draw_arc

COPY/// draw_arc(x1,y1,x2,y2,x3,y3,x4,y4,precision)
//
//  Draws an arc of an ellipse mimicking draw_arc() from GM5. It also mimics
//  draw_ellipse() from GM6 in that it uses a primitive drawn with limited
//  resolution. The arc is drawn following the perimeter of the ellipse, 
//  counterclockwise, from the starting point to the ending point.
//  The starting point is the intersection of the ellipse with the ray 
//  extending from the center point and passing through the point (x3,y3).
//  The ending point is the intersection of the ellipse with the ray
//  extending from the center through the point (x4,y4).
//
//      x1,y1       1st corner of bounding rectangle, real
//      x2,y2       2nd corner of bounding rectangle, real
//      x3,y3       determines starting point, real
//      x4,y4       determines ending point, real
//      precision   number of segments a full ellipse would be drawn with,
//                  [4..64] divisible by 4, default 24, real (optional)
//
/// gmlscripts.pro/license
{
    var x1,y1,x2,y2,x3,y3,x4,y4,precision;
    x1 = argument0;
    y1 = argument1;
    x2 = argument2;
    y2 = argument3;
    x3 = argument4;
    y3 = argument5;
    x4 = argument6;
    y4 = argument7;
    precision = argument8;
    if (precision == 0) precision = 24;
    var res,xm,ym,xr,yr,r,a1,a2,sx,sy,a;
    res = 360 / min(max(4,4*(precision div 4)),64);
    xm = (x1+x2)/2;
    ym = (y1+y2)/2;
    xr = abs(x2-x1)/2;
    yr = abs(y2-y1)/2;
    if (xr > 0) r = yr/xr;
    else r = 0;
    a1 = point_direction(0,0,(x3-xm)*r,y3-ym);
    a2 = point_direction(0,0,(x4-xm)*r,y4-ym);
    if (a2<a1) a2 += 360;
    draw_primitive_begin(pr_linestrip);
    sx = xm+lengthdir_x(xr,a1);
    sy = ym+lengthdir_y(yr,a1);
    draw_vertex(sx,sy);
    for (a=res*(a1 div res + 1); a<a2; a+=res) {
        sx = xm+lengthdir_x(xr,a);
        sy = ym+lengthdir_y(yr,a);
        draw_vertex(sx,sy);
    }
    sx = xm+lengthdir_x(xr,a2);
    sy = ym+lengthdir_y(yr,a2);
    draw_vertex(sx,sy);
    draw_primitive_end();
    return 0;
}