[micropolis] / src / tk / tktrig.c

/* 
 * tkTrig.c --
 *
 *	This file contains a collection of trigonometry utility
 *	routines that are used by Tk and in particular by the
 *	canvas code.  It also has miscellaneous geometry functions
 *	used by canvases.
 *
 * Copyright 1992 Regents of the University of California.
 * Permission to use, copy, modify, and distribute this
 * software and its documentation for any purpose and without
 * fee is hereby granted, provided that the above copyright
 * notice appear in all copies.  The University of California
 * makes no representations about the suitability of this
 * software for any purpose.  It is provided "as is" without
 * express or implied warranty.
 */

#ifndef lint
static char rcsid[] = "$Header: /user6/ouster/wish/RCS/tkTrig.c,v 1.8 92/08/24 09:24:14 ouster Exp $ SPRITE (Berkeley)";
#endif

#include <stdio.h>
#include <math.h>
#include "tkconfig.h"
#include "tkcanvas.h"

#undef MIN
#define MIN(a,b) (((a) < (b)) ? (a) : (b))
#undef MAX
#define MAX(a,b) (((a) > (b)) ? (a) : (b))
#define PI 3.14159265358979323846
\f
/*
 *--------------------------------------------------------------
 *
 * TkLineToPoint --
 *
 *	Compute the distance from a point to a finite line segment.
 *
 * Results:
 *	The return value is the distance from the line segment
 *	whose end-points are *end1Ptr and *end2Ptr to the point
 *	given by *pointPtr.
 *
 * Side effects:
 *	None.
 *
 *--------------------------------------------------------------
 */

double
TkLineToPoint(end1Ptr, end2Ptr, pointPtr)
    double end1Ptr[2];		/* Coordinates of first end-point of line. */
    double end2Ptr[2];		/* Coordinates of second end-point of line. */
    double pointPtr[2];		/* Points to coords for point. */
{
    double x, y;

    /*
     * Compute the point on the line that is closest to the
     * point.  This must be done separately for vertical edges,
     * horizontal edges, and other edges.
     */

    if (end1Ptr[0] == end2Ptr[0]) {

	/*
	 * Vertical edge.
	 */

	x = end1Ptr[0];
	if (end1Ptr[1] >= end2Ptr[1]) {
	    y = MIN(end1Ptr[1], pointPtr[1]);
	    y = MAX(y, end2Ptr[1]);
	} else {
	    y = MIN(end2Ptr[1], pointPtr[1]);
	    y = MAX(y, end1Ptr[1]);
	}
    } else if (end1Ptr[1] == end2Ptr[1]) {

	/*
	 * Horizontal edge.
	 */

	y = end1Ptr[1];
	if (end1Ptr[0] >= end2Ptr[0]) {
	    x = MIN(end1Ptr[0], pointPtr[0]);
	    x = MAX(x, end2Ptr[0]);
	} else {
	    x = MIN(end2Ptr[0], pointPtr[0]);
	    x = MAX(x, end1Ptr[0]);
	}
    } else {
	double m1, b1, m2, b2;

	/*
	 * The edge is neither horizontal nor vertical.  Convert the
	 * edge to a line equation of the form y = m1*x + b1.  Then
	 * compute a line perpendicular to this edge but passing
	 * through the point, also in the form y = m2*x + b2.
	 */

	m1 = (end2Ptr[1] - end1Ptr[1])/(end2Ptr[0] - end1Ptr[0]);
	b1 = end1Ptr[1] - m1*end1Ptr[0];
	m2 = -1.0/m1;
	b2 = pointPtr[1] - m2*pointPtr[0];
	x = (b2 - b1)/(m1 - m2);
	y = m1*x + b1;
	if (end1Ptr[0] > end2Ptr[0]) {
	    if (x > end1Ptr[0]) {
		x = end1Ptr[0];
		y = end1Ptr[1];
	    } else if (x < end2Ptr[0]) {
		x = end2Ptr[0];
		y = end2Ptr[1];
	    }
	} else {
	    if (x > end2Ptr[0]) {
		x = end2Ptr[0];
		y = end2Ptr[1];
	    } else if (x < end1Ptr[0]) {
		x = end1Ptr[0];
		y = end1Ptr[1];
	    }
	}
    }

    /*
     * Compute the distance to the closest point.
     */

    return hypot(pointPtr[0] - x, pointPtr[1] - y);
}
\f
/*
 *--------------------------------------------------------------
 *
 * TkLineToArea --
 *
 *	Determine whether a line lies entirely inside, entirely
 *	outside, or overlapping a given rectangular area.
 *
 * Results:
 *	-1 is returned if the line given by end1Ptr and end2Ptr
 *	is entirely outside the rectangle given by rectPtr.  0 is
 *	returned if the polygon overlaps the rectangle, and 1 is
 *	returned if the polygon is entirely inside the rectangle.
 *
 * Side effects:
 *	None.
 *
 *--------------------------------------------------------------
 */

int
TkLineToArea(end1Ptr, end2Ptr, rectPtr)
    double end1Ptr[2];		/* X and y coordinates for one endpoint
				 * of line. */
    double end2Ptr[2];		/* X and y coordinates for other endpoint
				 * of line. */
    double rectPtr[4];		/* Points to coords for rectangle, in the
				 * order x1, y1, x2, y2.  X1 must be no
				 * larger than x2, and y1 no larger than y2. */
{
    int inside1, inside2;

    /*
     * First check the two points individually to see whether they
     * are inside the rectangle or not.
     */

    inside1 = (end1Ptr[0] >= rectPtr[0]) && (end1Ptr[0] <= rectPtr[2])
	    && (end1Ptr[1] >= rectPtr[1]) && (end1Ptr[1] <= rectPtr[3]);
    inside2 = (end2Ptr[0] >= rectPtr[0]) && (end2Ptr[0] <= rectPtr[2])
	    && (end2Ptr[1] >= rectPtr[1]) && (end2Ptr[1] <= rectPtr[3]);
    if (inside1 != inside2) {
	return 0;
    }
    if (inside1 & inside2) {
	return 1;
    }

    /*
     * Both points are outside the rectangle, but still need to check
     * for intersections between the line and the rectangle.  Horizontal
     * and vertical lines are particularly easy, so handle them
     * separately.
     */

    if (end1Ptr[0] == end2Ptr[0]) {
	/*
	 * Vertical line.
	 */
    
	if (((end1Ptr[1] >= rectPtr[1]) ^ (end2Ptr[1] >= rectPtr[1]))
		&& (end1Ptr[0] >= rectPtr[0])
		&& (end1Ptr[0] <= rectPtr[2])) {
	    return 0;
	}
    } else if (end1Ptr[1] == end2Ptr[1]) {
	/*
	 * Horizontal line.
	 */
    
	if (((end1Ptr[0] >= rectPtr[0]) ^ (end2Ptr[0] >= rectPtr[0]))
		&& (end1Ptr[1] >= rectPtr[1])
		&& (end1Ptr[1] <= rectPtr[3])) {
	    return 0;
	}
    } else {
	double m, x, y, low, high;
    
	/*
	 * Diagonal line.  Compute slope of line and use
	 * for intersection checks against each of the
	 * sides of the rectangle: left, right, bottom, top.
	 */
    
	m = (end2Ptr[1] - end1Ptr[1])/(end2Ptr[0] - end1Ptr[0]);
	if (end1Ptr[0] < end2Ptr[0]) {
	    low = end1Ptr[0];  high = end2Ptr[0];
	} else {
	    low = end2Ptr[0]; high = end1Ptr[0];
	}
    
	/*
	 * Left edge.
	 */
    
	y = end1Ptr[1] + (rectPtr[0] - end1Ptr[0])*m;
	if ((rectPtr[0] >= low) && (rectPtr[0] <= high)
		&& (y >= rectPtr[1]) && (y <= rectPtr[3])) {
	    return 0;
	}
    
	/*
	 * Right edge.
	 */
    
	y += (rectPtr[2] - rectPtr[0])*m;
	if ((y >= rectPtr[1]) && (y <= rectPtr[3])
		&& (rectPtr[2] >= low) && (rectPtr[2] <= high)) {
	    return 0;
	}
    
	/*
	 * Bottom edge.
	 */
    
	if (end1Ptr[1] < end2Ptr[1]) {
	    low = end1Ptr[1];  high = end2Ptr[1];
	} else {
	    low = end2Ptr[1]; high = end1Ptr[1];
	}
	x = end1Ptr[0] + (rectPtr[1] - end1Ptr[1])/m;
	if ((x >= rectPtr[0]) && (x <= rectPtr[2])
		&& (rectPtr[1] >= low) && (rectPtr[1] <= high)) {
	    return 0;
	}
    
	/*
	 * Top edge.
	 */
    
	x += (rectPtr[3] - rectPtr[1])/m;
	if ((x >= rectPtr[0]) && (x <= rectPtr[2])
		&& (rectPtr[3] >= low) && (rectPtr[3] <= high)) {
	    return 0;
	}
    }
    return -1;
}
\f
/*
 *--------------------------------------------------------------
 *
 * TkPolygonToPoint --
 *
 *	Compute the distance from a point to a polygon.
 *
 * Results:
 *	The return value is 0.0 if the point referred to by
 *	pointPtr is within the polygon referred to by polyPtr
 *	and numPoints.  Otherwise the return value is the
 *	distance of the point from the polygon.
 *
 * Side effects:
 *	None.
 *
 *--------------------------------------------------------------
 */

double
TkPolygonToPoint(polyPtr, numPoints, pointPtr)
    double *polyPtr;		/* Points to an array coordinates for
				 * closed polygon:  x0, y0, x1, y1, ...
				 * The polygon may be self-intersecting. */
    int numPoints;		/* Total number of points at *polyPtr. */
    double *pointPtr;		/* Points to coords for point. */
{
    double bestDist;		/* Closest distance between point and
				 * any edge in polygon. */
    int intersections;		/* Number of edges in the polygon that
				 * intersect a ray extending vertically
				 * upwards from the point to infinity. */
    int count;
    register double *pPtr;

    /*
     * Iterate through all of the edges in the polygon, updating
     * bestDist and intersections.
     *
     * TRICKY POINT:  when computing intersections, include left
     * x-coordinate of line within its range, but not y-coordinate.
     * Otherwise if the point lies exactly below a vertex we'll
     * count it as two intersections.
     */

    bestDist = 1.0e40;
    intersections = 0;

    for (count = numPoints, pPtr = polyPtr; count > 1; count--, pPtr += 2) {
	double x, y, dist;

	/*
	 * Compute the point on the current edge closest to the point
	 * and update the intersection count.  This must be done
	 * separately for vertical edges, horizontal edges, and
	 * other edges.
	 */

	if (pPtr[2] == pPtr[0]) {

	    /*
	     * Vertical edge.
	     */

	    x = pPtr[0];
	    if (pPtr[1] >= pPtr[3]) {
		y = MIN(pPtr[1], pointPtr[1]);
		y = MAX(y, pPtr[3]);
	    } else {
		y = MIN(pPtr[3], pointPtr[1]);
		y = MAX(y, pPtr[1]);
	    }
	} else if (pPtr[3] == pPtr[1]) {

	    /*
	     * Horizontal edge.
	     */

	    y = pPtr[1];
	    if (pPtr[0] >= pPtr[2]) {
		x = MIN(pPtr[0], pointPtr[0]);
		x = MAX(x, pPtr[2]);
		if ((pointPtr[1] < y) && (pointPtr[0] < pPtr[0])
			&& (pointPtr[0] >= pPtr[2])) {
		    intersections++;
		}
	    } else {
		x = MIN(pPtr[2], pointPtr[0]);
		x = MAX(x, pPtr[0]);
		if ((pointPtr[1] < y) && (pointPtr[0] < pPtr[2])
			&& (pointPtr[0] >= pPtr[0])) {
		    intersections++;
		}
	    }
	} else {
	    double m1, b1, m2, b2;
	    int lower;			/* Non-zero means point below line. */

	    /*
	     * The edge is neither horizontal nor vertical.  Convert the
	     * edge to a line equation of the form y = m1*x + b1.  Then
	     * compute a line perpendicular to this edge but passing
	     * through the point, also in the form y = m2*x + b2.
	     */

	    m1 = (pPtr[3] - pPtr[1])/(pPtr[2] - pPtr[0]);
	    b1 = pPtr[1] - m1*pPtr[0];
	    m2 = -1.0/m1;
	    b2 = pointPtr[1] - m2*pointPtr[0];
	    x = (b2 - b1)/(m1 - m2);
	    y = m1*x + b1;
	    if (pPtr[0] > pPtr[2]) {
		if (x > pPtr[0]) {
		    x = pPtr[0];
		    y = pPtr[1];
		} else if (x < pPtr[2]) {
		    x = pPtr[2];
		    y = pPtr[3];
		}
	    } else {
		if (x > pPtr[2]) {
		    x = pPtr[2];
		    y = pPtr[3];
		} else if (x < pPtr[0]) {
		    x = pPtr[0];
		    y = pPtr[1];
		}
	    }
	    lower = (m1*pointPtr[0] + b1) > pointPtr[1];
	    if (lower && (pointPtr[0] >= MIN(pPtr[0], pPtr[2]))
		    && (pointPtr[0] < MAX(pPtr[0], pPtr[2]))) {
		intersections++;
	    }
	}

	/*
	 * Compute the distance to the closest point, and see if that
	 * is the best distance seen so far.
	 */

	dist = hypot(pointPtr[0] - x, pointPtr[1] - y);
	if (dist < bestDist) {
	    bestDist = dist;
	}
    }

    /*
     * We've processed all of the points.  If the number of intersections
     * is odd, the point is inside the polygon.
     */

    if (intersections & 0x1) {
	return 0.0;
    }
    return bestDist;
}
\f
/*
 *--------------------------------------------------------------
 *
 * TkPolygonToArea --
 *
 *	Determine whether a polygon lies entirely inside, entirely
 *	outside, or overlapping a given rectangular area.
 *
 * Results:
 *	-1 is returned if the polygon given by polyPtr and numPoints
 *	is entirely outside the rectangle given by rectPtr.  0 is
 *	returned if the polygon overlaps the rectangle, and 1 is
 *	returned if the polygon is entirely inside the rectangle.
 *
 * Side effects:
 *	None.
 *
 *--------------------------------------------------------------
 */

int
TkPolygonToArea(polyPtr, numPoints, rectPtr)
    double *polyPtr;		/* Points to an array coordinates for
				 * closed polygon:  x0, y0, x1, y1, ...
				 * The polygon may be self-intersecting. */
    int numPoints;		/* Total number of points at *polyPtr. */
    register double *rectPtr;	/* Points to coords for rectangle, in the
				 * order x1, y1, x2, y2.  X1 and y1 must
				 * be lower-left corner. */
{
    int state;			/* State of all edges seen so far (-1 means
				 * outside, 1 means inside, won't ever be
				 * 0). */
    int count;
    register double *pPtr;

    /*
     * Iterate over all of the edges of the polygon and test them
     * against the rectangle.  Can quit as soon as the state becomes
     * "intersecting".
     */

    state = TkLineToArea(polyPtr, polyPtr+2, rectPtr);
    if (state == 0) {
	return 0;
    }
    for (pPtr = polyPtr+2, count = numPoints-1; count >= 2;
	    pPtr += 2, count--) {
	if (TkLineToArea(pPtr, pPtr+2, rectPtr) != state) {
	    return 0;
	}
    }

    /*
     * If all of the edges were inside the rectangle we're done.
     * If all of the edges were outside, then the rectangle could
     * still intersect the polygon (if it's entirely enclosed).
     * Call TkPolygonToPoint to figure this out.
     */

    if (state == 1) {
	return 1;
    }
    if (TkPolygonToPoint(polyPtr, numPoints, rectPtr) == 0.0) {
	return 0;
    }
    return -1;
}
\f
/*
 *--------------------------------------------------------------
 *
 * TkOvalToPoint --
 *
 *	Computes the distance from a given point to a given
 *	oval, in canvas units.
 *
 * Results:
 *	The return value is 0 if the point given by *pointPtr is
 *	inside the oval.  If the point isn't inside the
 *	oval then the return value is approximately the distance
 *	from the point to the oval.  If the oval is filled, then
 *	anywhere in the interior is considered "inside";  if
 *	the oval isn't filled, then "inside" means only the area
 *	occupied by the outline.
 *
 * Side effects:
 *	None.
 *
 *--------------------------------------------------------------
 */

	/* ARGSUSED */
double
TkOvalToPoint(ovalPtr, width, filled, pointPtr)
    double ovalPtr[4];		/* Pointer to array of four coordinates
				 * (x1, y1, x2, y2) defining oval's bounding
				 * box. */
    double width;		/* Width of outline for oval. */
    int filled;			/* Non-zero means oval should be treated as
				 * filled;  zero means only consider outline. */
    double pointPtr[2];		/* Coordinates of point. */
{
    double xDelta, yDelta, scaledDistance, distToOutline, distToCenter;

    /*
     * Compute the distance between the center of the oval and the
     * point in question, using a coordinate system where the oval
     * has been transformed to a circle with unit radius.
     */

    xDelta = (pointPtr[0] - (ovalPtr[0] + ovalPtr[2])/2.0);
    yDelta = (pointPtr[1] - (ovalPtr[1] + ovalPtr[3])/2.0);
    distToCenter = hypot(xDelta, yDelta);
    scaledDistance = hypot(xDelta / ((ovalPtr[2] + width - ovalPtr[0])/2.0),
	    yDelta / ((ovalPtr[3] + width - ovalPtr[1])/2.0));


    /*
     * If the scaled distance is greater than 1 then it means no
     * hit.  Compute the distance from the point to the edge of
     * the circle, then scale this distance back to the original
     * coordinate system.
     *
     * Note: this distance isn't completely accurate.  It's only
     * an approximation, and it can overestimate the correct
     * distance when the oval is eccentric.
     */

    if (scaledDistance > 1.0) {
	return (distToCenter/scaledDistance) * (scaledDistance - 1.0);
    }

    /*
     * Scaled distance less than 1 means the point is inside the
     * outer edge of the oval.  If this is a filled oval, then we
     * have a hit.  Otherwise, do the same computation as above
     * (scale back to original coordinate system), but also check
     * to see if the point is within the width of the outline.
     */

    if (filled) {
	return 0.0;
    }
    distToOutline = (distToCenter/scaledDistance) * (1.0 - scaledDistance)
	    - width;
    if (distToOutline < 0.0) {
	return 0.0;
    }
    return distToOutline;
}
\f
/*
 *--------------------------------------------------------------
 *
 * TkOvalToArea --
 *
 *	Determine whether an oval lies entirely inside, entirely
 *	outside, or overlapping a given rectangular area.
 *
 * Results:
 *	-1 is returned if the oval described by ovalPtr is entirely
 *	outside the rectangle given by rectPtr.  0 is returned if the
 *	oval overlaps the rectangle, and 1 is returned if the oval
 *	is entirely inside the rectangle.
 *
 * Side effects:
 *	None.
 *
 *--------------------------------------------------------------
 */

int
TkOvalToArea(ovalPtr, rectPtr)
    register double *ovalPtr;	/* Points to coordinates definining the
				 * bounding rectangle for the oval: x1, y1,
				 * x2, y2.  X1 must be less than x2 and y1
				 * less than y2. */
    register double *rectPtr;	/* Points to coords for rectangle, in the
				 * order x1, y1, x2, y2.  X1 and y1 must
				 * be lower-left corner. */
{
    double centerX, centerY, radX, radY, deltaX, deltaY;

    /*
     * First, see if oval is entirely inside rectangle or entirely
     * outside rectangle.
     */

    if ((rectPtr[0] <= ovalPtr[0]) && (rectPtr[2] >= ovalPtr[2])
	    && (rectPtr[1] <= ovalPtr[1]) && (rectPtr[3] >= ovalPtr[3])) {
	return 1;
    }
    if ((rectPtr[2] < ovalPtr[0]) || (rectPtr[0] > ovalPtr[2])
	    || (rectPtr[3] < ovalPtr[1]) || (rectPtr[1] > ovalPtr[3])) {
	return -1;
    }

    /*
     * Next, go through the rectangle side by side.  For each side
     * of the rectangle, find the point on the side that is closest
     * to the oval's center, and see if that point is inside the
     * oval.  If at least one such point is inside the oval, then
     * the rectangle intersects the oval.
     */

    centerX = (ovalPtr[0] + ovalPtr[2])/2;
    centerY = (ovalPtr[1] + ovalPtr[3])/2;
    radX = (ovalPtr[2] - ovalPtr[0])/2;
    radY = (ovalPtr[3] - ovalPtr[1])/2;

    deltaY = rectPtr[1] - centerY;
    if (deltaY < 0.0) {
	deltaY = centerY - rectPtr[3];
	if (deltaY < 0.0) {
	    deltaY = 0;
	}
    }
    deltaY /= radY;
    deltaY *= deltaY;

    /*
     * Left side:
     */

    deltaX = (rectPtr[0] - centerX)/radX;
    deltaX *= deltaX;
    if ((deltaX + deltaY) <= 1.0) {
	return 0;
    }

    /*
     * Right side:
     */

    deltaX = (rectPtr[2] - centerX)/radX;
    deltaX *= deltaX;
    if ((deltaX + deltaY) <= 1.0) {
	return 0;
    }

    deltaX = rectPtr[0] - centerX;
    if (deltaX < 0.0) {
	deltaX = centerX - rectPtr[2];
	if (deltaX < 0.0) {
	    deltaX = 0;
	}
    }
    deltaX /= radX;
    deltaX *= deltaX;

    /*
     * Bottom side:
     */

    deltaY = (rectPtr[1] - centerY)/radY;
    deltaY *= deltaY;
    if ((deltaX + deltaY) < 1.0) {
	return 0;
    }

    /*
     * Top side:
     */

    deltaY = (rectPtr[3] - centerY)/radY;
    deltaY *= deltaY;
    if ((deltaX + deltaY) < 1.0) {
	return 0;
    }

    return -1;
}
\f
/*
 *--------------------------------------------------------------
 *
 * TkIncludePoint --
 *
 *	Given a point and a generic canvas item header, expand
 *	the item's bounding box if needed to include the point.
 *
 * Results:
 *	None.
 *
 * Side effects:
 *	The boudn.
 *
 *--------------------------------------------------------------
 */

	/* ARGSUSED */
void
TkIncludePoint(canvasPtr, itemPtr, pointPtr)
    Tk_Canvas *canvasPtr;		/* Canvas containing item. */
    register Tk_Item *itemPtr;		/* Item whose bounding box is
					 * being calculated. */
    double *pointPtr;			/* Address of two doubles giving
					 * x and y coordinates of point. */
{
    int tmp;

    tmp = pointPtr[0] + 0.5;
    if (tmp < itemPtr->x1) {
	itemPtr->x1 = tmp;
    }
    if (tmp > itemPtr->x2) {
	itemPtr->x2 = tmp;
    }
    tmp = pointPtr[1] + 0.5;
    if (tmp < itemPtr->y1) {
	itemPtr->y1 = tmp;
    }
    if (tmp > itemPtr->y2) {
	itemPtr->y2 = tmp;
    }
}
\f
/*
 *--------------------------------------------------------------
 *
 * TkBezierScreenPoints --
 *
 *	Given four control points, create a larger set of XPoints
 *	for a Bezier spline based on the points.
 *
 * Results:
 *	The array at *xPointPtr gets filled in with numSteps XPoints
 *	corresponding to the Bezier spline defined by the four 
 *	control points.  Note:  no output point is generated for the
 *	first input point, but an output point *is* generated for
 *	the last input point.
 *
 * Side effects:
 *	None.
 *
 *--------------------------------------------------------------
 */

void
TkBezierScreenPoints(canvasPtr, control, numSteps, xPointPtr)
    Tk_Canvas *canvasPtr;		/* Canvas in which curve is to be
					 * drawn. */
    double control[];			/* Array of coordinates for four
					 * control points:  x0, y0, x1, y1,
					 * ... x3 y3. */
    int numSteps;			/* Number of curve points to
					 * generate.  */
    register XPoint *xPointPtr;		/* Where to put new points. */
{
    int i;
    double u, u2, u3, t, t2, t3;

    for (i = 1; i <= numSteps; i++, xPointPtr++) {
	t = ((double) i)/((double) numSteps);
	t2 = t*t;
	t3 = t2*t;
	u = 1.0 - t;
	u2 = u*u;
	u3 = u2*u;
	xPointPtr->x = SCREEN_X(canvasPtr, (control[0]*u3
		+ 3.0 * (control[2]*t*u2 + control[4]*t2*u) + control[6]*t3));
	xPointPtr->y = SCREEN_Y(canvasPtr, (control[1]*u3
		+ 3.0 * (control[3]*t*u2 + control[5]*t2*u) + control[7]*t3));
    }
}
\f
/*
 *--------------------------------------------------------------
 *
 * TkBezierPoints --
 *
 *	Given four control points, create a larger set of points
 *	for a Bezier spline based on the points.
 *
 * Results:
 *	The array at *coordPtr gets filled in with 2*numSteps
 *	coordinates, which correspond to the Bezier spline defined
 *	by the four control points.  Note:  no output point is
 *	generated for the first input point, but an output point
 *	*is* generated for the last input point.
 *
 * Side effects:
 *	None.
 *
 *--------------------------------------------------------------
 */

void
TkBezierPoints(control, numSteps, coordPtr)
    double control[];			/* Array of coordinates for four
					 * control points:  x0, y0, x1, y1,
					 * ... x3 y3. */
    int numSteps;			/* Number of curve points to
					 * generate.  */
    register double *coordPtr;		/* Where to put new points. */
{
    int i;
    double u, u2, u3, t, t2, t3;

    for (i = 1; i <= numSteps; i++, coordPtr += 2) {
	t = ((double) i)/((double) numSteps);
	t2 = t*t;
	t3 = t2*t;
	u = 1.0 - t;
	u2 = u*u;
	u3 = u2*u;
	coordPtr[0] = control[0]*u3
		+ 3.0 * (control[2]*t*u2 + control[4]*t2*u) + control[6]*t3;
	coordPtr[1] = control[1]*u3
		+ 3.0 * (control[3]*t*u2 + control[5]*t2*u) + control[7]*t3;
    }
}
\f
/*
 *--------------------------------------------------------------
 *
 * TkMakeBezierCurve --
 *
 *	Given a set of points, create a new set of points that
 *	fit Bezier splines to the line segments connecting the
 *	original points.  Produces output points in either of two
 *	forms.
 *
 * Results:
 *	Either or both of the xPoints or dblPoints arrays are filled
 *	in.  The return value is the number of points placed in the
 *	arrays.  Note:  if the first and last points are the same, then
 *	a closed curve is generated.
 *
 * Side effects:
 *	None.
 *
 *--------------------------------------------------------------
 */

int
TkMakeBezierCurve(canvasPtr, pointPtr, numPoints, numSteps, xPoints, dblPoints)
    Tk_Canvas *canvasPtr;		/* Canvas in which curve is to be
					 * drawn. */
    double *pointPtr;			/* Array of input coordinates:  x0,
					 * y0, x1, y1, etc.. */
    int numPoints;			/* Number of points at pointPtr. */
    int numSteps;			/* Number of steps to use for each
					 * spline segments (determines
					 * smoothness of curve). */
    XPoint xPoints[];			/* Array of XPoints to fill in (e.g.
					 * for display.  NULL means don't
					 * fill in any XPoints. */
    double dblPoints[];			/* Array of points to fill in as
					 * doubles, in the form x0, y0,
					 * x1, y1, ....  NULL means don't
					 * fill in anything in this form. 
					 * Caller must make sure that this
					 * array has enough space. */
{
    int closed, outputPoints, i;
    int numCoords = numPoints*2;
    double control[8];

    /*
     * If the curve is a closed one then generate a special spline
     * that spans the last points and the first ones.  Otherwise
     * just put the first point into the output.
     */

    outputPoints = 0;
    if ((pointPtr[0] == pointPtr[numCoords-2])
	    && (pointPtr[1] == pointPtr[numCoords-1])) {
	closed = 1;
	control[0] = 0.5*pointPtr[numCoords-4] + 0.5*pointPtr[0];
	control[1] = 0.5*pointPtr[numCoords-3] + 0.5*pointPtr[1];
	control[2] = 0.167*pointPtr[numCoords-4] + 0.833*pointPtr[0];
	control[3] = 0.167*pointPtr[numCoords-3] + 0.833*pointPtr[1];
	control[4] = 0.833*pointPtr[0] + 0.167*pointPtr[2];
	control[5] = 0.833*pointPtr[1] + 0.167*pointPtr[3];
	control[6] = 0.5*pointPtr[0] + 0.5*pointPtr[2];
	control[7] = 0.5*pointPtr[1] + 0.5*pointPtr[3];
	if (xPoints != NULL) {
	    xPoints->x = SCREEN_X(canvasPtr, control[0]);
	    xPoints->y = SCREEN_Y(canvasPtr, control[1]);
	    TkBezierScreenPoints(canvasPtr, control, numSteps, xPoints+1);
	    xPoints += numSteps+1;
	}
	if (dblPoints != NULL) {
	    dblPoints[0] = control[0];
	    dblPoints[1] = control[1];
	    TkBezierPoints(control, numSteps, dblPoints+2);
	    dblPoints += 2*(numSteps+1);
	}
	outputPoints += numSteps+1;
    } else {
	closed = 0;
	if (xPoints != NULL) {
	    xPoints->x = SCREEN_X(canvasPtr, pointPtr[0]);
	    xPoints->y = SCREEN_Y(canvasPtr, pointPtr[1]);
	    xPoints += 1;
	}
	if (dblPoints != NULL) {
	    dblPoints[0] = pointPtr[0];
	    dblPoints[1] = pointPtr[1];
	    dblPoints += 2;
	}
	outputPoints += 1;
    }

    for (i = 2; i < numPoints; i++, pointPtr += 2) {
	/*
	 * Set up the first two control points.  This is done
	 * differently for the first spline of an open curve
	 * than for other cases.
	 */

	if ((i == 2) && !closed) {
	    control[0] = pointPtr[0];
	    control[1] = pointPtr[1];
	    control[2] = 0.333*pointPtr[0] + 0.667*pointPtr[2];
	    control[3] = 0.333*pointPtr[1] + 0.667*pointPtr[3];
	} else {
	    control[0] = 0.5*pointPtr[0] + 0.5*pointPtr[2];
	    control[1] = 0.5*pointPtr[1] + 0.5*pointPtr[3];
	    control[2] = 0.167*pointPtr[0] + 0.833*pointPtr[2];
	    control[3] = 0.167*pointPtr[1] + 0.833*pointPtr[3];
	}

	/*
	 * Set up the last two control points.  This is done
	 * differently for the last spline of an open curve
	 * than for other cases.
	 */

	if ((i == (numPoints-1)) && !closed) {
	    control[4] = .667*pointPtr[2] + .333*pointPtr[4];
	    control[5] = .667*pointPtr[3] + .333*pointPtr[5];
	    control[6] = pointPtr[4];
	    control[7] = pointPtr[5];
	} else {
	    control[4] = .833*pointPtr[2] + .167*pointPtr[4];
	    control[5] = .833*pointPtr[3] + .167*pointPtr[5];
	    control[6] = 0.5*pointPtr[2] + 0.5*pointPtr[4];
	    control[7] = 0.5*pointPtr[3] + 0.5*pointPtr[5];
	}

	/*
	 * If the first two points coincide, or if the last
	 * two points coincide, then generate a single
	 * straight-line segment by outputting the last control
	 * point.
	 */

	if (((pointPtr[0] == pointPtr[2]) && (pointPtr[1] == pointPtr[3]))
		|| ((pointPtr[2] == pointPtr[4])
		&& (pointPtr[3] == pointPtr[5]))) {
	    if (xPoints != NULL) {
		xPoints[0].x = SCREEN_X(canvasPtr, control[6]);
		xPoints[0].y = SCREEN_Y(canvasPtr, control[7]);
		xPoints++;
	    }
	    if (dblPoints != NULL) {
		dblPoints[0] = control[6];
		dblPoints[1] = control[7];
		dblPoints += 2;
	    }
	    outputPoints += 1;
	    continue;
	}

	/*
	 * Generate a Bezier spline using the control points.
	 */


	if (xPoints != NULL) {
	    TkBezierScreenPoints(canvasPtr, control, numSteps, xPoints);
	    xPoints += numSteps;
	}
	if (dblPoints != NULL) {
	    TkBezierPoints(control, numSteps, dblPoints);
	    dblPoints += 2*numSteps;
	}
	outputPoints += numSteps;
    }
    return outputPoints;
}
\f
/*
 *--------------------------------------------------------------
 *
 * TkGetMiterPoints --
 *
 *	Given three points forming an angle, compute the
 *	coordinates of the inside and outside points of
 *	the mitered corner formed by a line of a given
 *	width at that angle.
 *
 * Results:
 *	If the angle formed by the three points is less than
 *	11 degrees then 0 is returned and m1 and m2 aren't
 *	modified.  Otherwise 1 is returned and the points at
 *	m1 and m2 are filled in with the positions of the points
 *	of the mitered corner.
 *
 * Side effects:
 *	None.
 *
 *--------------------------------------------------------------
 */

int
TkGetMiterPoints(p1, p2, p3, width, m1, m2)
    double p1[];		/* Points to x- and y-coordinates of point
				 * before vertex. */
    double p2[];		/* Points to x- and y-coordinates of vertex
				 * for mitered joint. */
    double p3[];		/* Points to x- and y-coordinates of point
				 * after vertex. */
    double width;		/* Width of line.  */
    double m1[];		/* Points to place to put "left" vertex
				 * point (see as you face from p1 to p2). */
    double m2[];		/* Points to place to put "right" vertex
				 * point. */
{
    double theta1;		/* Angle of segment p2-p1. */
    double theta2;		/* Angle of segment p2-p3. */
    double theta;		/* Angle between line segments (angle
				 * of joint). */
    double theta3;		/* Angle that bisects theta1 and
				 * theta2 and points to m1. */
    double dist;		/* Distance of miter points from p2. */
    double deltaX, deltaY;	/* X and y offsets cooresponding to
				 * dist (fudge factors for bounding
				 * box). */
    static float elevenDegrees = (11.0*2.0*PI)/360.0;

    if (p2[1] == p1[1]) {
	theta1 = (p2[0] < p1[0]) ? 0 : PI;
    } else if (p2[0] == p1[0]) {
	theta1 = (p2[1] < p1[1]) ? PI/2.0 : -PI/2.0;
    } else {
	theta1 = atan2(p1[1] - p2[1], p1[0] - p2[0]);
    }
    if (p3[1] == p2[1]) {
	theta2 = (p3[0] > p2[0]) ? 0 : PI;
    } else if (p3[0] == p2[0]) {
	theta2 = (p3[1] > p2[1]) ? PI/2.0 : -PI/2.0;
    } else {
	theta2 = atan2(p3[1] - p2[1], p3[0] - p2[0]);
    }
    theta = theta1 - theta2;
    if (theta > PI) {
	theta -= 2*PI;
    } else if (theta < -PI) {
	theta += 2*PI;
    }
    if ((theta < elevenDegrees) && (theta > -elevenDegrees)) {
	return 0;
    }
    dist = 0.5*width/sin(0.5*theta);
    if (dist < 0.0) {
	dist = -dist;
    }

    /*
     * Compute theta3 (make sure that it points to the left when
     * looking from p1 to p2).
     */

    theta3 = (theta1 + theta2)/2.0;
    if (sin(theta3 - (theta1 + PI)) < 0.0) {
	theta3 += PI;
    }
    deltaX = dist*cos(theta3);
    m1[0] = p2[0] + deltaX;
    m2[0] = p2[0] - deltaX;
    deltaY = dist*sin(theta3);
    m1[1] = p2[1] + deltaY;
    m2[1] = p2[1] - deltaY;
    return 1;
}
\f
/*
 *--------------------------------------------------------------
 *
 * TkGetButtPoints --
 *
 *	Given two points forming a line segment, compute the
 *	coordinates of two endpoints of a rectangle formed by
 *	bloating the line segment until it is width units wide.
 *
 * Results:
 *	There is no return value.  M1 and m2 are filled in to
 *	correspond to m1 and m2 in the diagram below:
 *
 *		   ----------------* m1
 *				   |
 *		p1 *---------------* p2
 *				   |
 *		   ----------------* m2
 *
 *	M1 and m2 will be W units apart, with p2 centered between
 *	them and m1-m2 perpendicular to p1-p2.  However, if
 *	"project" is true then m1 and m2 will be as follows:
 *
 *		   -------------------* m1
 *				  p2  |
 *		p1 *---------------*  |
 *				      |
 *		   -------------------* m2
 *
 *	In this case p2 will be width/2 units from the segment m1-m2.
 *
 * Side effects:
 *	None.
 *
 *--------------------------------------------------------------
 */

void
TkGetButtPoints(p1, p2, width, project, m1, m2)
    double p1[];		/* Points to x- and y-coordinates of point
				 * before vertex. */
    double p2[];		/* Points to x- and y-coordinates of vertex
				 * for mitered joint. */
    double width;		/* Width of line.  */
    int project;		/* Non-zero means project p2 by an additional
				 * width/2 before computing m1 and m2. */
    double m1[];		/* Points to place to put "left" result
				 * point, as you face from p1 to p2. */
    double m2[];		/* Points to place to put "right" result
				 * point. */
{
    double length;		/* Length of p1-p2 segment. */
    double deltaX, deltaY;	/* Increments in coords. */

    width *= 0.5;
    length = hypot(p2[0] - p1[0], p2[1] - p1[1]);
    if (length == 0.0) {
	m1[0] = m2[0] = p2[0];
	m1[1] = m2[1] = p2[1];
    } else {
	deltaX = -width * (p2[1] - p1[1]) / length;
	deltaY = width * (p2[0] - p1[0]) / length;
	m1[0] = p2[0] + deltaX;
	m2[0] = p2[0] - deltaX;
	m1[1] = p2[1] + deltaY;
	m2[1] = p2[1] - deltaY;
	if (project) {
	    m1[0] += deltaY;
	    m2[0] += deltaY;
	    m1[1] -= deltaX;
	    m2[1] -= deltaX;
	}
    }
}