via @ondys –
A simple cube mode with normal map that simulates flat shading:
The cube has smooth geometry normals (no normal seams on cube edges) + a normal map that simulates flat shading.
|threejs flat||babylonjs flat|
Babylon.js rendering seems to work correctly but three.js produces a weird looking result (cesium viewer also seem to work correctly)
For comparison, if normal map is set to a constant value (128, 128, 255), the resulting geometry is smooth for both three.js and babylon.js:
|threejs smooth||babylonjs smooth|
Cube with constant normal map is here: