Borders

General
1

Hi,

How can I set borders so that they will make objects stop moving when they hit the border?

2

You have whatever code you’re using that moves the object check to see if it’s at the border, then not move it.


function setup()
   dx=1
   x=50
end

function draw()
   x = x + dx
   if ((x >= 100) or (x <= 10)) then dx=0 - dx end
   sprite(yoursprite, x, 100)
end

“dx = 0 - dx” is an easy way to toggle between -1 and 1 (or -5 and 5 or whatever), ie. “reverse direction”. The code above would bounce your sprite back and forth betwen 10 and 100. reacting to other barriers in other places is just extending that - maybe you have a table of “bumpers” and you check to see if you hit any of them, then react accordingly.

3

Well if you know where your objects are you can see where they are in relation to the screen’s width and height (obtainable via the WIDTH and HEIGHT constants).

Have a look at Mark’s recent response to a similar question here:
http://twolivesleft.com/Codea/Talk/discussion/comment/2954#Comment_2954

Edit: Or Mr. Bortels’ above.

4

0 - dx???

Isn’t that just the same as -dx? Or does lua have some funny definition of 0 that no-one’s told us mathematicians about?

5

I hate the unary minus, it killed my father? Dunno. it just came out of my brain that way.

I suspect it’s inlined as constant expression and turned into “-dx” anyway. It would be in any decent C compiler, for sure.

Difference between a Mathematician and an Engineer:

Mathematician: The zero is unnecessary.

Engineer: Sweet, it works.

6

ah, yeah. i implemented borders in a way that is 100000 times more complicated.

Sweet, it works.