Why lighting appears on opposite side?

Question

I am trying to build lighting using this tutorial. However, lighting appears on wrong side of human object and I do not know why.

Normals were created per triangle. Vert

Answer 1

I think the cause of your problem is that you are not applying your model transformation to your normal vectors. Since you definitely do not want to skew them, you will have to create a special matrix for your normals.

As is explained further down the tutorial that you mentioned, the matrix can be constructed like this

Normal = mat3(transpose(inverse(model))) * aNormal;

in your vertex shader. However, I highly recommend that you calculate the matrix in your application code instead, since you would calculate it per vertex in the above example. Since you are using the glm library, it would look like this instead:

glm::mat3 model_normal = glm::mat3(glm::transpose(glm::inverse(model)));

You can then load your new model_normal matrix into the shader as a uniform mat3.