GP: ALGORITHM : Flipping a point across a line

["justin howard" <lordjuz@Hotmail.com>]

>Hello peeps,
>
>Would anyone happen to know how to calculate the reflected coordinates of
>a point, on one side of a line, to the other.


An algorithm could be something like this...
(this is running from my head as im typing so dont expect this tio be 
perfect but)
...
point1=(x1,y1)
line has equation y=mx+c

for point2(x2,y2)
----------
hyp=sin(tan-1(m))*(sqrt((mx1+c-y1)^2))
c=2*hyp
deltay=(hyp) * (cos(90-(tan-1(m))))
deltax=(hyp) * (sin(90-(tan-1(m))))
therefore...
x2=x1+deltax
y2=y1+deltay


to explain what hyp and deltax and deltay and c are I need to draw diagrams
all it generally does is...
# calculate the direct distance from the point to the line
# double it to get distance from point1 to point 2
# calculate rise and run of that distance
  which is deltax and deltay
  which is the distance in x units from point 1 to point 2
and distance in y units from y1 to y2
# hence new points coordinates are just the original ones +- the chanegs in 
x and y needed to get to next point

hope that was useful in some way

______________________________________________________
Get Your Private, Free Email at http://www.hotmail.com
=================================================================
To SUBSCRIBE or UNSUBSCRIBE please visit
http://gameprogrammer.com/mailinglist.html