Swift - How to draw a line in OpenGL ES?

Question

I am trying to draw a black single row on a GLKitView using Swift , but this will not work. I can clear the screen, and I can fill it with any color, but I can't draw anything on it. And I know this question has been asked many times, but I could not find the answer to Swift. Moreover, there is no information about using OpenGL ES with Swift, so I came here.

Here is my code:

 import GLKit class MyGLKit: GLKView { override func drawRect(rect: CGRect) { glClearColor(0.8, 0.8, 0.8, 1.0) glClear(GLbitfield(GL_COLOR_BUFFER_BIT)) glColor4f(0, 0, 0, 1) var line: [GLfloat] = [-1, 0, 1, 0] var len = line.count * sizeof(GLfloat) // Create an handle for a buffer object array var bufferObjectNameArray: GLuint = 0 // Have OpenGL generate a buffer name and store it in the buffer object array glGenBuffers(1, &bufferObjectNameArray); // Bind the buffer object array to the GL_ARRAY_BUFFER target buffer glBindBuffer(GLbitfield(GL_ARRAY_BUFFER), bufferObjectNameArray); // Send the line data over to the target buffer in GPU RAM glBufferData( GLbitfield(GL_ARRAY_BUFFER), // the target buffer len, // the number of bytes to put into the buffer line, // a pointer to the data being copied GLbitfield(GL_STATIC_DRAW)); // the usage pattern of the data glVertexPointer(2, GLbitfield(GL_FLOAT), 0, line); var programHandle: GLuint = glCreateProgram() glLinkProgram(programHandle) glDrawArrays(GLbitfield(GL_LINES), 0, 2); } } 

I'm not sure what this code does, because OpenGL ES seems insane after regular OpenGL. I mean, you need to write a lot of code to draw a single line. Why does it work?

Answer 1

I did not use Swift, but based on the code in OpenGL EXC_BAD_ACCESS when calling glDrawElements in Swift, but not in Objective-C , your glVertexPointer() call should look like this: this:

 let bufferOffset: CConstVoidPointer = COpaquePointer(UnsafePointer<Int>(0)) glVertexPointer(2, GLbitfield(GL_FLOAT), 0, bufferOffset); 

It also looks like you are not creating a shader program:

 var programHandle: GLuint = glCreateProgram() glLinkProgram(programHandle) 

There are tons of things you need to go through between you if you use simple OpenGL. You need to create shader objects, give them code written in GLSL, make calls to compile shaders, etc. I believe that GLKit has functionality for using pre-baked shaders.

As for why OpenGL is so “crazy" that it goes beyond the scope of this site. And very subjective. IMHO, the main thing to keep in mind is that OpenGL is not intended to be used as a convenient API for programmers. It is designed to provide a relatively fine general abstraction for access to graphics hardware. And the trend towards comparable APIs is to make the abstraction layer even thinner to reduce overhead (see, for example, DirectX 12).

Nothing prevents anyone from implementing more convenient higher-level APIs on top of OpenGL. These interfaces exist, and people use them.