My Y normals (for directional lighting) seems backwards?

[trusktr]

When making directional lighting, I found that for normals of a face that faces upwards (which is in the positive Y direction right?) that my normal is 0, -1, 0, which seems to be backwards? I thought it would be +1 on the Y axis, since positive is up. For example, here's the normals for each side of my cube, (the cube sides are perpendicular to the XYZ axes), and it seems that "top" and "bottoms" face normals are backwards:

        const normals = [
            [0,0,1, ], // front face
            [-1,0,0, ], // left face
            [1,0,0,], // right face
            [0,0,-1,], // back face
            [0,-1,0, ], // top face
            [0,1,0,], // bottom face
        ]

Here's the full code.

Here's how the cubes are created, the sides are just perpenducular/parallel to axes.

As you can see, the top face is created 5th, and the top-face normal is also fifth in the above normals array, then the normals are mapped to the vertices.

I thought that the top face, which faces upwards, would have vertex normals of 0,1,0, and the bottom face would have vertex normals of 0,-1,0.

Why might it be opposite?

[trusktr]

The full working example can be seen here: https://trusktr.io (for now).

[trusktr]

@greggman oh oh!! Is it because the ordering of my vertices is clockwise (so the right hand rule would make the normal point downward)?

Does the normal direction become opposite if we reverse the ordering of the vertices?

[trusktr]

Ah, yep, I forgot that in the webgl-3d-orthographic lesson the order of the vertices determines front/back of the triangle, which determines direction of the normal.

[greggman]

No, the normal doesn't flip based on the clockwise or counterclockwise unless you are computing the normal. You're not computing the normal you're supplying it precomputed. As for your question you should ask this on Stack Overflow and if you want debugging help you should make a minimal example.

Here's a simple cube
https://jsfiddle.net/greggman/ksu95xjj/

The top face's normal is [0, 1, 0]. The bottom is [0, -1, 0] as you'd expect.