obj splits performance

v1.1.2

obj splits performance

obj file encoding and split obj

• add encoding support for obj and mtl files
• add an option to split obj model to multi models, so 1 obj can generate multi tiles for better responsiveness.

support more than 4 vertices for faces and generate MetallicRoughness material

1. Generate MetallicRoughness material, model is brighter now
2. Support face with more than 4 vertices
3. Fix "Material is incompatible with mesh primitive: Texture binding needs 'TEXCOORD_0' attribute."

fix a gltf invalid problem

1. object group's faces may have different mats, which causes gltf file to be invalid. Now mat grouped faces will be given a batchid.
2. generate tileset.json for every b3dm file in merging, so a single b3dm file can be loaded in cesium.
3. change some api, like that lod now is a method parameter for TileConverter.

fix some obj parse problems

1. fix obj mat Ks as double; support some faces have uvs but others not have
2. fix empty array problem when there is no texture.
3. support 4 vertex face, given default color if Ka and Kd not presented, if color value is greater than 1, scale it with max value.
4. fix transparency problem if dissolve value (d) set to 0

basic version release

Convert to:

• gltf/glb
• 3d tiles(b3dm) with batch ids

Obj file limitations:

1. one mtl file
2. all faces should be triangles already
3. only convert ka, kd, map_ka, map_kd, Ns, d material info