How to draw a box in Unity Runtime?

Question

I'm currently working on an AR application that is able to measure volume. The functionality is required to draw a box is in the gif attached to this. I have tried to generate instantiating 3 points in a horizontal plane and then calculate the 4th point by vector calculations by this function.

Vector3 GetFourthPointPosition(Vector3 p1Transform, Vector3 p2Transform, Vector3 p3Transform)
{
    var OA = p1Transform;
    var OB = p2Transform;
    var OC = p3Transform;
    var OD = OC + OA - OB;
    GetFourthPoint(OA, OB, OC, OD);
    return OD;
}

Then, after that, I'm enabling a vertical plane and disable the horizontal plane to avoid adding points on the same axis. The last point is to calculate the height. After that, I'm instantiating 3 other points to generate the point view.

private void GetCompleteCube(Vector3 p1Transformation, Vector3 p2Transformation, Vector3 p3Transformation, Vector3 p4Transformation)
    {
        var height = Vector3.Distance(p3Transformation, p4Transformation);
        var length = Vector3.Distance(p1Transformation, p2Transformation);
        var width = Vector3.Distance(p2Transformation, p3Transformation);
        var invPointTransform = clone.transform.position;


        var p5Transformation = new Vector3(p1Transformation.x, p1Transformation.y + height, p1Transformation.z);
        var p6Transformation = new Vector3(p2Transformation.x, p1Transformation.y + height, p1Transformation.z);
        var p8Transformation = new Vector3(invPointTransform.x, invPointTransform.y + height, invPointTransform.z);


        InstantiatePoints(p1Transformation, p1Transformation, p3Transformation, p4Transformation, p5Transformation, p6Transformation, invPointTransform, p8Transformation);
    }

private void DrawCubeLineRendere(Vector3 p1Transformation, Vector3 p2Transformation, Vector3 p3Transformation, Vector3 p4Transformation, Vector3 p5Transformation, Vector3 p6Transformation, Vector3 p7Transformation, Vector3 p8Transformation)
{
        Vector3[] vertexPositions = new Vector3[] { p1Transformation, p2Transformation, p3Transformation, p7Transformation, p4Transformation, p5Transformation, p6Transformation, p8Transformation };
        lineRenderer.positionCount = vertexPositions.Length;
        lineRenderer.SetPositions(vertexPositions);
}

I'm tried using a line renderer t0 visualize the cube but the outcome is very odd. Does not lining to form a cuboid. it looks like this.

Can anybody help me to figure out what I have done wrong?

Answer 1

Instead of using a single line renderer, this uses 4 (you can go back for to 1 if you feel like it). Input are the first three points and the height (which you can as well later calculate/ generate on the fly).

The forth point is generated by simply subtracting the provided first three points.

Next we are generating with the cross product a normal vector and just use the corner pieces + the new normal vector + height to generate the other 4 points.

private void SetLineRenderer(LineRenderer lineRenderer, Vector3 p1, Vector3 p2, Vector3 p3, Vector3 p4) {
        Vector3[] vertexPositions = { p1, p2, p3, p4};
        lineRenderer.positionCount = 4;
        lineRenderer.loop = true;
        lineRenderer.SetPositions(vertexPositions);
    }

public void DrawCube(Transform p1, Transform p2, Transform p3, float height) {
        p4.position = p3.position + p1.position - p2.position;
        Vector3 crossProduct = Vector3.Cross(p2.position - p1.position, p4.position - p1.position).normalized * height;
        p5.position = p1.position - crossProduct;
        p6.position = p2.position - crossProduct;
        p7.position = p3.position - crossProduct;
        p8.position = p4.position - crossProduct;
        SetLineRenderer(l1, p1.position, p2.position, p3.position, p4.position);
        SetLineRenderer(l2, p5.position, p6.position, p7.position, p8.position);
        SetLineRenderer(l3, p1.position, p4.position, p8.position, p5.position);
        SetLineRenderer(l4, p2.position, p3.position, p7.position, p6.position);
    }

The circles are just for visual debugging if the math is right. If you want to draw in a single line renderer, you could pass the points p1, p2, p6, p2, p3, p7, p3, p4, p8, p4, p1, p5, p6, p7, p8. Loop does not need to be true but would not make a difference.