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Annotation of researchv9/jerq/src/lib/mj/arc.c, revision 1.1.1.1

1.1       root        1: #ifndef        MUX
                      2: #define        Jcursinhibit()  cursinhibit()
                      3: #define        Jcursallow()    cursallow()
                      4: #define        lrectf(l, r, f) rectf(l, r, f)
                      5: #define        lpoint(l, p, f) point(l, p, f)
                      6: #endif
                      7: 
                      8: #include <jerq.h>
                      9: static Point nearby();
                     10: #define sq(x) ((long)(x)*(x))
                     11: #define        sgn(x)  ((x)<0? -1 : (x)==0? 0 : 1)
                     12: #define labs(x)        (x<0? -x : x)
                     13: #define        DB              ((Word *)0x700000)
                     14: #define        ONSCREEN(b)     (b->base>=DB && b->base<DB+XMAX/WORDSIZE*YMAX)
                     15: 
                     16: /*     Draw an approximate arc centered at x0,y0 of an
                     17:  *     integer grid and running anti-clockwise from
                     18:  *     x1,y1 to the vicinity of x2,y2.
                     19:  *     If the endpoints coincide, draw a complete circle.
                     20:  *
                     21:  *     The "arc" is a sequence of vertically, horizontally,
                     22:  *     or diagonally adjacent points that minimize 
                     23:  *     abs(x^2+y^2-r^2).
                     24:  *
                     25:  *     The circle is guaranteed to be symmetric about
                     26:  *     the horizontal, vertical, and diagonal axes
                     27:  */
                     28: arc(bp, p0, p2, p1, f)
                     29:        register Bitmap *bp;
                     30:        Point p0, p1, p2;
                     31: {
                     32:        short inhibited;
                     33:        register dx, dy;
                     34:        register eps;   /* x^2 + y^2 - r^2 */
                     35:        int dxsq, dysq; /* (x+dx)^2-x^2, ...*/
                     36:        int ex, ey, exy;
                     37:        p1=sub(p1, p0);
                     38:        p2=sub(p2, p0);
                     39:        p2=nearby(p1, p2);
                     40:        dx = -sgn(p1.y);        /* y1==0 is soon fixed */
                     41:        dy = sgn(p1.x);
                     42:        dxsq = (2*p1.x + dx)*dx;
                     43:        dysq = (2*p1.y + dy)*dy;
                     44:        eps = 0;
                     45:        inhibited=0;
                     46:        if(f!=F_XOR && ONSCREEN(bp)){
                     47:                Jcursinhibit();
                     48:                inhibited=1;
                     49:        }
                     50:        do {
                     51:                if(p1.x == 0) {
                     52:                        dy = -sgn(p1.y);
                     53:                        dysq = (2*p1.y + dy)*dy;
                     54:                } else if(p1.y == 0) {
                     55:                        dx = -sgn(p1.x);
                     56:                        dxsq = (2*p1.x + dx)*dx;
                     57:                }
                     58:                ex = abs(eps + dxsq);
                     59:                ey = abs(eps + dysq);
                     60:                exy = abs(eps + dxsq + dysq);
                     61:                if(ex<ey || exy<=ey) {
                     62:                        p1.x += dx;
                     63:                        eps += dxsq;
                     64:                        dxsq += 2;
                     65:                }
                     66:                if(ey<ex || exy<=ex) {
                     67:                        p1.y += dy;
                     68:                        eps += dysq;
                     69:                        dysq += 2;
                     70:                }
                     71:                lpoint(bp, Pt(p0.x+p1.x, p0.y+p1.y), f);
                     72:        } while(!(p1.x==p2.x && p1.y==p2.y));   /* Note1 */
                     73:        if(inhibited)
                     74:                Jcursallow();
                     75: }
                     76: /*     Note1: the equality end test is justified
                     77:  *     because it is impossible that
                     78:  *     abs(x^2+y^2-r^2)==abs((x++-1)^2+y^2-r^2) or
                     79:  *     abs(x^2+y^2-r^2)==abs(x^2+(y++-1)-r^2),
                     80:  *     and no values of x or y are skipped.
                     81:  *
                     82:  */
                     83: static Point nearby(p1, p2)
                     84:        Point p1, p2;
                     85: {
                     86:        long eps, exy;  /*integers but many bits*/
                     87:        int d;
                     88:        register dy;
                     89:        register dx;
                     90:        register x1 = p1.x;
                     91:        register y1 = p1.y;
                     92:        register x2 = p2.x;
                     93:        register y2 = p2.y;
                     94:        eps = sq(x2) + sq(y2) - sq(x1) - sq(y1);
                     95:        d = eps>0? -1: 1;
                     96:        for( ; ; eps=exy, x2+=dx, y2+=dy) {
                     97:                if(abs(y2) > abs(x2)) {
                     98:                        dy = d*sgn(y2);
                     99:                        dx = 0;
                    100:                } else {
                    101:                        dy = 0;
                    102:                        dx = d*sgn(x2);
                    103:                        if(dx==0)
                    104:                                dx = 1;
                    105:                }
                    106:                exy = eps + (2*x2+dx)*dx + (2*y2+dy)*dy;
                    107:                if(labs(eps) <= labs(exy))
                    108:                        break;
                    109:        }
                    110:        p2.x = x2;
                    111:        p2.y = y2;
                    112:        return(p2);
                    113: }

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