Handles.Slider

static function Slider (position : Vector3, direction : Vector3) : Vector3

static function Slider (position : Vector3, direction : Vector3, size : float, drawFunc : DrawCapFunction, snap : float) : Vector3

Parameters

Name	Description
position	the position of the current point.
direction	the direction of the sliding.
float	3D size the size of the handle - HandleUtility.GetHandleSize (position);
drawFunc	the function to call for doing the actual drawing - by default, it's Handles.ArrowCap, but any function that has the same signature can be used. Note: Use HandleUtility.GetHandleSize where you might want to have constant screen-sized handles.

Description

Make a 3D slider

This will draw a 3D-draggable handle on the screen. The handle is constrained to sliding along a direction vector in 3D space.

Slider handle in the Scene View.

// Simple script that creates a Magenta Slide Handle that 
// points to (0,0,0) nomatter where the target GameObject is located.

@CustomEditor (Slide)
class SliderHandleJS extends Editor {
    function OnSceneGUI () {
        Handles.color = Color.magenta;
        target.vectorPoint = Handles.Slider (target.transform.position, 
                              Vector3.zero - target.transform.position);
        if (GUI.changed)
            EditorUtility.SetDirty (target);
    }
}

And the script attached to this Handle:

// Usage: Place this script on the Game Object you want to use the
// editor-created slide handle.

@script ExecuteInEditMode()

var vectorPoint : Vector3 = Vector3(0,0,0);

function Update() {
    Debug.Log("Looking at: " + vectorPoint);
}