Added readonly OffsetInBytes and ElementType variables to GenericVAO

[TheRealNOIG]

Ran into "System.TypeAccessException" error when creating costume VAO's

[giawa]

Same thing here, is this a good candidate for either a public or protected property instead of an exposed field?

[TheRealNOIG]

I don't remember what I was using this for but looking at the changes I think setting offset to private should be fine because there is already a exposed variable Offset. Than we can set offsetInBytes to readonly. As for allowIntAsElementType I don't remember but looking through the comments my guess is that the child class would need to read and write access. Let me know if these changes sound good to you.

[giawa]

It doesn't look like you ever edited allowIntAsElementType, at least not in the commits for this PR. Is that modification really needed? I think it might even be worth pulling all that code out in a future commit/PR since it really shouldn't be supported (even if it works in practice). offsetInBytes as read-only sounds fine to me.

[TheRealNOIG]

Ok I did a real fast search over one of my projects that I think was the reason this PR was made.

foreach (KeyValuePair<GenericVAO, List<ModelEntity>> item in entityDictionary)
{
    GenericVAO model = item.Key;
    PrepareModel(model);
    foreach (Entity entity in item.Value)
    {
        shader.LoadTransformationMatrix(Maths.CreateTransformationMatrix(entity));
        Gl.DrawElements(model.DrawMode, model.VertexCount, model.elementType, model.offsetInBytes);
    }
    UnBindModel();
}

Because of this, it looks like it should be fine to set offsetInBytes and elementType to readonly