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