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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