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From: bernard@cs.colorado.edu (Bernie Bernstein)
Newsgroups: comp.sys.mac.programmer
Subject: Re: Arrowheads anyone?
Message-ID: <1991Mar5.190538.778@csn.org>
Date: 5 Mar 91 19:05:38 GMT
References: <2867@krafla.rhi.hi.is>
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Organization: University of Colorado, Boulder
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In article <2867@krafla.rhi.hi.is>, ebth@rhi.hi.is (Eggert Bjarni Thorlacius) writes:
> 
> Hello everybody.
> 
> OK, here is the situation.  I've got two points on screen, and I want to draw
> an arrow between them.  Does anyone hvae any code that does something remotely
> like this?
>

/***
 * ArrowPoints
 *
 *	This function sets two points which can be used to construct
 *  an arrowhead.  The arrow will be on the end of the line.  To
 *  draw a line made with this function, one would:
 *  	MoveTo(start.h, start.v);
 * 		LineTo(end.h, end.v);
 *  	LineTo(new1.h, new1.v);
 *  	MoveTo(end.h, end.v);
 *  	LineTo(new2.h, new2.v);
 *	or you can create a polygon connecting the end point and the two new
 *  points and fill or frame it.  In any case, it works well enough for
 *  my application.  I wouldn't do this at update time.  Do it once when
 *  the line points change and save the arrow points.
 *
 *		Point start;		starting point for the line
 *		Point end;			ending point for the line
 *		Point *new1;		endpoint of half of arrowhead
 *		Point *new2;		endpoint of other half of arrowhead
 ***/
void ArrowPoints(Point start, Point end, Point *new1, Point *new2)
{
	double	theta, theta1, theta2;
	short	tx, ty;
	double	pitch = .3;			/* angle of the arrow lines from the mail line */
	short	length = 8;			/* length of the arrow lines */
	
	tx = end.h;
	ty = end.v;
	
	theta = atan2((start.v - ty), (start.h - tx));
	theta1 = theta + pitch;
	theta2 = theta - pitch;
	
	new1->h = (short)(tx + (length * cos(theta1)));
	new1->v = (short)(ty + (length * sin(theta1)));
	new2->h = (short)(tx + (length * cos(theta2)));
	new2->v = (short)(ty + (length * sin(theta2)));
}


I wrote this in Think C a long time ago.  I would be interested in hearing
from others who have faster ways to do this.

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