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csrarea.c
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C/C++ Source or Header
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1990-04-20
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6KB
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187 lines
#ifndef lint
static char SccsId[] = "%W% %G%";
#endif
/* Module: csrarea.c (Cursor Area)
* Purpose: Calculate areas of cursors
* Subroutine: cursor_area(); returns: double
* Copyright: 1989 Smithsonian Astrophysical Observatory
* You may do anything you like with this file except remove
* this copyright. The Smithsonian Astrophysical Observatory
* makes no representations about the suitability of this
* software for any purpose. It is provided "as is" without
* express or implied warranty.
* Modified: {0} Michael VanHilst initial version 4 June 1989
* {n} <who> -- <does what> -- <when>
*/
#include <X11/Xlib.h> /* X window stuff */
#include <X11/Xutil.h> /* X window manager stuff */
#include "hfiles/color.h" /* cursor colors needed by Cursor.h */
#include "hfiles/constant.h" /* define codes */
#include "hfiles/cursor.h" /* define cursor parameter structures */
#define PI 3.14159265358979323846
/*
* Subroutine: cursor_area
* Purpose: Calculate area, in float units file pixels, enclosed by cursor
* Method: Use mathematical formula appropriate to cursor type
*/
double cursor_area ( cursor, user_info )
struct cursorRec *cursor;
int user_info; /* flag, data is for user info */
{
double area;
int i, j;
static int test_cross();
switch( cursor->type ) {
case COP_Circle:
area = PI * cursor->file.Xdim * cursor->file.Xdim;
break;
case COP_Ellipse:
area = PI * cursor->file.Xdim * cursor->file.Ydim;
break;
case COP_Box:
area = cursor->file.Xdim * cursor->file.Ydim * 4.0;
break;
case COP_Point:
area = 0.0;
break;
case COP_Polygon:
/* polygon area is sum of signed areas between each edge and x axis */
/* (except when polygon edges cross one another) */
area = 0;
if( user_info &&
test_cross(cursor->poly, cursor->poly_cnt, cursor->poly_cnt - 1, 0) )
return( -1.0 );
j = cursor->poly_cnt - 1;
/* each area is (x1-x2)*(y1+y2)/2, /2 will be done once at end */
for( i=0; i<cursor->poly_cnt; i++ ) {
area += (cursor->poly[i].fileX - cursor->poly[j].fileX) *
(cursor->poly[i].fileY + cursor->poly[j].fileY);
j = i;
}
/* sign of area depends on clockwise or counter-clockwise ordering */
if( area < 0.0 ) area *= -0.5;
else area *= 0.5;
default:
break;
}
return( area );
}
/* end points of a polygon edge against which to test others for crossing */
static double x11, y11, x12, y12;
/*
* Subroutine: test_cross
* Purpose: Test the edges of a polygon to see if any cross each other
* method: Starting with last edge, test each edge against subsequent
* edges. Routine recurses with for next edge. Adjacent edges
* are not tested since neighbors cannot cross but neighbors do
* share a common point.
*/
static int test_cross ( pt, cnt, j, i )
PolyPoint *pt; /* list of vertices */
int cnt; /* number of vertices */
int j, i; /* two vertices at ends of edge being tested */
{
int k;
static int intercept();
if( (i+2) >= cnt ) {
return( 0 );
} else {
x11 = pt[j].fileX;
y11 = pt[j].fileY;
x12 = pt[i].fileX;
y12 = pt[i].fileY;
/* test each subsequent edge against this edge (but not adjacent edges) */
for( k=i+2; k<cnt; k++ ) {
if( ((k+1) != j) &&
intercept(pt[k-1].fileX, pt[k-1].fileY, pt[k].fileX, pt[k].fileY) )
return(1);
}
/* recurse on to test next edge */
return( test_cross(pt, cnt, i, i+1) );
}
}
/*
* Subroutine: intercept
* Purpose: Test this edge against the reference edge
* Method: A) Minmax test if two edges have overlapping coordinates.
* B) Calculate the intercept of the two lines.
* C) Test if intercept is within both edges.
*/
static int intercept ( x21, y21, x22, y22 )
double x21, y21, x22, y22;
{
double xpt, ypt, m1, m2;
/* try minmax test */
if( x11 > x12 ) {
if( ((x12 >= x21) && (x12 >= x22)) || ((x11 <= x21) && (x11 <= x22)) )
return( 0 );
} else {
if( ((x11 >= x21) && (x11 >= x22)) || ((x12 <= x21) && (x12 <= x22)) )
return( 0 );
}
if( y11 > y21 ) {
if( ((y12 >= y21) && (y12 >= y22)) || ((y11 <= y21) && (y11 <= y22)) )
return( 0 );
} else {
if( ((y11 >= y21) && (y11 >= y22)) || ((y12 <= y21) && (y12 <= y22)) )
return( 0 );
}
/* compute intercept of line */
if( x12 == x11 ) {
xpt = x12;
ypt = y21 + ((xpt - x21) * (y22 - y21) / (x22 - x21));
} else if( x22 == x21 ) {
xpt = x21;
ypt = y11 + ((xpt - x11) * (y12 - y11) / (x12 - x11));
} else {
m1 = (y12 - y11) / (x12 - x11);
m2 = (y22 - y21) / (x22 - x21);
xpt = ((x11 * m1) - (x21 * m2) + (y21 - y11)) / (m1 - m2);
ypt = y11 + (m1 * (xpt - x11));
}
/* check for being on both edges */
/* intercept x within x's of reference edge */
if( x11 > x12 ) {
if( (x12 > xpt) || (xpt > x11) )
return( 0 );
} else {
if( (x12 < xpt) || (xpt < x11) )
return( 0 );
}
/* intercept y within y's of reference edge */
if( y11 > y12 ) {
if( (y12 > ypt) || (ypt > y11) )
return( 0 );
} else {
if( (y12 < ypt) || (ypt < y11) )
return( 0 );
}
/* intercept x within x's of test edge */
if( x21 > x22 ) {
if( (x22 > xpt) || (xpt > x21) )
return( 0 );
} else {
if( (x22 < xpt) || (xpt < x21) )
return( 0 );
}
/* intercept y within y's of test edge */
if( y21 > y22 ) {
if( (y22 > ypt) || (ypt > y21) )
return( 0 );
} else {
if( (y22 < ypt) || (ypt < y21) )
return( 0 );
}
return( 1 );
}