Unity - X axis back to front

Question

I'm using Unity 2018 and its really confusing me. I generate a plane mesh in code and when it comes to positioning (transform.position.x) it on the X axis I can't understand why moving it further to the right the X value decreases (into the negatives) and the X value increases to the left??

The Y axis works as expected, up increases the value (positive), down decreases (negative). The Z axis, away from camera = negative and towards = positive.

(Just creating a basic 3D cube game object using the Unity Create tool, the same issue applies.)

I need to figure if this is how Unity is set up now? Or I'm doing something wrong.. But I'm stuck on this!!

//create mesh code:

Mesh CreateMesh(float width, float height)
    {
        Mesh m = new Mesh();
        m.name = "ScriptedMesh";
        m.vertices = new Vector3[] {
         new Vector3(0, 0, 0.01f),
         new Vector3(width, 0, 0.01f),
         new Vector3(width, height, 0.01f),
         new Vector3(0, height, 0.01f)
     };
        m.uv = new Vector2[] {
         new Vector2 (0, 0),
         new Vector2 (0, 1),
         new Vector2(1, 1),
         new Vector2 (1, 0)
     };
        m.triangles = new int[] { 0, 1, 2, 0, 2, 3 };
        m.RecalculateNormals();

        return m;
    }

//build our first wall mesh obj

                    var wallObj = new GameObject("Wall-" + wallc.WallLengthCM + " (" + wallIndex + ")");
                    var _wallMesh = (MeshFilter)wallObj.AddComponent(typeof(MeshFilter));
                    _wallMesh.mesh = CreateMesh((float)wallc.WallLengthCM, (float)wallc.WallHeightCM);
                    MeshRenderer wallRenderer = wallObj.AddComponent(typeof(MeshRenderer)) as MeshRenderer;
                    wallRenderer.material = ShedWallMat;
var wallMesh = Instantiate(_wallMesh,
                new Vector3 { x = 0, y = ((float)wallc.WallHeightCM * 2 * wallIndex) + vertSpace, z = 0 },
                new Quaternion { w = 0, x = 0, y = 0, z = 0 });

Answer 1

Unity's coordinate system is a little different than you described. From the perspective of the default camera in a new scene (looking along the z+ axis):

• X+ = right
• Y+ = up
• Z+ = forward / away from the default camera (not negative as described in the question)

In this example you've turned your viewpoint around to look "backward" along the world's negative Z axis, so naturally the positive X axis is turned to point leftward from this perspective.

If you turn your view around the other side, you'll find that your mesh disappears. That's because you've wound your triangles in counter-clockwise order, but Unity's materials treat clockwise triangles as front-facing by default. Simply interchange two indices of each triangle to match this convention.

One last minor issue: an all-zero quaternion does not correspond to a 3D rotation. We typically want our quaternions to be unit length. So you may want {w = 1, x = 0, y = 0, z = 0} instead, also available as the constant Quaternion.identity (I suspect Unity is falling back to this when given all zeroes anyway)