computer Graphics concepts and Metal at the same time. Hopefully, these articles can help you out.

Thanks for reading.

Harold Serrano

Computer Graphics Enthusiast. Currently developing a 3D Game Engine.