| src | The source point of the drag. |
| dest | The destination point of the drag. |
| srcPosition | The 3D position the dragged object had at src ray. |
| constraintDir | 3D direction of constrained movement. |
float The distance travelled along constraintDir.
Map a mouse drag onto a movement along a line in 3D space.
Certain types of Handles (such as arrows) involve movement along a line in 3D space. For example, the Transform's position arrows move the object along its local X, Y or Z axis as the mouse is dragged. The CalcLineTranslation function converts the movement of the mouse into constrained movement along a 3D line in the familiar way used by Unity's built-in tools.