is within ... polygon shape?

[Lynch, Jonathan]

How about this technique...

This would work as long as the two objects are not the exact same color.


Step one:
Put object 1 on top of object 2
Take a snapshot of the rect that contains both objects
Put the imagedata for that snapshot into tImageData1

Step two:
Put object 2 on top of object 1
Take a snapshot of the rect that contains both objects
Put the imagedata for that snapshot into tImageData2

If tImageData1 <> tImageData2 then return true


Basically, the idea is that, as long as the visible portions do not
overlap, the image of the rect that contains both objects will be the
same, regardless of which is on top. If the image of that rect changes
when the Z order changes, then they must overlap.



-----Original Message-----
From: use-revolution-bounces at lists.runrev.com
[mailto:use-revolution-bounces at lists.runrev.com] On Behalf Of Lynch,
Jonathan
Sent: Friday, June 24, 2005 11:54 AM
To: How to use Revolution
Subject: RE: is within ... polygon shape?

This is pretty cool!

But - would this work 100% for curved polygons or images?

The docs do not mention points for images.

Either, this is a very cool way of testing.

-----Original Message-----
From: use-revolution-bounces at lists.runrev.com
[mailto:use-revolution-bounces at lists.runrev.com] On Behalf Of Jim Hurley
Sent: Friday, June 24, 2005 11:44 AM
To: use-revolution at lists.runrev.com
Subject: Re: is within ... polygon shape?

>
>Message: 15
>Date: Fri, 24 Jun 2005 07:53:22 -0700
>From: Scott Rossi <scott at tactilemedia.com>
>Subject: Re: is within ... polygon shape?
>To: How to use Revolution <use-revolution at lists.runrev.com>
>Message-ID: <BEE16C72.1AE70%scott at tactilemedia.com>
>Content-Type: text/plain; charset="US-ASCII"
>
>Recently, Steve Bonham  wrote:
>
>>  Intersect doesn't work after all. It appears that one object will
>>  intersect with another irregular object's rect and NOT the objects
>  > true shape (polygon points).
>>  See illustration... at:
>>  http://academics.georgiasouthern.edu/cet/SB/ball_fairway.jpg
>>
>>  Is there a way to get Rev to:
>>  1. evaluate IF the loc of an object is within the shape (defined by
a
>>  series of coordinates) of an object?
>>
>>  OR
>>  2. evaluate IF the loc of an object intersects with the shape
>>  (defined by a series of coordinates) of an object?
>
>I believe some folks on the list have written collision detection
routines
>that can detect intersection in several situations.  I think Malte
Brill
>might know something about this.
>
>That being said, collision detection on irregular shapes can work by
using
>images that have a transparent background and point references.  Using
the
>within() function it is possible to accurately detect whether a point
falls
>within the image since Rev will evaluate a point falling within the
>transparent region of the image as false.
>
>  get within(img 1,myPoint)
>
>Regards,
>
>Scott Rossi
>Creative Director
>Tactile Media, Multimedia & Design

Steve,

Scott is right. The function you  want is "within()", which is 
different from "is within." It is very efficient.

If you want to detect whether two polygons Poly1 and Poly2 intersect, 
you would first run

function firstWithinSecond grc1,grc2
   put the points of grc grc1 into myPolyPoints1
   repeat for each line tPoint in myPolyPoints1
     if   within(grc grc2,tPoint)  then return "true"
   end repeat
   return false
end firstWithinSecond

where grc1 is Poly1 and grc2 is Poly2 and then run the same routine 
with Poly1 and Poly2 reversed.

It may be that a point (vertex) of Poly2 is within Poly1, but there 
is no vertex of Poly 1 which is within Poly2. You need to run both. 
Or write one handler to check both.

I didn't realize it worked for points within images as well. Thanks
Scott.

Jim




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