Physics Simulation - 3D Game Development Practical Introduction - page 280

Illustration 65: Line renderer that draws launch direction indicator
You can use any material you want to render the line. Here I use a custom material called
Line , which is simply a gradient of blue and orange. The number of positions we need is
2: a start point and an end point. The positions are by default zero, but we are going to
change them according to user input. The script PhysicsProjectile shown in Listing 54 must
be added to the ball object to turn it into a controllable projectile that can be launched using
mouse drag.