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Difference of Rectangles

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Jerome Peace

Difference of Rectangles

Difference of Rectangles

Hi JIm,

The following is some workspace code (copy into a
workspace.
Select and do all of it. Then recolor and move the
rectangles around.
And select and do the last bit.

note: #flipRotated: is new as of 3.9. I don't know
how people got along without it.

aLessB :=
[ :a :b | | overlap |
overlap := a intersect: b .
overlap area = 0
ifTrue: [ a corners ]
ifFalse: [ overlap area < a area
ifFalse: [ a corners ]
ifTrue: [oCorners := overlap corners .
verts := OrderedCollection new .
a corners withIndexDo: [ :each :eachIndex |
((oCorners at: eachIndex) dist: each) < 1
ifTrue: [ verts
addAll: ( oCorners
flipRotated: eachIndex negated * 2
+ 1)
allButLast ]
ifFalse: [ verts add: each ] ] . verts ] ] ].

aRect := RectangleMorph new openCenteredInWorld .
bRect := RectangleMorph new openCenteredInWorld .
poly := PolygonMorph new openCenteredInWorld .

polyVerts :=
aLessB value: aRect bounds
value: bRect bounds .
poly setVertices: polyVerts; changed .

I had done something similar for puzzle pieces. And I
had fun working this one out.

Yours in curiosity and service, --Jerome Peace

> Jim Rosenberg jr at amanue.com
> Sun May 6 20:12:03 UTC 2007

>
> Consider two rectangles, a and b. The only
constraint I
> will put on them is
> that neither contains the other. I wish to create a
> PolygonMorph
> programmatically consisting of a merge: b with b
> removed but all of a
> retained in the case a and b overlap. I think I see
my

> way to how to do
> this, but if anyone knows of any code I can look at
> where something like
> this is already implemented I'd be much obliged.
>
> My idea for how to go about this is to use "turtle
> logic" more or less as
> follows: Start with the first vertex of a merge: b
> which is not inside of
> b. Proceed clockwise along the bounds of a merge:

b; if
> you hit b turn
> left, if you hit a turn right. But this may be
doing
> things the hard way.
>
> -Thanks, Jim

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Jerome Peace

Re: Difference of Rectangles

Hi Dan.

Yep

I hadn't thought of that case. Also missed the case
where the two rectanges share a width or a height and
overlap like playing cards on a solitare layout.

Back to the drawing board. Worthy problems prove their
worth by fighting back. :-)

Yours in curiosity and service, --Jerome Peace

--- Dan Ingalls <[hidden email]> wrote:

> Hi, Jerome -
>
> Your code is interesting, but it did not seem to
> work for me in the
> case of, eg...
>
> AAAA
> ABBA
> BB
>
> But I haven't got anything better, either ;-).
>
> - Dan
> ------------------------------------
> >Difference of Rectangles
> >
> >Hi JIm,
> >
> >The following is some workspace code (copy into a
> >workspace.
> >Select and do all of it. Then recolor and move the
> >rectangles around.
> >And select and do the last bit.
> >
> >note: #flipRotated: is new as of 3.9. I don't know
> >how people got along without it.
> >
> >aLessB :=
> >[ :a :b | | overlap |
> > overlap := a intersect: b .
> > overlap area = 0
> > ifTrue: [ a corners ]
> > ifFalse: [ overlap area < a area
> > ifFalse: [ a corners ]
> > ifTrue: [oCorners := overlap corners .
> > verts :=
> >OrderedCollection new .
> > a corners
> >withIndexDo: [ :each :eachIndex |
> >
> > ((oCorners at: eachIndex) dist: each) < 1
> >
> > ifTrue: [ verts
> >
> > addAll: ( oCorners
> >
> > flipRotated:
> >eachIndex negated * 2
> >
> > + 1)
> >
> > allButLast ]
> >
> > ifFalse: [ verts add: each ] ] . verts ] ] ].
> >
> >
> >
> >aRect := RectangleMorph new openCenteredInWorld .
> >bRect := RectangleMorph new openCenteredInWorld .
> >poly := PolygonMorph new openCenteredInWorld .
> >
> >polyVerts :=
> >aLessB value: aRect bounds
> > value: bRect bounds .
> >poly setVertices: polyVerts; changed .
> >
> >I had done something similar for puzzle pieces. And
> I
> >had fun working this one out.
> >
> >Yours in curiosity and service, --Jerome Peace
> >
> >
> >
> >
> >> Jim Rosenberg jr at amanue.com
> >> Sun May 6 20:12:03 UTC 2007
> >
> >>
> >> Consider two rectangles, a and b. The only
> >constraint I
> >> will put on them is
> >> that neither contains the other. I wish to
> create a
> >> PolygonMorph
> >> programmatically consisting of a merge: b with
> b
> >> removed but all of a
> >> retained in the case a and b overlap. I think I
> see
> >my
> >> way to how to do
> >> this, but if anyone knows of any code I can
> look at
> >> where something like
> >> this is already implemented I'd be much
> obliged.
> >>
> >> My idea for how to go about this is to use
> "turtle
> >> logic" more or less as
> >> follows: Start with the first vertex of a
> merge: b
> >> which is not inside of
> >> b. Proceed clockwise along the bounds of a
> merge:
> >b; if
> >> you hit b turn
> >> left, if you hit a turn right. But this may be
> >doing
> >> things the hard way.
> >>
> >> -Thanks, Jim
> >
> >
> >
> >
>
>____________________________________________________________________________________
> >The fish are biting.
> >Get more visitors on your site using Yahoo! Search
> Marketing.
>
>http://searchmarketing.yahoo.com/arp/sponsoredsearch_v2.php
>

____________________________________________________________________________________
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