Minimal cocoa text entry for OpenGL apps

minimal_cocoa_gl_text_entry.m

// *DISCLAIMER IF YOU FOUND THIS VIA GOOGLE: I'm at the time of writing still figuring this out, it
// works for me but I don't actually know if it's correct yet*
//
// This is a minimal example of how one might accept text entry in Cocoa in an OpenGL app or
// such. Unlike using `[event characters]`, it ignores unprintable keys such as the arrow keys. It
// also allows you to type accents and such, e.g. `alt+e o`. This example contains no error
// checking, and the only way to exit it is to kill it from the command line.
//
// To execute it, run:
// `$ gcc minimal_cocoa_gl_text_entry.m -framework Cocoa && ./a.out`

#import <Cocoa/Cocoa.h>

// We need to create a new subclass of `NsView` that implements the `NSTextInputClient` protocol.
// NSView can be replaced with NSOpenGLView or such here if needed.
//
// It's possible that instead you could just have a separate `NSTextInputClient` object, and send
// the `keyDown` events to it from here instead. I haven't yet tried this.
@interface MyView : NSView<NSTextInputClient>
{
}
@end

@implementation MyView
    // Accept first responder so we get events
    - (BOOL)acceptsFirstResponder {
        return YES;
    }

    // Interpret the key events as text
    - (void)keyDown:(NSEvent *)event {
        [self interpretKeyEvents:[NSArray arrayWithObject:event]];
    }

    // Just log the text as we get it to show that it works
    - (void)insertText:(id)string replacementRange:(NSRange)replacementRange {
        NSLog(@"%@", string);
    }

    // The rest of these are methods I don't yet understand and have just filled in stubs for so it
    // would compile.
    - (BOOL)hasMarkedText {
        return NO;
    }

    - (NSRange)markedRange {
        return NSMakeRange(0, 0);
    }

    - (NSRange)selectedRange {
        return NSMakeRange(0, 0);
    }

    - (void)setMarkedText:(id)string
            selectedRange:(NSRange)selectedRange
         replacementRange:(NSRange)replacementRange {
     }

    - (void)unmarkText {
    }

    - (NSArray*)validAttributesForMarkedText {
        return [NSArray array];
    }

    - (NSAttributedString*)attributedSubstringForProposedRange:(NSRange)range
                                                   actualRange:(NSRangePointer)actualRange {
        return nil;
    }

    - (NSUInteger)characterIndexForPoint:(NSPoint)point {
        return 0;
    }

    - (NSRect)firstRectForCharacterRange:(NSRange)range
                             actualRange:(NSRangePointer)actualRange {
        return NSMakeRect(0, 0, 0, 0);
    }

    - (void)doCommandBySelector:(SEL)selector {
    }
@end

int main() {
    @autoreleasepool {
        NSApplication* app = [NSApplication sharedApplication];
        [app setActivationPolicy: NSApplicationActivationPolicyRegular];

        NSWindow *window = [[[NSWindow alloc]
            initWithContentRect: NSMakeRect(0, 0, 200, 200)
            styleMask: NSWindowStyleMaskTitled
            backing: NSBackingStoreBuffered
            defer: NO
        ] autorelease];

        [window setContentView: [[MyView alloc] init]]; // Here we're using our custom view

        [window cascadeTopLeftFromPoint:NSMakePoint(20,20)];
        [window makeKeyAndOrderFront:nil];
        [NSApp activateIgnoringOtherApps:YES];
        [app run];
    }
    return 0;
}