Chen Yulin's Blog

• Task
• Vehicle Physics Pro
  • Needs
  • Install
• GLTFUtility
  • Needs
  • Install
  • Runtime API
  • Trouble shooting
• Csharp’s interpretation of Json
• Abstract the vehicle as a Json structure
  • Graph
  • Json example

Task

• Load car configuration from .json file
• Compose DevDocs
• Investigate csharp comment documentation
• use assimp to load .glb model

---

Vehicle Physics Pro

Starting point
The unity’s build-in physics engine PhysX is far from being precise enough for a vehicle simulator.

Needs

• Closer to reality vehicle physics
• Runtime performance
• Not so complicated to config so that the composition of the savings and editor will not be a headache

Official

Install

Through Asset Store

---

GLTFUtility

Starting point
The car model should be customizable, i.e. the user drag a car model into a directory and the game should be able to load it.
Filetype .glb is nice but unity doesn’t have build-in support

Needs

• Runtime import
• support mesh and material

GLTFUtility

Install

In tactics project:

git submodule add https://github.com/Siccity/GLTFUtility.git ./Tactics/Assets/ThirdParty/GLTFUtility

Runtime API

using Siccity.GLTFUtility

// Single thread
void ImportGLTF(string filepath){
    GameObject res = Importer.LoadFromFile(filepath);
}

// Multi thread
void ImportGLTFAsync(string filepath){
    Importer.ImportGLTFAsync(filepath, new ImportSettings(), OnFinish);
}
void OnFinish(){
    ...
}

here I use Application.streamingAssetsPath+"/Model/"+JsonReader.vehicle.model.carBody[0].dir as filepath

Trouble shooting

1. In the built game, encounter ArgumentNullException: Value cannot be null. Parameter name: shader
   Github Issue
2. The file management of the game changed after being built. How to determine where to place the Save and Model folders?
   Use Application.streamingAssetsPath, stands for Assets/StreamingAssets in Unity editor and Game_Data/StreamingAssets in exported game.

---

Csharp’s interpretation of Json

First construct the structure of the json file in c#.
Notice: the name of the member variable should be the same with those in json file

[System.Serializable]
public class VehiclePhysicsPara
{
    public float bodyMass;
    public Vector3 centerOfMass;
    public List<BodyColliderPara> collider;
    public List<WheelColliderPara> wheel;
}

[System.Serializable]
public class BodyColliderPara
{
    public string type; // box | sphere
    public Vector3 position;
    public Vector3 eulerRotation;
    public Vector3 scale;
}
[System.Serializable]
public class SteeringWheelTypePara
{
    public bool use;
    public bool inverse;
}
[System.Serializable]
public class WheelTypePara
{
    public bool powered;
    public SteeringWheelTypePara steering;
}
[System.Serializable]
public class WheelSuspensionPara
{
    public float spring;
    public float damper;
    public float distance;
    public float initialPosition;
}
[System.Serializable]
public class WheelFrictionPara
{
    public float extremumSlip;
    public float extremumValue;
    public float AsymptoteSlip;
    public float AsymptoteValue;
}

[System.Serializable]
public class WheelColliderPara
{
    public WheelTypePara type;
    public float mass;
    public float radius;
    public Vector3 position;
    public WheelSuspensionPara suspension;
    public WheelFrictionPara forwardFriction;
    public WheelFrictionPara sidewayFriction;
}

[System.Serializable]
public class VehicleModelPara
{
    public List<CarBodyPara> carBody;
    public List<WheelModelPara> wheel;
}
[System.Serializable]
public class CarBodyPara
{
    public string name;
    public string dir;
    public Vector3 position;
    public Vector3 eulerRotation;
    public Vector3 scale;
    public string shader;
}
[System.Serializable]
public class WheelModelPara
{
    public string name;
    public string dir;
    public Vector3 scale;
    public string shader;
}
[System.Serializable]
public class VehiclePara
{
    public VehicleModelPara model;
    public VehiclePhysicsPara physics;  
}

Notice: [System.Serializable] is for serialized display in Unity editor.

Then, directly use build-in json loader:

VehiclePara vehicle;
vehicle = JsonUtility.FromJson<VehiclePara>(textJson.text);

All the parameters will be stored in the instance vehicle .

---

Abstract the vehicle as a Json structure

Graph

flowchart RL
    Main
    Model --> Main
    Physics --> Main
    Controller --> Main
    carBody --> Model
    subgraph bodyPart
    part1
    part2
    end
    bodyPart --> carBody
    wheelVis --> Model
    wheelVisGroup --> wheelVis
    subgraph bodyCollider
        boxCol
        sphereCol
    end
    bodyCollider --> collider
    collider --> Physics
    massProperty --> Physics
    wheelProperty --> Physics
    wheelColGroup --> wheelProperty
    subgraph wheelVisGroup
        tyreVis1
        tyreVis2
        tyreVis3
        tyreVis4
    end
    subgraph wheelColGroup
        wheelCol1 
        wheelCol2 
        wheelCol3 
        wheelCol4 
    end
    wheelVisGroup -- oneToOne --> wheelColGroup
    

Json example

{
    "model":{
        "carBody":[
            {
                "name":"body1",
                "dir":"./CustomModel/car1/body1.obj",
                "position":{"x":0,"y":0,"z":0},
                "eulerRotation":{"x":0,"y":0,"z":0},
                "scale":{"x":0,"y":0,"z":0},
                "shader":"Standard"
            },
            {
                "name":"body2",
                "dir":"./CustomModel/car1/body2.obj",
                "position":{"x":0,"y":0,"z":0},
                "eulerRotation":{"x":0,"y":0,"z":0},
                "scale":{"x":0,"y":0,"z":0},
                "shader":"Standard"
            }
        ],
        "wheel":[
            {
                "name":"wheel1",
                "dir":"./CustomModel/car1/wheel1.obj",
                "scale":{"x":0,"y":0,"z":0},
                "shader":"Standard"
            }
        ]
    },
    "physics":{
        "collider":[
            {
                "type":"box",
                "position":{"x":0,"y":0,"z":0},
                "eulerRotation":{"x":0,"y":0,"z":0},
                "scale":{"x":0,"y":0,"z":0}
            },
            {
                "type":"sphere",
                "position":{"x":0,"y":0,"z":0},
                "eulerRotation":{"x":0,"y":0,"z":0},
                "scale":{"x":0,"y":0,"z":0}
            }
        ],
        "centerOfMass":{"x":0,"y":0,"z":0},
        "bodyMass":700,
        "wheel":[
            {
                "type":{"powered":true,"steering":{"use":true,"inverse":false}},
                "mass":7,
                "radius":0.5,
                "position":{"x":0,"y":0,"z":0},
                "suspension":{
                    "spring":25000,
                    "damper":9000,
                    "distance":0.3,
                    "initialPosition":0.5
                },
                "forwardFriction":{
                    "extremumSlip":0.1,
                    "extremumValue:":1,
                    "AsymptoteSlip":0.2,
                    "AsymptoteValue":0.8
                },
                "sidewayFriction":{
                    "extremumSlip":0.05,
                    "extremumValue:":1,
                    "AsymptoteSlip":0.2,
                    "AsymptoteValue":0.8
                }
            }
        ]
    }
}