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Added tangent handedness to glTF export (#6322)

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* Added tangent handedness to glTF export
This commit is contained in:
Luca Della Vedova
2025-09-18 20:10:41 +08:00
committed by GitHub
parent 5c568616ec
commit 0581ed5f11
1 changed files with 16 additions and 3 deletions
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19
code/AssetLib/glTF2/glTF2Exporter.cpp
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@@ -59,6 +59,7 @@ OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
// Header files, standard library.
#include <cinttypes>
#include <cmath>
#include <limits>
#include <memory>
#include <iostream>
@@ -1238,13 +1239,25 @@ void glTF2Exporter::ExportMeshes() {
}
/******************** Tangents ********************/
if (nullptr != aim->mTangents) {
if (nullptr != aim->mTangents && nullptr != aim->mBitangents) {
// Find the handedness by calculating the bitangent without the handedness factor,
// the use a dot product to find out if the original bitangent was inverted (multiplied
// by a factor of -1.0) or not (multiplied by 1.0)
std::vector<ai_real> tangentsWithHandedness(aim->mNumVertices * 4);
for (uint32_t i = 0; i < aim->mNumVertices; ++i) {
aiVector3D calculatedBitangent = aim->mNormals[i] ^ aim->mTangents[i];
ai_real bitangentDotProduct = calculatedBitangent * aim->mBitangents[i];
ai_real handedness = std::copysign(1.0, bitangentDotProduct);
aim->mTangents[i].NormalizeSafe();
tangentsWithHandedness[i * 4] = aim->mTangents[i][0];
tangentsWithHandedness[i * 4 + 1] = aim->mTangents[i][1];
tangentsWithHandedness[i * 4 + 2] = aim->mTangents[i][2];
tangentsWithHandedness[i * 4 + 3] = handedness;
}
Ref<Accessor> t = ExportData(
*mAsset, meshId, b, aim->mNumVertices, aim->mTangents, AttribType::VEC3,
AttribType::VEC3, ComponentType_FLOAT, BufferViewTarget_ARRAY_BUFFER
*mAsset, meshId, b, aim->mNumVertices, &tangentsWithHandedness[0], AttribType::VEC4,
AttribType::VEC4, ComponentType_FLOAT, BufferViewTarget_ARRAY_BUFFER
);
if (t) {
p.attributes.tangent.push_back(t);