(I forgot my pw, so have to post a new)
Thank you so much for your reply, Chennes and Peverbian!
Peverbian, I tried your suggestion, Yes it works!!
And also I find my problem comes from the abs function
if I change it to
if(x>1.5 | | x<-1.5 | | y>1.5 | | y<-1.5)…
if(abs(x)>1.5 | | abs(y)>1.5)
It also works, the ball won’t go beyond the rectangle border.
I think abs return a integer instead of a float–which I thought it should be.
Anyway thank you so much