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Annotation of researchv9/jerq/src/lib/j/circle.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: #define        DB              ((Word *)0x700000)
                     10: #define        ONSCREEN(b)     (b->base>=DB && b->base<DB+XMAX/WORDSIZE*YMAX)
                     11: /*     Form a circle of radius r centered at x1,y1
                     12:  *     The boundary is a sequence of vertically, horizontally,
                     13:  *     or diagonally adjacent points that minimize 
                     14:  *     abs(x^2+y^2-r^2).
                     15:  *
                     16:  *     The circle is guaranteed to be symmetric about
                     17:  *     the horizontal, vertical, and diagonal axes
                     18:  */
                     19: circle(b,p,r,f)
                     20:        Bitmap *b;
                     21:        Point p;
                     22: {
                     23:        short inhibited;
                     24:        int x1=p.x;
                     25:        register y1=p.y;
                     26:        register eps = 0;       /* x^2 + y^2 - r^2 */
                     27:        register dxsq = 1;              /* (x+dx)^2-x^2*/
                     28:        register dysq = 1 - 2*r;
                     29:        register exy;
                     30:        int x0 = x1;
                     31:        register y0 = y1 - r;
                     32:        y1 += r;
                     33:        if (f == F_XOR) {       /* endpoints coincide */
                     34:                point(b,Pt(x0,y0),f);
                     35:                point(b,Pt(x0,y1),f);
                     36:                inhibited=0;
                     37:        }else if(ONSCREEN(b)){
                     38:                Jcursinhibit();
                     39:                inhibited=1;
                     40:        }
                     41:        while(y1 > y0) {
                     42:                lpoint(b,Pt(x0,y0),f);
                     43:                lpoint(b,Pt(x0,y1),f);
                     44:                lpoint(b,Pt(x1,y0),f);
                     45:                lpoint(b,Pt(x1,y1),f);
                     46:                exy = eps + dxsq + dysq;
                     47:                if(-exy <= eps+dxsq) {
                     48:                        y1--;
                     49:                        y0++;
                     50:                        eps += dysq;
                     51:                        dysq += 2;
                     52:                }
                     53:                if(exy <= -eps) {
                     54:                        x1++;
                     55:                        x0--;
                     56:                        eps += dxsq;
                     57:                        dxsq += 2;
                     58:                }
                     59:        }
                     60:        lpoint(b,Pt(x0,y0),f);
                     61:        lpoint(b,Pt(x1,y0),f);
                     62:        if(inhibited)
                     63:                Jcursallow();
                     64: }

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