Clipping a path to a boundary

* Clipping a path to a boundary
@ 2005-08-07 19:16 David Arnold
  2005-08-07 21:56 ` Hans Hagen
  0 siblings, 1 reply; 4+ messages in thread
From: David Arnold @ 2005-08-07 19:16 UTC (permalink / raw)

All,

I'm looking for a new idea for something I need to do. I typically 
create a path on a domain [-5,5] as follows, a arbitrary. Then I 
randomly reflect the path about and axis, a line, or maybe rotate it. 
The result is that parts of the path may lie outside a bounding window.

% define linear function f
vardef f(expr x)=
	a*x*x
enddef;

% define paths for functions f, g, and h, respectively
path P;

P:=(-5,f(-5));
for x=-5 step .1 until 5:
	P:=P--(x,f(x));
endfor;

% initialize scale
numeric u; 10u=w;

% scale and draw graph
P:=P scaled u;
draw P withcolor blue;

% clipping path
path cpath;
cpath:=(-5,-5)--(5,-5)--(5,5)--(-5,5)--cycle;
cpath:=cpath scaled 1u;

% clip and save current picture
picture pic;
clip currentpicture to cpath;
pic:=currentpicture;

% erase currentpicture
currentpicture:=nullpicture;

Then I do some stuff I need to do and bring back the path at a later 
time with:

draw pic;

This works fine. However, what I need to do is somehow clip the path P 
to the bounding box, but retain the resulting cutpath in a path 
variable Q. That is, I need to cut off the parts of the path P that lie 
outside the bounding box cpath:=(-5,-5)--(5,-5)--(5,5)--(-5,5)--cycle 
and store the clipped path in the path variable Q. The difficulty is I 
have no advance knowledge if the path P lies entirely inside the 
bounding box or if it escapes through one of the sides.

Any hints, tips, etc., would be very appreciated.

Thanks.

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