Writing a paint program à la MS Paint - how to interpolate between mouse move events?

Question

I want to write a paint program in the style of MS Paint.

For painting things on screen when the user moves the mouse, I have to wait for mouse move events and draw

Answer 1

I agree with harviz - the problem isn't solved. It should be solved on the operating system level by recording mouse movements in a priority thread, but no operating system I know of does that. However, the app developer can also work around this operating system limitation by interpolating better than linear.

Since mouse movement events don't always come fast enough, linear interpolation isn't always enough.

I experimented a little bit with the spline idea brought up by Rocketmagnet.

Instead of putting a line between two points A and D, look at the point P preceding A and use a cubic spline with the following control points B = A + v' and C = D - w', where

v = A - P,
w = D - A,
w' = w / 4 and
v' = v * |w| / |v| / 4.

This means we fall into the second point with the same angle as the line interpolation would, but go out a starting point in the same angle the previous segment came in, making the edge smooth. We use the length of the segment for both control point distances to make the size of the bend fit its proportion.

The following picture shows the result with very few data points (indicated in grey).

The sequence starts at the top left and ends in the middle.

There is still some level of uneasiness here which may be alleviated if one uses both the previous and the next point to adjust for both angles, but that would also mean to draw one point less than what one has got. I find this result already satisfactory, so I didn't try.