deriveTangentsFor

function deriveTangentsFor(mesh: MeshData): MeshData

import { deriveTangentsFor } from '@driftengine/assets';

Parameters

In depth

The order is the point of this function existing. generateTangents accumulates a frame per index, so a vertex shared by several triangles gets the sum of all of them and comes out smooth — which is what it was written to do. Run on a mesh as a file stores it, and a great many files store one vertex per triangle corner, every corner is its own index and gets exactly one triangle's frame. Two corners at the same point then disagree, and the weld cannot merge them, because two corners alike in position, normal and UV but opposite in the bitangent's sign are a mirrored UV shell and merging those lights one side of a model inside out. Nothing can tell the two cases apart from the data.

Measured on a rotationally unwrapped corner soup, which is the shape a CAD conversion arrives in: 9,600 corners weld to 1,681 vertices with no frame present and to 9,482 with a frame derived per corner, with up to six different frames at one point. Deriving afterwards gives 1,681 vertices and one frame each, and the frame is better — averaged over every triangle at the vertex, which is the smoothing the derivation exists for and which a soup cannot supply.

A mesh that already carries a frame is returned untouched: authored data is the file's to state. A mesh with no texture coordinates is returned untouched too, since there is no texture direction to derive one along.