Drawing a bridge with Quartz 2D

Question

I'm trying to draw the following image:

Using this objective-c code:

CGContextSetFillColorWithColor(ctx, [[UIColor redColor] CGColor]);
CGContextMoveToPoint(ctx, position.X - (size.width / 2), position.Y - (size.height / 2));
CGContextAddLineToPoint(ctx, position.X - (size.width / 2), position.Y + (size.height / 2));
CGContextAddLineToPoint(ctx, position.X - (size.width / 4), position.Y + (size.height / 2));
CGContextAddArc(ctx, position.X, position.Y + (size.height / 2), (size.width / 4), -M_PI, M_PI, 0);
CGContextAddLineToPoint(ctx, position.X + (size.width / 2), position.Y + (size.height / 2));
CGContextAddLineToPoint(ctx, position.X + (size.width / 2), position.Y - (size.height / 2));
CGContextFillPath(ctx);

But it doesn't work. I get this image:

The width of the image is size.width and the height is size.height. The origin is (position.X, position.Y). This point is in center, at (size.width /2, size.height / 2).

The first point is the upper left corner, and the second one is the bottom left corner. And then continues to the right.

Here is a better explanation:

Sorry for my English.

Any advice?