使用Swift Package Manager时出错

Question

I'm following this tutorial on using OpenGL in Swift. It apparently depends on some GitHub Repo for GLFW and uses a Package.swift file to build it into your executable. Sadly, while running the instructed build command swift build -Xcc -I/usr/local/include -Xlinker -L/usr/local/lib I get the following error:

error: Empty manifest file is not supported anymore. Use swift package init to autogenerate.

When I run the suggested init command, I get:

error: a manifest file already exists in this directory

What should I do?

Answer 1

That tutorial is written for Swift version 2, and it's been outdated for some time. The only reason you need the library in that repository is because it defines some OpenGL function loaders necessary to make your program link properly. I currently use a patched version of that SGLOpenGL library that I hacked to make it compile under Swift 3. I believe this is the only way currently to use OpenGL with Swift. You will have to correct the Swift UnsafePointer s and rewrite the function parameter lists to use (or remove) named arguments, among other things, as Swift 3 was a source-breaking release. The compiler will generally tell you what you have to do, it's just a lot of tedious work.

Note that you don't need any of Turnbull's other libraries to use OpenGL with Swift. You can easily (“easily”) write your own implementations of the Math functions for the quaternions, vectors, matrices, camera frusta, etc. Google is your friend, as most of these routines are well-studied problems in computer graphics, and there is a great deal of pseudocode and C++ implementations on the web to help you get started.

The Image PNG library is non-trivial to replace, but luckily there already exists a native Swift PNG decoder MaxPNG ^† designed to work with graphics frameworks.

Good luck!!!

^† ( Disclosure, I am the author of MaxPNG ; I wrote it because I was in the exact same position as you a few months ago. )