Smooth Tangent Space Normals for Enhanced Bump Mapping

In an attempt to enhance the visual quality of 3D models, many graphics applications employ bump mapping techniques. However, achieving smooth and realistic results can pose challenges when tangent space normals are calculated solely based on face data.

Calculation Details

The current approach calculates tangent, binormal, and normal vectors on a per-face basis, neglecting the normals already present in the model file. This technique utilizes edge data and texture space vectors to determine these values, relying on a cross product to ultimately derive the normal.

Facet Problem

This approach often results in a faceted appearance, with sharp edges and unnatural transitions between faces. This occurs because the calculated normals are not continuous across vertices, causing abrupt changes in lighting and shading.

Solution: Vertex-Based Normals

To address this issue, the solution lies in calculating normals on a per-vertex basis. This can be achieved by utilizing the normals provided in the model file or smoothing them out to prevent faceting.

Algorithm

1. Initialize Vertex Normal Accumulators: Assign each vertex an initial normal vector of (0, 0, 0).
2. Calculate and Accumulate Face Normals: For each face, compute its normal vector as usual. Add this normal to the normal accumulators of the vertices used in that face.
3. Normalize Accumulated Normals: Divide each vertex's normal accumulator by the count of faces it belongs to. This results in an average normal.
4. Tangent and Binormal Calculation: Utilize the average vertex normals, along with edge data and texture space vectors, to calculate the tangent and binormal vectors per vertex.
5. Use Smooth Normals: The resulting vertex normals provide a smoother base for tangent space calculations, eliminating the faceted appearance and enhancing the realism of the bump mapping.