Hello World!
I'm talking about calculating distance in Alice3.
I have a movie with an ice skater and an ice floe.
What I would like to do
is have the skater move next to the ice floe.
My initial attempt
would be to say,
I want the ice skater to move to the ice floe.
When we run that,  you can see,
she's right smack in the middle of the ice floe.
the problem is
when we calculate something,
The distance is from the center pivot point
of each of the objects.
So  the skater move from here
to the pivot point, or middle of the ice floe.
That's not going to work I'm going to
disable that.  When I'm experimenting,
if I disable something I can look back
so I don't repeat something that didn't work previously.
When I get all finished, I can delete these.
We're going to need to move the skater
from here, to here,
minus the width of the ice floe.
So we need a little bit of math, and we need some variables.
My first variable is going to be a double
and call this distanceToMove.
We're going to give it initial value, it doesn't matter what.
And say OK.
I'm going to go to functions
Procedures are things that happen.
Functions give answers.
So I'm going to use
Ice skater.getDistanceTo
some other object,  and drag that
and replace that .25
and I want the distance
to the ice floe.
So the distance to move
is the ice skaters distance to the ice floe.
That's not  quite it yet,
but let's just try that
going back to the procedures,
and have the ice skater  move forward
distanceToMove
If we run that,
she's still going to the middle of the ice floe,
but I'm going to
keep working on the math,
I'm  going to have another variable, also a double called
halfWidthIce.
Again,  giving that any value,
because we're going to replace it.
So the halfWidthIce
I need to now go to the icefloe.
I go to the functions
and select getWidth,
and drag that to replace that.
(I'm going to make this screen a little smaller
on this side, so that we can see more of the code.)
Instead of just the width,
I want half of the width.
so I'm going to select math
and it's going to be
the icefloe.width / 2
And you can see what  I selected now,
I know that was off the screen a little bit.
So I have the distanceToMove
The whole thing would put her in the middle of the ice floe.
Then I have half the width of the ice floe,
and I want to subtract this
from that total distance.
To do, I'm going to use an assignment statement
and distanceToMove is
equal to distanceToMove,
another math problem:  distance to move minus
half the width of the ice.
Let's run it.
and she stops
right at the edge of the ice floe.
It's possible
that we also have to subtract
half the width of the person
to have them move exactly where wanted.
You should experiment with that
Until  you are comfortable with
creating these math equations.