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Document coordinate system change at top of source

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JosiahWI 2023-05-17 13:23:53 -05:00 committed by Josiah VanderZee
parent 8c9a5764ee
commit 5f5dd7abfc
1 changed files with 11 additions and 4 deletions
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15
source/Irrlicht/CGLTFMeshFileLoader.cpp
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@ -22,6 +22,17 @@
#include <utility>
#include <vector>
/* Notes on the coordinate system.
*
* glTF uses a right-handed coordinate system where +Z is the
* front-facing axis, and Irrlicht uses a left-handed coordinate
* system where -Z is the front-facing axis.
* We convert between them by reflecting the mesh across the X axis.
* Doing this correctly requires negating the Z coordinate on
* vertex positions and normals, and reversing the winding order
* of the vertex indices.
*/
// A helper function to disable tinygltf embedded image loading
static bool dummyImageLoader(tinygltf::Image *a,
const int b, std::string *c,
@ -115,8 +126,6 @@ IAnimatedMesh* CGLTFMeshFileLoader::createMesh(io::IReadFile* file)
meshIndex,
primitiveIndex);
// Inverse the order of indices due to the axis of the model being
// inverted when going from left handed to right handed coordinates
std::reverse(indicesBuffer.begin(),indicesBuffer.end());
// Create the mesh buffer
@ -217,8 +226,6 @@ core::vector3df CGLTFMeshFileLoader::ModelParser::readVec3DF(
const BufferOffset& readFrom,
const float scale = 1.0f)
{
// glTF's coordinate system is right-handed, Irrlicht's is left-handed
// glTF's +Z axis corresponds to Irrlicht's -Z axis
return core::vector3df(
scale * readPrimitive<float>(readFrom),
scale * readPrimitive<float>(BufferOffset(readFrom, sizeof(float))),