TEITTINEN@cc.helsinki.fi (09/05/89)
I need a fast algorithm to draw arcs. The given values are centerpoint (x,y) of the circle/ellipse, x- and y-radius, starting angle and ending angle. C function preferred, but any language or plain algorithm appreciated. Thanks in advance -- EARN: teittinen@finuh ! "Studying is the only way Internet: teittinen@cc.helsinki.fi ! to do nothing without Marko Teittinen, student of computer science ! anyone blaming you" -me
mccaugh@s.cs.uiuc.edu (09/10/89)
#include <math.h>
void DrawArc(a,b, x0,y0, theta1,theta2) /* draw arc from theta1 to theta2 */
float a,b, x0,y0, theta1,theta2; /* with all angles in radians */
/* a = x-radius, b = y-radius, (x0,y0) = center */
{
#define Degree 0.0174532
float a2,b2, ab, theta,tan_theta, x,y, Pi_2, Pi_3_2;
a2 = a*a; b2 = b*b; ab = a*b; Pi_2 = 0.5*Pi(); Pi_3_2 = 3.0*Pi_2;
for (theta=theta1; theta<=theta2; theta+=Degree) /* increment = 1 degree */
{
if(theta==Pi_2)
{
x = x0;
y = y0+b;
}
else if(theta==Pi_3_2)
{
x = x0;
y = y0-b;
}
else {
tan_theta = tan(theta);
x = x0 + ab/sqrt(b2 + a2*tan_theta*tan_theta);
y = y0 + (x-x0)*tan_theta;
}
PutPixel(round(x),round(y),color);
}
}
I sincerely hope this helps.
Scott McCaughrin
Dept. of Computer Science
University of Illinoismccaugh@s.cs.uiuc.edu (09/10/89)
Incidentally, if you have access to Turbo-C, I believe that it has a graphic primitive called 'ellipse' which takes these same parameters (see declaration in: graphics.h); it also has 'putpixel' with the same declaration as I have assumed. Furthermore, the function Pi() is supplied (in: math.h) by M_PI (to 18 places) and M_PI_2 replaces my Pi_2. But you would still need Pi_3_2. Scott McCaughrin