Question

So im trying to create an openGL view (in my window). Im making a Cocoa app.
Ive managed to create one through Interface Builder, but for educational purposes i want to go on and make one without it. Just on papers.

And here is the point im telling you im struggling with it.
So what ive basically done-tried so far is this:
I ve created a new class “MyOpenGLView.h/m” inheriting from NSOpenGLView.
I ve added no private vars or methods to it just the class name. The only thing i did, was override initWithFrame: (adding a self = [super initWithFrame:pixelFormat:] inside it.)
I read about it on the Web that you have to instantiate it with something like this first before you can use it). here is the code:

- (id) initWithFrame:(NSRect)frameRect
{
 NSOpenGLPixelFormat *pixelFormat = [[NSOpenGLPixelFormat alloc]
                                    initWithAttributes:(NSOpenGLPixelFormatAttribute[])
                                    {
                                    NSOpenGLPFAWindow,
                                    NSOpenGLPFADoubleBuffer,
                                    NSOpenGLPFADepthSize, 32,
                                    nil
                                    }];
 self = [super initWithFrame:frameRect pixelFormat:pixelFormat];
 [[self openGLContext] makeCurrentContext];
}

So i have another class named by “MyViewController.h/m” which handles my View?
and there i have my MyOpenGLView *myView.
In the .m file i go with something like this:

myView = [[MyOpenGLView alloc] initWithFrame:CGRectMake(0,0,100.0,100.0)];
if (!myView) { NSLog(@"ERROR"); }

and of course, i get error.

There is no openGL view ported in my window application. I would guess its something about the hierarchy on methods being called but then again.. im not sure. Can you aid me with it?

Answer 1

They way I have gotten this to work is I don’t implement an init method in my view. Then in my controller or app delegate I have.

@implementation AppDelegate

@synthesize window = _window;
@synthesize view = _view;

- (void)applicationDidFinishLaunching:(NSNotification *)aNotification {
    NSRect mainDisplayRect = [[NSScreen mainScreen] frame]; // I'm going to make a full screen view.

    NSOpenGLPixelFormatAttribute attr[] = {
        NSOpenGLPFAOpenGLProfile, NSOpenGLProfileVersion3_2Core, // Needed if using opengl 3.2 you can comment this line out to use the old version.
        NSOpenGLPFAColorSize,     24,
        NSOpenGLPFAAlphaSize,     8,
        NSOpenGLPFAAccelerated,
        NSOpenGLPFADoubleBuffer,
        0
    };

    NSOpenGLPixelFormat *pix = [[NSOpenGLPixelFormat alloc] initWithAttributes:attr];
    self.view = [[OpenGLViewCoreProfile alloc] initWithFrame:mainDisplayRect pixelFormat:pix];

    // Below shows how to make the view fullscreen. But you could just add to the contact view of any window.
    self.window = [[NSWindow alloc] initWithContentRect:mainDisplayRect
                                              styleMask:NSBorderlessWindowMask 
                                                backing:NSBackingStoreBuffered 
                                                  defer:YES];

    self.window.opaque = YES;
    self.window.hidesOnDeactivate = YES;
    self.window.level = NSMainMenuWindowLevel + 1; // Show window above main menu.
    self.window.contentView = self.view;
    [self.window makeKeyAndOrderFront:self]; // Display window.
}

@end

Can can make call -makeCurrentContext in your -prepareOpenGl method. All that I have written below is not necessary but nice for performance reasons. I have started using the CVDisplayLink to sync frame drawing with the screen refresh rate so my openGLview looks like

// This is the callback function for the display link.
static CVReturn OpenGLViewCoreProfileCallBack(CVDisplayLinkRef displayLink,
                                              const CVTimeStamp* now, 
                                              const CVTimeStamp* outputTime, 
                                              CVOptionFlags flagsIn, 
                          CVOptionFlags *flagsOut, 
                                              void *displayLinkContext) {
    @autoreleasepool {
        OpenGLViewCoreProfile *view = (__bridge OpenGLViewCoreProfile*)displayLinkContext;
        [view.openGLContext makeCurrentContext];
        CGLLockContext(view.openGLContext.CGLContextObj); // This is needed because this isn't running on the main thread.
        [view drawRect:view.bounds]; // Draw the scene. This doesn't need to be in the drawRect method.
        CGLUnlockContext(view.openGLContext.CGLContextObj);
        CGLFlushDrawable(view.openGLContext.CGLContextObj); // This does glFlush() for you.

        return kCVReturnSuccess;
    }
}

- (void)reshape {
    [super reshape];
    CGLLockContext(self.openGLContext.CGLContextObj);

    ... // standard opengl reshape stuff goes here.

    CGLUnlockContext(self.openGLContext.CGLContextObj);
}

- (void)prepareOpenGL {
    [super prepareOpenGL];

    [self.openGLContext makeCurrentContext];
    GLint swapInt = 1;
    [self.openGLContext setValues:&swapInt forParameter:NSOpenGLCPSwapInterval];

    CGLLockContext(self.openGLContext.CGLContextObj);

    ... // all opengl prep goes here

    CGLUnlockContext(self.openGLContext.CGLContextObj);

    // Below creates the display link and tell it what function to call when it needs to draw a frame.
    CVDisplayLinkCreateWithActiveCGDisplays(&_displayLink);
    CVDisplayLinkSetOutputCallback(self.displayLink, &OpenGLViewCoreProfileCallBack, (__bridge void *)self);
    CVDisplayLinkSetCurrentCGDisplayFromOpenGLContext(self.displayLink, 
                                                      self.openGLContext.CGLContextObj, 
                                                      self.pixelFormat.CGLPixelFormatObj);
    CVDisplayLinkStart(self.displayLink);
}