Circle
A point on a circle can be defined by its x,y coordinates. Given the radius of the circle r and the x coordinate, use the following formula to calculate the point's y coordinate.
r2 = x2 + y2
y = sqrt(r2 - x2)
Now that you have the x,y coordinate of a point on a circle, reduce y using the tilt angle. (This assumes the viewer is at +Z infinity with no perspective.)
Given circle radius r and tilt angle θ ...
y = sqrt(cos2(θ) * (r2 - x2))
y = round(sqrt(cos2(θ) * (r2 - x2)))
Do this for any x coordinate you want to plot.
Note: sqrt is the square root function. It returns a float. For pixel coordinates round y to an integer.
FYI
| cos(0°) | 0.000 |
| cos(30°) | 0.866 |
| cos(45°) | 0.707 |
| cos(60°) | 0.500 |
| cos(90°) | 1.000 |