I was trying to make a bouncing circle program,I hope if the circle reach the edge of the form, it will bounce back, I used the following coding:
if X+100 >= me.with then,
x = me.with -100
if y+100 >= me.height then
y = me.height-100

However, it seems the circle is still drawn have in form, half off the form,

Could anybody tell me why please?

Thanks

The alogorithim for this isn't that simplistic. I have done something similar using the XNA framework but can't remember the exact alogoritihim.

http://msikes.spaces.live.com/Blog/

that link is an XNA resource, ignore all of the Draw and Update code and focus on the calculations that are preformed about half way down through the source.

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What is the diameter of the circle? If it's greater than 100, then it would stick off the edge of the form sometimes.

Usually I just reverse the direction of movement and don't worry if the ball moves a little off the screen. See this example:

    http://www.vb-helper.com/howto_net_bouncing_ball.html

Rod

Rod
[email protected]
Author of "Visual Basic 2005 Programmer's Reference"
http://www.vb-helper.com/vb_prog_ref.htm

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It works! Thanks for all your help. After reading Mr Stephen's bouncing ball example, I used Me.ClientSize.Width and Me.ClientSize.height for checking the boundary, it works perfect.
 I used me.width and me.height before, it returns a slightly bigger value than client size, and therefore the ball always slips half outside the screen.

Thanks again