Merge pull request #8216 from tdurand/fix-objserializer-handedness

Fix OBJ serializing mirrored

dist/preview release/what's new.md

@@ -208,6 +208,7 @@
 - Fixed `Sound` not accepting a `TransformNode` as a source for spatial sound ([Poolminer](https://github.com/Poolminer))
 - Fixed an issue with transformation set after physics body was created using cannon.js ([#7928](https://github.com/BabylonJS/Babylon.js/issues/7928)) ([RaananW](https://github.com/RaananW))
 - Fix bug when using `ShadowOnlyMaterial` with Cascaded Shadow Map and `autoCalcDepthBounds` is `true` ([Popov72](https://github.com/Popov72))
+- Fix OBJ serializer default scene scene handedness causing [OBJ Mirror export](https://forum.babylonjs.com/t/obj-export-mirrored/10835/10)
 - Fix bug when using shadows + instances + transparent meshes + `transparencyShadow = false` ([Popov72](https://github.com/Popov72))
 
 ## Breaking changes

serializers/src/OBJ/objSerializer.ts

@@ -67,7 +67,13 @@ export class OBJExport {
             }
 
             for (var i = 0; i < trunkVerts.length; i += 3) {
-                output.push("v " + trunkVerts[i] + " " + trunkVerts[i + 1] + " " + trunkVerts[i + 2]);
+                // Babylon.js default is left handed, while OBJ default is right handed
+                // Need to invert Z vertices unless Babylon is set to use a right handed system
+                if (mesh[0].getScene().useRightHandedSystem) {
+                    output.push("v " + trunkVerts[i] + " " + trunkVerts[i + 1] + " " + trunkVerts[i + 2]);
+                } else {
+                    output.push("v " + trunkVerts[i] + " " + trunkVerts[i + 1] + " " + -trunkVerts[i + 2]);
+                }
                 curV++;
             }