Moving Unit Parallel to Mouse in TBS Game

Question

I'm writing a basic Turn-Based Strategy game using Unity3D. It's not grid-based. I've come to the point where I'm coding unit movement, and I'm having trouble figuring out how far to move the units based on the mouse position. The following image is what I want:

The unit should snap forward along the red vector; it will always move in the direction it's facing. The reason I'm doing it this way is because I want the user to be able to see the result of their move, and I want to avoid some sort of GUI slider. The blue vector represents the vector from the mouse to the target point.

So, to sum it up: how do I calculate the movement (red) vector, based on the unit and mouse positions? Pseudo-code would be great!

Answer 1

It's not entirely clear, but I understand the unit will only be able to move in the direction it is facing. In that case you will need to factor that vector into the equation as well (next to the unit and mouse positions).

Have a look at the equations in Minimum Distance between a Point and a Line by Paul Bourke.

In this picture, your unit's position is P1, P2 can be found by adding its facing vector to its position, and P3 is the position of the mouse cursor. The point of intersection gives you the endpoint for the movement.