How Can I Efficiently Handle Separate Vertex and Normal Indices in OpenGL for Custom Mesh Formats?

Overcoming Index Buffer Difficulties in OpenGL

When dealing with custom file formats for 3D meshes, managing different indices for vertices and normals can present challenges in OpenGL. However, there is a straightforward solution to this issue.

OpenGL requires a single index buffer for both vertices and normals. To address this, it is necessary to create an OpenGL vertex for each unique pair of vertex index and normal index in the input file.

To do this, utilize a data structure like a STL map, where the key is the (vertex index, normal index) pair. Iterate over the input mesh data, adding each unique pair as a key to the map and assigning a corresponding index value. In this way, the map acts as a lookup table for combining vertex and normal data.

Create new arrays or vectors for the combined vertices and indices. As the input triangles are processed, use the lookup table to determine the corresponding combined index for each corner. Add this index to the combinedIndices vector. Additionally, extract the corresponding vertex and normal coordinates from the input arrays and append them to the combinedVertices array.

This approach ensures that OpenGL receives a single index buffer with vertices that incorporate both vertex and normal data, resolving the issue of disparate indices for vertices and normals. It allows for correct rendering of meshes using glDrawArrays(GL_TRIANGLES,...) without the need for sorting vertices or duplicating vertices in the case of unique entries in the original vertex buffer.

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