Question

I am trying to programmatically create a Cocoa window with an OpenGL context for an OS X application. I have been unable to find an example online which does not use the Interface Builder for creating a window and OpenGL view.

All I want is for glClear to make my window magenta (0xFF00FF). However, the window remains white.

Here is my project:

AppDelegate.h

#import <Cocoa/Cocoa.h>

@interface AppDelegate : NSObject <NSApplicationDelegate> {
    NSWindow *window;
    NSOpenGLContext *openGLContext;
}

@property (assign) NSWindow *window;
@property (assign) NSOpenGLContext *openGLContext;

- (void)draw;

@end

AppDelegate.m

#import "AppDelegate.h"

@implementation AppDelegate

@synthesize window;
@synthesize openGLContext;

static NSOpenGLPixelFormatAttribute glAttributes[] = {
    0
};

- (void)draw {
    NSLog(@"Drawing...");

    [self.openGLContext makeCurrentContext];

    glClearColor(1, 0, 1, 1);
    glClear(GL_COLOR_BUFFER_BIT);

    [self.openGLContext flushBuffer];
}

- (void)applicationDidFinishLaunching:(NSNotification *)aNotification {
    NSRect frame = NSMakeRect(0, 0, 200, 200);

    self.window = [[[NSWindow alloc]
        initWithContentRect:frame
        styleMask:NSBorderlessWindowMask
        backing:NSBackingStoreBuffered
        defer:NO] autorelease];
    [self.window makeKeyAndOrderFront:nil];

    NSOpenGLPixelFormat *pixelFormat
        = [[NSOpenGLPixelFormat alloc] initWithAttributes:glAttributes];
    self.openGLContext = [[NSOpenGLContext alloc]
        initWithFormat:pixelFormat shareContext:nil];
    [self.openGLContext setView:[self.window contentView]];

    [NSTimer
        scheduledTimerWithTimeInterval:.1
        target:self
        selector:@selector(draw)
        userInfo:nil
        repeats:YES];
}

- (BOOL)applicationShouldTerminateAfterLastWindowClosed:(NSApplication *)_app {
    return YES;
}

@end

main.m

#import "AppDelegate.h"

#import <Cocoa/Cocoa.h>

int main(int argc, char **argv) {
    AppDelegate *appDelegate = [[AppDelegate alloc] init];
    return NSApplicationMain(argc, (const char **) argv);
}

Answer 1

The documentation for -[NSOpenGLContext flushBuffer] says:

Discussion

If the receiver is not a double-buffered context, this call does nothing.

You can cause your context to be double-buffered by including NSOpenGLPFADoubleBuffer in your pixel format attributes. Alternatively, you can call glFlush() instead of -[NSOpenGLContext flushBuffer] and leave your context single-buffered.