Moving a character with touch controls relative to target?

16-02-2016

I have since reworked my controls to raycast on to the scene and the player moves towards that. This is still not my preferred method of movement, but I will be closing this question to link to a more descriptive question that explains better my intentions or needs. Thank you for the support. http://answers.unity3d.com/questions/1141246/how-can-i-get-vector-coordinates-from-a-raycast-re.html

~hy

Hello,
I am building a game where the camera is at a fixed position, rotation, etc. from a character. The camera is simply given a position offset from the character object. I have built controls to move this character based on the screen position of an input. This began to slowly fall apart as I have been unable to come up with a way to arbitrarily modify the origin of the movement.
I need a way to either:
-move the character relative to the centre of the screen
-move the character relative to its current position

At the moment it:
-moves relative to 0-1 scale screen coordinates (bottom-left is 0,0; top-right is 1,1)
-will only move left and downwards normally (the inverse of the screen's y-coordinate)

If a code sample is needed, here is the section of trouble (C#):

 public float walk = 12f;
     void Update(){
         if( (INPUT CONDITIONS) ){
             #if (UNITY_EDITOR || UNITY_STANDALONE)
             mdown = Camera.main.ScreenPointToRay(Input.mousePosition);
             #elif (UNITY_ANDROID || UNITY_IPHONE)
             mdown = Camera.main.ScreenPointToRay(Input.GetTouch(0).position);
             #endif
             RaycastHit mpointhit;
             
             if(Physics.Raycast(mdown, out mpointhit)){
                 mpoint.x = mpointhit.point.x;
                 mpoint.z = mpointhit.point.z;
                 move = new Vector3(mpoint.x, 0, mpoint.z);
                 move *= walk;
             }
         }
         user.transform.position += move*Time.deltaTime;
 }

I have taken out sections of comments and attempts to "reposition" the origin of movement, which included using Camera.main.pixelRect.center.
Thank you