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#ifndef lint |
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static const char RCSid[] = "$Id$"; |
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#endif |
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#ifndef lint |
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static char sccsid[] = "@(#)arc.c 4.1 (Berkeley) 6/27/83"; |
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#endif |
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|
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int del = 20; |
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step(d){ |
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del = d; |
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} |
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arc(x,y,x0,y0,x1,y1){ |
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double pc; |
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double sqrt(); |
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int flg,m,xc,yc,xs,ys,qs,qf; |
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float dx,dy,r; |
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char use; |
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dx = x-x0; |
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dy = y-y0; |
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r = dx*dx+dy*dy; |
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pc = r; |
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pc = sqrt(pc); |
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flg = pc/4; |
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if(flg == 0)step(1); |
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else if(flg < del)step(flg); |
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xc = xs = x0; |
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yc = ys = y0; |
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move(xs,ys); |
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if(x0 == x1 && y0 == y1)flg=0; |
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else flg=1; |
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qs = quad(x,y,x0,y0); |
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qf = quad(x,y,x1,y1); |
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if(abs(x-x1) < abs(y-y1)){ |
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use = 'x'; |
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if(qs == 2 || qs ==3)m = -1; |
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else m=1; |
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} |
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else { |
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use = 'y'; |
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if(qs > 2)m= -1; |
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else m= 1; |
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} |
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while(1){ |
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switch(use){ |
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case 'x': |
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if(qs == 2 || qs == 3)yc -= del; |
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else yc += del; |
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dy = yc-y; |
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pc = r-dy*dy; |
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xc = m*sqrt(pc)+x; |
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if((x < xs && x >= xc) || ( x > xs && x <= xc) || |
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(y < ys && y >= yc) || ( y > ys && y <= yc) ) |
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{ |
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if(++qs > 4)qs=1; |
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if(qs == 2 || qs == 3)m= -1; |
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else m=1; |
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flg=1; |
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} |
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cont(xc,yc); |
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xs = xc; |
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ys = yc; |
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if(qs == qf && flg == 1) |
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switch(qf){ |
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case 3: |
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case 4: |
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if(xs >= x1)return; |
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continue; |
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case 1: |
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case 2: |
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if(xs <= x1)return; |
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} |
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continue; |
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case 'y': |
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if(qs > 2)xc += del; |
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else xc -= del; |
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dx = xc-x; |
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pc = r-dx*dx; |
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yc = m*sqrt(pc)+y; |
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if((x < xs && x >= xc) || ( x > xs && x <= xc ) || |
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(y < ys && y >= yc) || (y > ys && y <= yc) ) |
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{ |
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if(++qs > 4)qs=1; |
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if(qs > 2)m = -1; |
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else m = 1; |
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flg=1; |
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} |
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cont(xc,yc); |
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xs = xc; |
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ys = yc; |
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if(qs == qf && flg == 1) |
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switch(qs){ |
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case 1: |
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case 4: |
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if(ys >= y1)return; |
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continue; |
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case 2: |
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case 3: |
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if(ys <= y1)return; |
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} |
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} |
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} |
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} |
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quad(x,y,xp,yp){ |
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if(x < xp) |
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if(y <= yp)return(1); |
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else return(4); |
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else if(x > xp) |
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if(y < yp)return(2); |
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else return(3); |
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else if(y < yp)return(2); |
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else return(4); |
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} |
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abs(a){ |
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if(a < 0)return(-a); |
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return(a); |
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} |
