CODEWITHSUNDEEP
c#unity-game-engine
MidnightCoffee
MidnightCoffee

Reputation: 99

Unity Runtime Surface Snapping (Like Shift+Cntrl in Editor)

I am trying to allow the user of my VR game to move objects around using a pointer, then when holding down a button, snap to a grid and align to the highest surface, essentially replicating the Editor behavior or holding down shift+control and moving around a transform gizmo. (Try it, it's fun!)

I have the grid part down, but can't wrap my head around how to do the surface snapping. Here is the code I have so far. I would appreciate any and all help!

 
// offsetPos is where the VR pointer is.
Vector3 offsetPos = pointer.objectControlPoint.transform.position + cursorOffset;
Vector3 newPos;
 
if (isSnapping) // Snap to ground code.
{
// I read previously to do this up then down thing, but It's not working as expected
    RaycastHit groundHit = new RaycastHit();
    if (Physics.Raycast(selectedObject.transform.position, Vector3.down, out groundHit))
    {
         RaycastHit objectHit = new RaycastHit();
         if (Physics.Raycast(groundHit.point, Vector3.up, out objectHit))
         {
                Vector3 snapDiff = groundHit.point - objectHit.point;
                snapYPos = snapDiff.y + (selectedObject.collider.bounds.extents.y);
          }
    }
      // worldGrid is a monoBehavior on another object, and gridCellSize is just a float
      float gridPosX = Mathf.Floor(offsetPos.x / worldGrid.gridCellSize) * worldGrid.gridCellSize;
      float gridPosZ = Mathf.Floor(offsetPos.z / worldGrid.gridCellSize) * worldGrid.gridCellSize;
      newPos = new Vector3(gridPosX, snapYPos, gridPosZ); // Sets the target position to the nearest grid cell, with a Y of the snap position.
}
else // If not in snap mode, set target position to just the VR cursor.
{
       newPos = new Vector3(offsetPos.x, offsetPos.y, offsetPos.z);
}
 
// I know lerp might not be the most efficient, but I like the smooth effect, and it looks good when snapping to the grid...
selectedObject.transform.position = Vector3.Lerp(selectedObject.transform.position, newPos, movementLerpSpeed * Time.deltaTime);

The objects I need to be snapping all are different sizes and have their origins in different places, but all do have appropriate box colliders.

Thanks so much!

Upvotes: 0

Views: 2247

Answers (1)

derHugo
derHugo

Reputation: 90862

If I understand you correctly now and you actually just struggle at the correct value for Y I think you are actually almost there.

Except that currently you only get the delta between the two points on the Colliders. But you need to take into account also any offset between objects and their colliders. I'll try to illustrate it

 ---------
 |       |
 |  °    |
 |   x   |  -------
 |       |  |     |
 |       |  |  x  |
 ---------  | °   |
            -------

Let's say here x is the actual BoxCollider center and ° is the actual object transform.position.

So assuming the objects are not rotated at all I would not go through the bounds but rather do

if (Physics.Raycast(selectedObject.transform.position, Vector3.down, out var groundHit))
{
    var groundCollider = groundHit.gameObject.GetComponent<BoxCollider>();
    var groundTopY = groundHit.transform.TransformPoint(groundCollider.center + groundCollider.size * 0.5f).y;

    var selectedCollider = selectedObject.GetComponent<BoxCollider>();
    var selectedBottomY = selectedObject.transform.TransformPoint(selectedCollider.center - selectedCollider.size * 0.5f).y;
    var selectedCenterOffsetY = selectedObject.transform.TransformPoint(selectedCollider.center).y;

    snapYPos = groundTopY + (groundTopY - selectedBottomY) - selectedCenterOffsetY; 
}

Typed on smartphone but I hope the idea gets clear

Upvotes: 2

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