Question

I have my app on iPhone with a UIViewController with some stuff inside.. image, textbox, etc…
is there a way to draw a line or something like this using opengl directly inside the UIViewController?

thanks in advance

Answer 1

Are you sure about the OpenGL?

I believe it will be impossible to use OpenGL above regular views.

You might add a custom view (inherit from UIView) above all the other views and draw anything you want on that view.
This view should have a transparent background color.
In addition, if you want to interact with the other views (tap buttons, edit text views, scroll etc.) then you will have to implement the hitTest method in your custom view in order to pass the touch event to the views that are located under this one…

EDIT: Don’t mess with the hitTest. Just uncheck the User Interaction Enabled in the XIB…

EDIT: Code sample:

@interface TransparentDrawingView : UIView {
    CGPoint fromPoint;
    CGPoint toPoint;
}
- (void)drawLineFrom:(CGPoint)from to:(CGPoint)to;
@end

@implementation TransparentDrawingView

- (void)initObject {
    // Initialization code
    [super setBackgroundColor:[UIColor clearColor]];
}
- (id)initWithFrame:(CGRect)frame {
    if (self = [super initWithFrame:frame]) {
        // Initialization code
        [self initObject];
    }
    return self;
}
- (id)initWithCoder:(NSCoder *)aCoder {
    if (self = [super initWithCoder:aCoder]) {
        // Initialization code
        [self initObject];
    }
    return self;
}

- (void)drawRect:(CGRect)rect {
    // Drawing code

    // Draw a line from 'fromPoint' to 'toPoint'
}
- (void)drawLineFrom:(CGPoint)from to:(CGPoint)to {
    fromPoint = from;
    toPoint = to;

    // Refresh
    [self setNeedsDisplay];
}

@end