void GraphicWindow::ellipse(double center_x, double center_y, double ra, double rb)
{
int cx = user_to_disp_x(center_x);
int cy = user_to_disp_y(center_y);
double a = fabs(user_to_disp_dx(ra));
double b = fabs(user_to_disp_dy(rb));
int x = 0;
int y = (int)(b + 0.5);
double d1 = b * b - a * a * b + a * a / 4;
set4(x, y, cx, cy);
while (a * a * (y - 0.5) > b * b * (x + 1))
{
if (d1 < 0)
{
d1 += b * b * (2 * x + 3);
x++;
}
else
{
d1 += b * b * (2 * x + 3) + a * a * (-2 * y + 2);
x++;
y--;
}
set4(x, y, cx, cy);
}
double d2 = b * b * (x + 0.5) * (x + 0.5) + a * a * (y - 1) * (y - 1) - a * a * b * b;
while (y > 0)
{
if (d2 < 0)
{
d2 += b * b * (2 * x + 2) + a * a * (-2 * y + 3);
x++;
y--;
}
else
{
d2 += a * a * (-2 * y + 3);
y--;
}
set4(x, y, cx, cy);
}
dirty = true;
}
void GraphicWindow::ellipse(double x, double y, double ra, double rb)
{
int disp_x = user_to_disp_x(x);
int disp_y = user_to_disp_y(y);
int disp_rx = abs(user_to_disp_dx(ra));
int disp_ry = abs(user_to_disp_dy(rb));
XSetForeground(display, xgc, BlackPixel(display, screen_num));
XDrawArc(display, win,
xgc, // the drawable
disp_x - disp_rx, // the x coord of upperleft corner of bounding rect
disp_y - disp_ry, // the y coord of upperleft corner of bounding rect
disp_rx * 2, // the major axis length
disp_ry * 2, // the minor axis length
0, // offset from 3 o'clock
360 * 64); // complete circle (360 degrees * 64 clicks per degree)
XDrawArc(display, _ppm, xgc, disp_x - disp_rx,
disp_y - disp_ry, disp_rx * 2, disp_ry * 2, 0, 360 * 64);
}
