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/* Copyright (c) 1992 AT&T - All rights reserved. */
#include <libc.h>
#include <libg.h>
#include "libgint.h"
typedef struct Linedesc
{
int x0;
int y0;
char xmajor;
char slopeneg;
long dminor;
long dmajor;
} Linedesc;
int _clipline(Rectangle, Point*, Point*, Linedesc*);
#define XYswap(p) t=(p)->x, (p)->x=(p)->y, (p)->y=t
#define Swap(x, y) t=x, x=y, y=t
static long
lfloor(long x, long y) /* first integer <= x/y */
{
if(y <= 0){
if(y == 0)
return x;
y = -y;
x = -x;
}
if(x < 0){ /* be careful; C div. is undefined */
x = -x;
x += y-1;
return -(x/y);
}
return x/y;
}
static long
lceil(long x, long y) /* first integer >= x/y */
{
if(y <= 0){
if(y == 0)
return x;
y = -y;
x = -x;
}
if(x < 0){
x = -x;
return -(x/y);
}
x += y-1;
return x/y;
}
int
_gminor(long x, Linedesc *l)
{
long y;
y = 2*(x-l->x0)*l->dminor + l->dmajor;
y = lfloor(y, 2*l->dmajor) + l->y0;
return l->slopeneg? -y : y;
}
int
_gmajor(long y, Linedesc *l)
{
long x;
x = 2*((l->slopeneg? -y : y)-l->y0)*l->dmajor - l->dminor;
x = lceil(x, 2*l->dminor) + l->x0;
if(l->dminor)
while(_gminor(x-1, l) == y)
x--;
return x;
}
void
gsetline(Point *pp0, Point *pp1, Linedesc *l)
{
long dx, dy, t;
Point endpt;
int swapped;
Point p0, p1;
swapped = 0;
p0 = *pp0;
p1 = *pp1;
l->xmajor = 1;
l->slopeneg = 0;
dx = p1.x - p0.x;
dy = p1.y - p0.y;
if(abs(dy) > abs(dx)){ /* Steep */
l->xmajor = 0;
XYswap(&p0);
XYswap(&p1);
Swap(dx, dy);
}
if(dx < 0){
swapped++;
Swap(p0.x, p1.x);
Swap(p0.y, p1.y);
dx = -dx;
dy = -dy;
}
if(dy < 0){
l->slopeneg = 1;
dy = -dy;
p0.y = -p0.y;
}
l->dminor = dy;
l->dmajor = dx;
l->x0 = p0.x;
l->y0 = p0.y;
p1.x = swapped? p0.x+1 : p1.x-1;
p1.y = _gminor(p1.x, l);
if(l->xmajor == 0){
XYswap(&p0);
XYswap(&p1);
}
if(pp0->x > pp1->x){
*pp1 = *pp0;
*pp0 = p1;
}else
*pp1 = p1;
}
/*
* Modified clip-to-rectangle algorithm
* works in bitmaps
* Everything in SCREEN coordinates.
*
* Newman & Sproull 124 (1st edition)
*/
static
code(Point *p, Rectangle *r)
{
return( (p->x<r->min.x? 1 : p->x>=r->max.x? 2 : 0) |
(p->y<r->min.y? 4 : p->y>=r->max.y? 8 : 0));
}
int
clipline(Rectangle r, Point *p0, Point *p1)
{
Linedesc l;
return _clipline(r, p0, p1, &l);
}
int
_clipline(Rectangle r, Point *p0, Point *p1, Linedesc *l)
{
int c0, c1, n;
long t, ret;
Point temp;
int swapped;
if(p0->x==p1->x && p0->y==p1->y)
return 0;
gsetline(p0, p1, l);
/* line is now closed */
if(l->xmajor == 0){
XYswap(p0);
XYswap(p1);
XYswap(&r.min);
XYswap(&r.max);
}
c0 = code(p0, &r);
c1 = code(p1, &r);
ret = 1;
swapped = 0;
n = 0;
while(c0 | c1){
if(c0 & c1){ /* no point of line in r */
ret = 0;
goto Return;
}
if(++n > 10){ /* horrible points; overflow etc. etc. */
ret = 0;
goto Return;
}
if(c0 == 0){ /* swap points */
temp = *p0;
*p0 = *p1;
*p1 = temp;
Swap(c0, c1);
swapped ^= 1;
}
if(c0 == 0)
break;
if(c0 & 1){ /* push towards left edge */
p0->x = r.min.x;
p0->y = _gminor(p0->x, l);
}else if(c0 & 2){ /* push towards right edge */
p0->x = r.max.x-1;
p0->y = _gminor(p0->x, l);
}else if(c0 & 4){ /* push towards top edge */
p0->y = r.min.y;
if(l->slopeneg)
p0->x = _gmajor(p0->y-1, l)-1;
else
p0->x = _gmajor(p0->y, l);
}else if(c0 & 8){ /* push towards bottom edge */
p0->y = r.max.y-1;
if(l->slopeneg)
p0->x = _gmajor(p0->y, l);
else
p0->x = _gmajor(p0->y+1, l)-1;
}
c0 = code(p0, &r);
}
Return:
if(l->xmajor == 0){
XYswap(p0);
XYswap(p1);
}
if(swapped){
temp = *p0;
*p0 = *p1;
*p1 = temp;
}
return ret;
}
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