Creating a mesh "outline" around gameobject messes up when the gameobject rotates...

I have a gameobject, basically the character the player controls.

I want to create a mesh, that represents a “frame” of a trapezoid around this gameobject.

Creating the outer vertices works fine, but creating the inner vertices messes up (they are not evenly spaced away from the other vertices and the triangles I create seem to “flip” around and face the wrong direction and become invisible.

I have tried subtracting coordinates (but when the object rotates, these coordinates no longer are correct and the mesh looks messed up.

I have also tried scaling the outer vertices by a factor of 0.75, and this also seems to mess up too when the object is rotated.

How can I create this shape, without the rotation of the object throwing off the mesh creation?


This is pseudo code unfortunately, however I feel like the Vector3.Slerp method should be useful here possibly:

Vector3 OUL;
Vector3 OLL;
Vector3 OUR;
Vector3 OLR;

Float distIn = 0.5f; //how far in we come from the edge

//go round clockwise
Vector3 topEdge = (OUR-OUL).normalized*distIn;
Vector3 rightEdge = (OLR-OUR).normalized*distIn;
Vector3 bottomEdge = (OLL-OLR).normalized*distIn;
Vector3 leftEdge = (OUL-OLL).normalized*distIn;

Vector3 IUL = OUL + Vector3.Slerp(topEdge, -leftEdge, 0.5f);
Vector3 IUR = OUR + Vector3.Slerp(-topEdge, rightEdge, 0.5f);
Vector3 ILL = OLL + Vector3.Slerp(-bottomEdge, leftEdge, 0.5f);
Vector3 ILR = OLR + Vector3.Slerp(bottomEdge, -rightEdge, 0.5f);

Vector3[] verts = {OUL, OLL, OUR, OLR, IUL, IUR, ILL, ILR};

Int[] triangles = {	0, 2, 4,
			4, 2, 5,
			2, 3, 5,
			5, 3, 7,
			3, 1, 7,
			7, 1, 6,
			1, 0, 6,
			6, 0, 4};

Maybe you can make use of that, it should do the rotation calculations for you if you do it all within the same coordinates, i.e. either all world coords, or all local coords.

The problem in my opinion is, that you offset the inside along the x and y axis of the world, not of the gameObject. Try ofsetting them by transform.up * W + transform.right * W or something.

As far as looking at it from the bottom, it is transparent because Meshes are only rendered on one side. You should add all vertecies and triangles again with inverted order, so the triangles are set the other way around.

I found a “reasonable” solution, where I use the opposite sides, create a direction vector, and multiple by my intended “width” of the frame I want. It is slightly to big width-wise, but it should work for now. My complication was trying to create a function that creates the inner vertices FROM the outer ones, without using coordinates.

public static Vector3 TranslateDistanceBetweenPoints(this Vector3 start, Vector3 end, float distance) 
		Vector3 dir = end - start;
		Vector3 finalPos = start + (dir.normalized * distance);
		return finalPos;

public void generateMesh()
                //this assumes the "result" structure contains the outer vertices

                innerResult.UpperLeft = result.UpperLeft.TranslateDistanceBetweenPoints(result.LowerRight,widthOfFrame);
		innerResult.UpperRight = result.UpperRight.TranslateDistanceBetweenPoints(result.LowerLeft,widthOfFrame);
		innerResult.LowerLeft = result.LowerLeft.TranslateDistanceBetweenPoints(result.UpperRight,widthOfFrame);
		innerResult.LowerRight = result.LowerRight.TranslateDistanceBetweenPoints(result.UpperLeft,widthOfFrame);
		//now use these points to create a mesh from the inner and outer points
		Vector3[] vertices = new Vector3[]
		Vector3[] normals = 
		Vector2[] uv = new Vector2[]
			new Vector2(1, 1),
			new Vector2(1, 0),
			new Vector2(0, 1),
			new Vector2(0, 0),
			new Vector2(1, 1),
			new Vector2(1, 0),
			new Vector2(0, 1),
			new Vector2(0, 0)
		int[] triangles = new int[]
			0, 1, 4,
			4, 1, 5,
			2, 6, 7,
			2, 7, 3,
			2, 0, 4,
			2, 4, 6,
			7, 5, 1,
			7, 1, 3
		meshFilter.mesh.vertices = vertices;
		meshFilter.mesh.triangles = triangles;
		meshFilter.mesh.normals = normals;
		meshFilter.mesh.uv = uv;