致力于赛车性能算法已有多时,在确定赛车最终版本之时,做下总结。
文章还是不会非常详尽,点到为指,不想太多利用工作时间。
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在制作前,必须先了解真实车辆的原理:
车辆分前轮驱动,后轮驱动和四驱动。动力由引擎提供,反应的力到轮胎上,因此产生转数,即RPM。
引擎的功率可以由RPM得到公式为 : RPM = 引擎功率×60/2×pi , 这些都是模拟,只为了更好的为下面的动作服务。还有大众关心的“漂移” ,所谓 漂移就是,在后驱车辆中,前轮方向旋转大角度,地面给于一定向心力,同时后轮又给予更多动力,导致“漂移”动作。
- void SuspensionHoldForce()
- {
- float fullCompressionSpringForce = this.rigidbody.mass * 0.25f * 2.0f * -Physics.gravity.y;
- this.OnGround = true;
- foreach( GameObject item in FwheelModels )
- {
- RaycastHit hit;
- bool onGround = Physics.Raycast( item.transform.parent.position , -item.transform.parent.InverseTransformDirection(Vector3.up), out hit, this.suspensionTravel + this.radius);
- if (onGround && hit.collider.isTrigger)
- {
- onGround = false;
- float dist = this.suspensionTravel + this.radius;
- RaycastHit[] hits = Physics.RaycastAll( item.transform.parent.position , -item.transform.parent.InverseTransformDirection(Vector3.up) , this.suspensionTravel + this.radius );
- foreach(RaycastHit test in hits)
- {
- if (!test.collider.isTrigger && test.distance <= dist)
- {
- hit = test;
- onGround = true;
- dist = test.distance;
- }
- }
- }
- if( onGround )
- {
- Vector3 wheelVelo = this.rigidbody.GetPointVelocity (item.transform.parent.position);
- Vector3 localVelo = transform.InverseTransformDirection (wheelVelo);
- Vector3 groundNormal = transform.InverseTransformDirection (hit.normal);
- float damperForce = Vector3.Dot(localVelo, groundNormal) * 5000f;
- float compression = 1.0f - ((hit.distance - radius) / suspensionTravel);
- Vector3 springForce = ( fullCompressionSpringForce*compression - damperForce ) * item.transform.parent.InverseTransformDirection(Vector3.up);
- springForce.z = springForce.x = 0f;
- this.rigidbody.AddForceAtPosition( springForce , item.transform.parent.position );
- }
- else
- {
- this.OnGround = false;
- }
- }
- foreach( GameObject item in BwheelModels )
- {
- RaycastHit hit;
- bool onGround = Physics.Raycast( item.transform.parent.position, -item.transform.parent.InverseTransformDirection(Vector3.up), out hit, this.suspensionTravel + this.radius);
- if (onGround && hit.collider.isTrigger)
- {
- onGround = false;
- float dist = this.suspensionTravel + this.radius;
- RaycastHit[] hits = Physics.RaycastAll( item.transform.parent.position, -item.transform.parent.InverseTransformDirection(Vector3.up) , this.suspensionTravel + this.radius );
- foreach(RaycastHit test in hits)
- {
- if (!test.collider.isTrigger && test.distance <= dist)
- {
- hit = test;
- onGround = true;
- dist = test.distance;
- }
- }
- }
- if( onGround )
- {
- Vector3 wheelVelo = this.rigidbody.GetPointVelocity (item.transform.parent.position);
- Vector3 localVelo = transform.InverseTransformDirection (wheelVelo);
- Vector3 groundNormal = transform.InverseTransformDirection (hit.normal);
- float damperForce = Vector3.Dot(localVelo, groundNormal) * 5000f;
- float compression = 1.0f - ( ( hit.distance - radius ) / suspensionTravel );
- Vector3 springForce = ( fullCompressionSpringForce*compression - damperForce ) * item.transform.parent.InverseTransformDirection(Vector3.up);
- springForce.z = springForce.x = 0f;
- this.rigidbody.AddForceAtPosition( springForce , item.transform.parent.position );
- }
- else
- {
- this.OnGround = false;
- }
- }
- }
这里也有2种方法:一个方向是真实车辆行驶轨迹,另一个是模拟型车辆轨迹。
前者的方法是 , 将动力点放在车辆驱动轮上,例如后轮。用rigidbody的 AddForceAtPosition可以做到,前轮只需要提供横向力就可以实现转弯的轨迹。但别看说说这么容易,这里面还涉及非常多的数值和曲线问题。在提供车辆动力时,你需要一条曲线,以致车辆不会匀加速,因为这样很不真实,还有在前轮横向力中,你必需是条由0到最高点,然后下降到平衡点的曲线。这样你的赛车才显得更真实。这些都需要用到几个数学知识。
后者,是用算法来模拟的一种车辆轨迹。这个算法所有作用力作用在车辆的中心点。
转弯轨迹,我是用转弯半径来表示,使得车辆在转弯时有相当的真实性,必须改变车辆转弯速度。当然,用到了些数学知识。代码奉献下:
- #region 计算转弯角度
- void Steering( bool canSteer , Vector3 relativeVelocity )
- {
- if( canSteer && this.OnGround )
- {
- if( this.shiftthrottle == 1 )
- {
- this.transform.RotateAround( this.transform.TransformPoint( ( this.FwheelModels[0].transform.localPosition + this.FwheelModels[1].transform.localPosition) * 0.5f ) , this.transform.up , this.rigidbody.velocity.magnitude *2f* this.steeringInput * Time.deltaTime * 2f );
- //~ this.rigidbody.AddForceAtPosition( this.FwheelModels[0].transform.TransformDirection(Vector3.right*this.steeringInput) * 3f * this.rigidbody.mass, this.FwheelModels[0].transform.position);
- //~ this.rigidbody.AddForceAtPosition( this.FwheelModels[1].transform.TransformDirection(Vector3.right*this.steeringInput) * 3f * this.rigidbody.mass, this.FwheelModels[1].transform.position);
- return ;
- }
- if( this.throttle * this.transform.InverseTransformDirection(this.rigidbody.velocity).z < 0 )
- return ;
- float turnRadius = 3.0f / Mathf.Sin( (90f - this.steering) * Mathf.Deg2Rad );
- float minMaxTurn = EvaluateSpeedToTurn(this.rigidbody.velocity.magnitude);
- float turnSpeed = Mathf.Clamp(relativeVelocity.z / turnRadius, -minMaxTurn / 10, minMaxTurn / 10);
- this.transform.RotateAround( this.transform.position + this.transform.right * turnRadius * this.steeringInput , transform.up , turnSpeed * Mathf.Rad2Deg * Time.deltaTime * this.steeringInput );
- //~ Vector3 debugStartPoint = transform.position + transform.right * turnRadius * this.steeringInput;
- //~ Vector3 debugEndPoint = debugStartPoint + Vector3.up * 5f;
- //~ Debug.DrawLine(debugStartPoint, debugEndPoint, Color.red);
- }
- }
- float EvaluateSpeedToTurn( float speed )
- {
- if(speed > this.topSpeed / 2)
- return minimumTurn;
- float speedIndex = 1 - ( speed / ( this.topSpeed / 2 ) );
- return minimumTurn + speedIndex * (maximumTurn - minimumTurn);
- }
- #endregion
这个模拟车辆轨迹,不能达到漂移的性能,但我加了一个滑动比例计算的算法,用车辆横向移动速度,和前进速度,的比例来确定,该车辆是否处于漂移状态,如处于,则启动漂移滑动程序。当然,我的赛车是很自然的,不做做。至于轮胎痕迹,就是判断是否触底后,在该点生成轮胎痕迹gameobject,如此而已。
最后,再介绍下,所有车辆都需要模拟的,行驶时,轮胎随速度旋转这个关系到车辆看起来真实性的东西。其实非常简单。不多说,发代码:
- #region 轮胎滚动与旋转模拟
- void WheelRoll()
- {
- float averageAngularVelo = ( this.rigidbody.GetPointVelocity(this.BwheelModels[0].transform.parent.position).magnitude + this.rigidbody.GetPointVelocity(this.BwheelModels[0].transform.parent.position).magnitude )/2f;
- float engineAngularVelo = averageAngularVelo * 3f;
- float rpm = engineAngularVelo * (60.0f/(2*Mathf.PI)) * (this.transform.InverseTransformDirection(this.rigidbody.velocity).z > 0f ? 1f : -1f );
- //~ Debug.Log(this.transform.InverseTransformDirection(this.rigidbody.velocity).z);
- FwheelModels[0].transform.rotation = FwheelModels[0].transform.parent.rotation * Quaternion.Euler (RotationValue, this.steering , 0);//旋转
- FwheelModels[1].transform.rotation = FwheelModels[1].transform.parent.rotation * Quaternion.Euler (RotationValue, this.steering , 0);//旋转
- BwheelModels[0].transform.rotation = BwheelModels[0].transform.parent.rotation * Quaternion.Euler (RotationValue, 0, 0);//旋转
- BwheelModels[1].transform.rotation = BwheelModels[1].transform.parent.rotation * Quaternion.Euler (RotationValue, 0, 0);//旋转
- RotationValue += rpm * ( 360f/60f ) * Time.deltaTime;
- }