projects / unix-history / blame
| Commit | Line | Data |
|---|---|---|
| c899e3cf RC |
1 | #ifndef lint |
| 2 | static char sccsid[] = "@(#)arc.c 4.1 (Berkeley) %G%"; | |
| 3 | #endif | |
| 4 | ||
| 5 | #include "hp7221.h" | |
| 6 | ||
| 7 | /* | |
| 8 | * 7221 requires knowing the anlge of arc. To do this, the triangle formula | |
| 9 | * c^2 = a^2 + b^2 - 2*a*b*cos(angle) | |
| 10 | * is used where "a" and "b" are the radius of the circle and "c" is the | |
| 11 | * distance between the beginning point and the end point. | |
| 12 | * | |
| 13 | * This gives us "angle" or angle - 180. To find out which, draw a line from | |
| 14 | * beg to center. This splits the plane in half. All points on one side of the | |
| 15 | * plane will have the same sign when plugged into the equation for the line. | |
| 16 | * Pick a point on the "right side" of the line (see program below). If "end" | |
| 17 | * has the same sign as this point does, then they are both on the same side | |
| 18 | * of the line and so angle is < 180. Otherwise, angle > 180. | |
| 19 | */ | |
| 20 | ||
| 21 | #define side(x,y) (a*(x)+b*(y)+c > 0.0 ? 1 : -1) | |
| 22 | ||
| 23 | arc(xcent,ycent,xbeg,ybeg,xend,yend) | |
| 24 | int xcent,ycent,xbeg,ybeg,xend,yend; | |
| 25 | { | |
| 26 | double radius2, c2; | |
| 27 | double a,b,c; | |
| 28 | int angle; | |
| 29 | ||
| 30 | /* Probably should check that this is really a circular arc. */ | |
| 31 | radius2 = (xcent-xbeg)*(xcent-xbeg) + (ycent-ybeg)*(ycent-ybeg); | |
| 32 | c2 = (xend-xbeg)*(xend-xbeg) + (yend-ybeg)*(yend-ybeg); | |
| 33 | angle = (int) ( 180.0/PI * acos(1.0 - c2/(2.0*radius2)) + 0.5 ); | |
| 34 | ||
| 35 | a = (double) (ycent - ybeg); | |
| 36 | b = (double) (xcent - xbeg); | |
| 37 | c = (double) (ycent*xbeg - xcent*ybeg); | |
| 38 | if (side(xbeg + (ycent-ybeg), ybeg - (xcent-xbeg)) != side(xend,yend)) | |
| 39 | angle += 180; | |
| 40 | ||
| 41 | move(xcent, ycent); | |
| 42 | /* Not quite implemented... | |
| 43 | printf("C(A%d c)[%d,%d]", angle, xbeg, ybeg); | |
| 44 | */ | |
| 45 | } |