Detect when an object touches the edge of the screen

Question

If I have an object of arbitrary height and width that moves around the screen, what's an elegant way of detecting when it touches the edge of the screen?

Answer 1

This depends on your coordinate system. Assuming a coordinate system with (0|0) at the lower left corner you have those cases:

• Touches left edge if object.origin.x <= 0
• Touches right edge if object.origin.x + object.size.width >= screenSize.width
• Touches bottom edge if object.origin.y <= 0
• Touches top edge if object.origin.y + object.size.height >= screenSize.height

This also works for irregular shaped objects if you use the bounding rectangle for the object.