CODEWITHSUNDEEP
openglopengl-es
nimish
nimish

Reputation: 4992

Use triangle normals in OpenGL to get vertex normals

I have a list of vertices and their arrangement into triangles as well as the per-triangle normalized normal vectors.

Ideally, I'd like to do as little work as possible in somehow converting the (triangle,normal) pairs into (vertex,vertex_normal) pairs that I can stick into my VAO. Is there a way for OpenGL to deal with the face normals directly? Or do I have to keep track of each face a given vertex is involved in (which more or less happens already when I calculate the index buffers) and then manually calculate the averaged normal at the vertex?

Also, is there a way to skip per-vertex normal calculation altogether and just find a way to inform the fragment shader of the face-normal directly?

Edit: I'm using something that should be portable to ES devices so the fixed-function stuff is unusable

Upvotes: 2

Views: 1667

Answers (1)

Tommy
Tommy

Reputation: 100632

I can't necessarily speak as to the latest full-fat OpenGL specifications but certainly in ES you're going to have to do the work yourself.

Although the normal was modal under the old fixed pipeline like just about everything else, it was attached to each vertex. If you opted for the flat shading model then GL would use the colour at the first vertex on the face across the entire thing rather than interpolating it. There's no way to recreate that behaviour under ES.

Attributes are per vertex and uniforms are — at best — per batch. In ES there's no way to specify per-triangle properties and there's no stage of the rendering pipeline where you have an overview of the geometry when you could distribute them to each vertex individually. Each vertex is processed separately, varyings are interpolation and then each fragment is processed separately.

Upvotes: 3

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