a.m

- (void)drawRect:(NSRect)dirtyRect
{
    NSGraphicsContext *graphicContext = [NSGraphicsContext currentContext];
    CGContextRef context = [graphicContext graphicsPort];
    
    // Set the origin of the coordinate system in the upper left corner instead of the lower left corner.
    CGContextConcatCTM(context,
                       CGAffineTransformMake(1.0, 0.0, 0.0, -1.0, 0.0, self.frame.size.height));
}

b.m

- (BOOL)isFlipped
{
    return YES;
}