Bouncing?

> Hi all,
>
> I've been doing some searching on this topic and haven't been able  
> to find answers to my questions. So....
>
> I'm trying to use the bounce command in games (like Pong). Can  
> anyone explain to me -
>
> 1. Does bounce require a playfield to bounce off? I've tried  
> testing to see if a ball's color see the color of a wall, and then  
> bouncing if it does. But that doesn't seem to work. I know the  
> ball's color can see the wall's color, because I've also had it  
> croak if it sees the wall. The ball croaks and keeps on going  
> through the wall.
>
> 2. Exactly how is the bounce calculated? When I put the ball in a  
> playfield, then make a colored box the same size as the playfield,  
> it will bounce and most of the time the bounce is "true". Every so  
> often the bounce is the opposite of what you expect. Does anyone  
> know why this is? Would I be better off to use a variable for the  
> heading and calculate it, thus inducing the correct "bounce"?
>
> I hope these questions are clear.
>
> Thanks in advance,
>
> Bob Irving
> Middle School Technology Facilitator
> Lancaster Country Day School
> Lancaster, PA
> Blog: http://cougar.e-lcds.org/wordpress/
> "In times of change, learners inherit the earth, while the Learned  
> find
> themselves equipped to deal with a world that no longer exists."
> Eric Hoffer
> _______________________________________________
> Squeakland mailing list
> [hidden email]
> http://squeakland.org/mailman/listinfo/squeakland

>Hi, Bob,
>
>Short answer:  The "bounce" of etoys doesn't do what you, or any
>reasonable person, might expect it to.  So yes, you are best off
>computing coordinates directly in your own scripts, rather than
>trying to use "bounce".
>
>Within its limited range of ability, "bounce" can be useful for
>keeping moving objects onscreen without too much effort.
>
>Beyond that, however, "bounce" is a pretty strange beast, best avoided.
>
>However, for anyone still interested, read on...
>
>-------------
>
>When I tell a ball "Ball forward by 10" I expect to see it move
>forward, and it does.  When I tell a ball "Ball bounce croak", I
>might well expect to see and hear something happen, some sort of
>reversal of direction, some sort of froggy sound, but instead it
>doesn't seem to do anything.  Why is that?
>
>It's because Squeak's "bounce" has a very narrow and less-than-
>obvious meaning, something along the lines of:  "If I've just crossed
>the edge of my container, then change my direction and position to
>make me appear to have just bounced off the edge and returned to the
>interior."
>
>Unless scripts affecting the position of your object have just made
>it cross the edge of its container (from a position previously wholly
>within the container,) telling it to "bounce" will appear to have no
>effect.   Unlike any other etoy command, it has its own implicit,
>built-in "conditional" or "Test" having to do with the motion brought
>about by currently-running scripts, relative to where the edges of
>the container are.  This bit of magic can be used to nice effect in
>some demos, but in practice it's pretty strange if you try to harness
>it for anything interesting.
>
>To meet the beast head-on, paint a Frog, rotate it slightly, drop it
>into a Playfield, then build the script:
>
>         Frog forward by 5
>         Frog bounce croak
>
>When you set this script to ticking, the Frog repeatedly goes forward
>by 5 units, but it does not repeatedly "bounce", by any reasonable
>interpretation of the word "bounce", nor does it croak -- in fact the
>bounce request doesn't seem to do anything at all.
>
>Until... the Frog approaches the boundary of its container.  When it
>reaches or crosses such an edge, because of the "bounce" command, it
>magically gets its heading, its x, and its y adjusted to give the
>appearance of "bouncing off the edge of the container".  And only
>then is the croak heard.
>
>This is all that "bounce" can do.  You don't get to choose what the
>object is to bounce off *of* (if the bounce does happen, it will
>always bounce off of whatever edge of its container it has just
>crossed,) nor by how *much* it should bounce (that is computed based
>on its imputed speed, which is based on where it was before and where
>it would be without the bounce afterward) -- nor even *when* the
>bounce will take place (that is based on the "just-reached-edge-of-
>container" test implicitly built into the "bounce" command.)
>
>So to summarize... because of the above limitations, and because or
>the maddening fact that when you tell an object to bounce it usually
>does nothing, I do not  recommend using "bounce" for anything except
>for those familiar, simple "forward by/bounce" scripts.
>
>
>It would be interesting to hear some suggestions and discussion on
>this list regarding possible improvements to the set of commands in
>the standard etoy vocabulary.
>
>
>Cheers,
>
>    -- Scott
>
>
>
>On Jan 5, 2007, at 4:00 PM, Bob Irving wrote:
>
> > Hi all,
> >
> > I've been doing some searching on this topic and haven't been able
> > to find answers to my questions. So....
> >
> > I'm trying to use the bounce command in games (like Pong). Can
> > anyone explain to me -
> >
> > 1. Does bounce require a playfield to bounce off? I've tried
> > testing to see if a ball's color see the color of a wall, and then
> > bouncing if it does. But that doesn't seem to work. I know the
> > ball's color can see the wall's color, because I've also had it
> > croak if it sees the wall. The ball croaks and keeps on going
> > through the wall.
> >
> > 2. Exactly how is the bounce calculated? When I put the ball in a
> > playfield, then make a colored box the same size as the playfield,
> > it will bounce and most of the time the bounce is "true". Every so
> > often the bounce is the opposite of what you expect. Does anyone
> > know why this is? Would I be better off to use a variable for the
> > heading and calculate it, thus inducing the correct "bounce"?
> >
> > I hope these questions are clear.
> >
> > Thanks in advance,
> >
> > Bob Irving
> > Middle School Technology Facilitator
> > Lancaster Country Day School
> > Lancaster, PA
> > Blog: http://cougar.e-lcds.org/wordpress/
> > "In times of change, learners inherit the earth, while the Learned
> > find
> > themselves equipped to deal with a world that no longer exists."
> > Eric Hoffer
> > _______________________________________________
> > Squeakland mailing list
> > [hidden email]
> > http://squeakland.org/mailman/listinfo/squeakland
>
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