You'll also want to make sure you've got the Xcode Command Line Tools Package installed; run xcode-select --install and you'll be good to go. A quick aside: the last time I touched OpenGL was probably around , maybe early Instead I used CreateWindow and wglCreateContext and a shitload of other boilerplate to create a window and rendering context, switch statements that approached several hundred lines inside a good old fashioned WindowProc for handling input, and I don't think I even had a graphics card capable of using anything past OpenGL 1.
All that is to say, when I started reading up on OpenGL again I was kind of confused by the purpose of these libraries. If you've actually been keeping up with OpenGL for the last eleven or twelve years then they're probably not so mysterious. But if you're way out of the loop or totally new to this I think I can shed some light on them and hopefully explain in a convincing way why you'd want to use them.
You can skip ahead if this is all familiar territory for you. It wasn't for me so I'm going to provide a brief synopsis of each. Let's start with GLEW. OpenGL, like most standards and specifications, is an ongoing and living thing. Since it is fundamentally tied to its implimentation and the underlying graphics hardware, care has been taken to introduce new features in a controlled manner.
An Introduction on OpenGL with 2D Graphics
This is done through extensions which allow hardware vendors to implement and expose particular features independently. One fairly large downside to the way extensions are implemented is that each extension function's location has to be determined at run time. For this calls to dlopen and dlsym are necessary or if you're on Windows: wglGetProcAddress. Doing this for every extension function you intend to call is obviously less than ideal. You might wonder, "Is this really necessary? However the type of boilerplate it focuses on is entirely different.
Before you can actually start using OpenGL you need a rendering context. To get a rendering context you need a surface or window to render to. It should go without saying that creating a window is extremely platform dependent. Even when you're targeting just one platform the process can be laborious. As an added bonus GLFW also normalizes the process of dealing with multiple monitors and handling input. I'm usually a big believer in DIY, but unless you've got a really good reason you should probably let GLFW or a similar library handle the details of this kind of highly platform specific initialization.
If you're curious you will definitely learn something useful by creating windows and handling input without help, but either can be a very deep rabbit hole if you're not careful. You'll sometimes see tutorials tell you to create a Command Line Tool project. It turns out this is a non-issue. There's one very important reason to not go that route though. Creating a Cocoa Application allows you to easily bundle files with the actual executable in a.
I'm sure there's a way to coax Command Line Tool projects into doing that, but it's much easier to just start off with a Cocoa Application that's already set up with that in mind. Click "Next" again and then choose a location for your project. Click "Create" when finished.
Close the window and open up a terminal and cd into the project directory.
OpenGL ES vs. Metal
Do a git status now to confirm everything is as it should be. There should be a directory waiting to be added and commited, but you don't really want to include that with the project. Copy this for the contents of a. After creating the. Back in Xcode go ahead and select the test product and delete it unless you really want to keep it.
This is why you don't care if Xcode only lets you select between Switft and Objective-C. You might also want to add in some sort of simple "Hello, world! Build and run the project just to make sure everything is working. You should see your output below in the debug area. You may be wondering now, "Why is this guy telling me when to commit?
I'm a grown up, I can commit when I want to. But during this process of figuring all of this out I found there were several points to which I reverted at least once. I hope that by explicitly calling out when those points are I'll save you some trouble later on. Now that you're not working with a normal Cocoa application anymore there's a few files you don't need.
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Specifically: AppDelegate. Highlight them Commit the changes, and if you feel like it, build and run the project again just to make sure all is well. These next couple of steps aren't necessary in the slightest. In fact, for a small demo project they're pointless. But I'm going to assume that maybe someday this project will become larger, more complicated, and have many many source files.
To make that eventuality less of a nightmare create a directory named src or whatever you want really and then move your main. Xcode will now be confused. Don't worry. You can fix it. Create a group under your project named "src" or whatever you named the directory from before. Highlight main. Then click the little folder icon to browse for the file. Select it and click "Choose". The file should no longer appear red and Xcode should now be unconfused. Once again it's a great time to build and run the project to make sure nothing is broken and commit your changes.
Finally it's time to start doing something actually related to OpenGL. Sort of. We bind it, to bring it in to focus in the state machine. This lets us enable the first attribute; 0. We are only using a single vertex buffer, so we know that it will be attribute location 0.nn.threadsol.com/11157-mobile-phone.php
SDLTutorials - SDL Wiki'
The glVertexAttribPointer function defines the layout of our first vertex buffer; "0" means define the layout for attribute number 0. You will see that the attribute pointer from the VAO will match up to our input variables in the shader. This shader programme is made from the minimum 2 parts; a vertex shader , which describes where the 3d points should end up on the display, and a fragment shader which colours the surfaces. Both are be written in plain text, and look a lot like C programmes. Loading these from plain-text files would be nicer; I just wanted to save a bit of web real-estate by hard-coding them here.
The first line says which version of the shading language to use; in this case 4.
Moving from OpenGL to Metal
If you're limited to OpenGL 3 , change the first line from "" to ""; the version of the shading language compatible with OpenGL 3. My vertex shader has 1 input variable; a vec3 vector made from 3 floats , which matches up to our VAO's attribute pointer. This means that each vertex shader gets 3 of the 9 floats from our buffer - therefore 3 vertex shaders will run concurrently; each one positioning 1 of the vertices.
You can see that I haven't modified this at all, just added a 1 to the 4th component. The 1 at the end just means "don't calculate any perspective". Again, you may need to change the first line of the fragment shader if you are on OpenGL 3. My fragment shader will run once per pixel-sized fragment that the surface of the shape covers. We still haven't told GL that it will be a triangle it could be 2 lines. You can guess that for a triangle, we will have lots more fragment shaders running than vertex shaders for this shape. The fragment shader has one job - setting the colour of each fragment.
It therefore has 1 output - a 4d vector representing a colour made from red, blue, green, and alpha components - each component has a value between 0 and 1.
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We aren't using the alpha component. Can you guess what colour this is?
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