diff options
| -rw-r--r-- | isometric.c | 1 | ||||
| -rw-r--r-- | mkfile | 1 | ||||
| -rw-r--r-- | ptinline.c | 101 |
3 files changed, 103 insertions, 0 deletions
diff --git a/isometric.c b/isometric.c index afbe868..8e69ede 100644 --- a/isometric.c +++ b/isometric.c @@ -128,6 +128,7 @@ void drawtile(Tile *t, Point2 cell) { Point p; + cell.x *= TW; cell.y *= TH; p = toscreen(cell); @@ -7,6 +7,7 @@ TARG=\ bsplines\ grid\ isometric\ + ptinline\ HFILES=\ libgeometry/geometry.h\ diff --git a/ptinline.c b/ptinline.c new file mode 100644 index 0000000..97be46e --- /dev/null +++ b/ptinline.c @@ -0,0 +1,101 @@ +#include <u.h> +#include <libc.h> +#include <draw.h> + +int +max(int a, int b) +{ + return a > b? a: b; +} + +/* + * A Fast 2D Point-On-Line Test + * by Alan Paeth + * from "Graphics Gems", Academic Press, 1990 +*/ +int +ptinline(Point p, Point q, Point t) +{ + /* + * given a line through q and t + * return 0 if p is not on the line through <--q--t--> + * 1 if p is on the open ray ending at q: <--q + * 2 if p is on the closed interior along: q--t + * 3 if p is on the open ray beginning at t: t--> + */ + if(q.x == t.x && q.y == t.y){ + if(p.x == q.x && p.y == q.y) + return 2; + return 0; + } + + if(abs((t.y - q.y)*(p.x - q.x) - (p.y - q.y)*(t.x - q.x)) >= + max(abs(t.x - q.x), abs(t.y - q.y))) + return 0; + if((t.x < q.x && q.x < p.x) || (t.y < q.y && q.y < p.y)) + return 1; + if((p.x < q.x && q.x < t.x) || (p.y < q.y && q.y < t.y)) + return 1; + if((q.x < t.x && t.x < p.x) || (q.y < t.y && t.y < p.y)) + return 3; + if((p.x<t.x && t.x<q.x) || (p.y<t.y && t.y<q.y)) + return 3; + return 2; +} + +void +usage(void) +{ + fprint(2, "usage: %s\n", argv0); + exits("usage"); +} + +void +main(int argc, char *argv[]) +{ + Point pts[3]; + char buf[256], *p; + int n; + + fmtinstall('P', Pfmt); + ARGBEGIN{ + default: usage(); + }ARGEND; + if(argc > 0) + usage(); + + pts[0] = Pt(0,0); + pts[1] = Pt(2,2); + + while((n = read(0, buf, sizeof(buf)-1)) > 0){ + buf[n-1] = buf[n] = 0; + + pts[2].x = strtol(buf, &p, 10); + if(p == nil || *p == 0){ + fprint(2, "wrong x coordinate\n"); + continue; + } + pts[2].y = strtol(p, &p, 10); + if(p == nil || *p != 0){ + fprint(2, "wrong y coordinate\n"); + continue; + } + + switch(ptinline(pts[2], pts[0], pts[1])){ + case 0: + print("%P is not on %P%P\n", pts[2], pts[0], pts[1]); + break; + case 1: + print("%P in (∞,%P)\n", pts[2], pts[0]); + break; + case 2: + print("%P in [%P,%P]\n", pts[2], pts[0], pts[1]); + break; + case 3: + print("%P in (%P,∞)\n", pts[2], pts[1]); + break; + } + } + + exits(nil); +} |