Unity3D手游開發日記(9) - 互動草的效果

所謂互動草,就是角色跑動或者釋放技能,能影響草的擺動方向和幅度.

前面的文章早已經實現了風吹草動的效果,遲遲沒有在Unity上面做互動草,是因為以前我在端游項目做過一套太過於牛逼的方案.在CE3的互動草的基礎上擴展,效果好,但技術太復雜,效率開銷也特別高. 如果在手機上,就得做一套簡單高效的.

 

實現效果:從任意方向碰一下草,草就應該來回晃動,晃動幅度逐漸減小.多次觸碰,效果應該疊加.這樣的話就比較真實.

 

實現原理:用正玄波實現草來回擺動的簡諧運動,用指數衰減來模擬阻力

 

實現步驟:

1.每個草掛一個腳本,來處理力的效果疊加

 

    public class Force
    {
        public float m_Time = 0;
        public Vector4 m_Force;

        public Force(Vector4 force)
        {
            m_Force = force;
        }
    }

    public class GrassForce : MonoBehaviour
    {
        public List<Force> m_ForceList = null;
        public float m_WaveFrequency = 6.0f;
        public float m_Resistance = 0.25f;
        public float m_MaxForceMagnitude = 6.0f;
        public float m_AddForceTimeInterval = 0.5f;
        public int m_MaxForceNum = 3;

        private float m_LastAddTime = 0;
        private Material material;

        void Start()
        {
            material = gameObject.renderer.material;
        }

        void Update()
        {
            UpdateForce();
        }

        void OnBecameVisible()
        {
            enabled = true;
        }
        void OnBecameInvisible()
        {
            enabled = false;
        }

        public void AddForce(Vector3 force)
        {
            if (Time.time - m_LastAddTime > m_AddForceTimeInterval)
            {
                m_LastAddTime = Time.time;

                if (m_ForceList == null)
                    m_ForceList = new List<Force>();

                if (m_ForceList.Count < m_MaxForceNum)
                {
                    Vector4 newForce = new Vector4(force.x, 0, force.z, 0);
                    if (newForce.magnitude > m_MaxForceMagnitude)
                        newForce = newForce.normalized * m_MaxForceMagnitude;

                    m_ForceList.Add(new Force(newForce));
                }
            }
        }

        private void UpdateForce()
        {
            if (m_ForceList == null)
                return;

            Vector4 accForce = Vector4.zero;
            for (int i = m_ForceList.Count - 1; i >= 0; --i)
            {
                if (m_ForceList[i].m_Force.magnitude > 0.1f)
                {
                    // [-1, 1] 正玄波模擬簡諧運動
                    float wave_factor = Mathf.Sin(m_ForceList[i].m_Time * m_WaveFrequency);

                    // 力的指數衰減
                    float resistance_factor = easeOutExpo(1, 0, m_Resistance * Time.deltaTime);
                    m_ForceList[i].m_Force *= resistance_factor;

                    m_ForceList[i].m_Time += Time.deltaTime;

                    // 累加
                    accForce += m_ForceList[i].m_Force * wave_factor;
                }
                else
                {
                    m_ForceList.RemoveAt(i);
                }
            }

            if (accForce != Vector4.zero)
            {
                if (material.HasProperty("_Force"))
                {
                    accForce = transform.InverseTransformVector(accForce); // 世界空間轉換到模型本地空間
                    material.SetVector("_Force", accForce);
                }
            }
        }

        public float easeOutExpo(float start, float end, float value)
        {
            end -= start;
            return end * (-Mathf.Pow(2, -10 * value) + 1) + start;
        }
    }

2.如何確定哪些草受到影響,以及受力的方向?

 

 

public static void AddForceToGrass(int forceId, Transform transform)
{
    ForceTable force = ForceTableMgr.Instance.GetDataById(forceId);
    if (force != null)
    {
        Vector3 relativeCenter = new Vector3(force.RelativeCenterX, force.RelativeCenterY, force.RelativeCenterZ);
        Vector3 center = transform.TransformPoint(relativeCenter);
        //Vector3 size = new Vector3(force.Length, force.Height, force.Width);
        Vector3 size = new Vector3(force.Width, force.Height, force.Length);

        // 方向矩陣
        Matrix4x4 m44 = Matrix4x4.TRS(Vector3.zero, Quaternion.Inverse(transform.rotation), Vector3.one);

        PhysicsUtil.AddForceToGrass((RangeType)force.RangeType, (ForceDirType)force.DirType, force.Strength, center, size, transform.forward, m44, force.Degree);
    }
}

private static void AddForceToGrass(RangeType type, ForceDirType dirType, float strength, Vector3 center, Vector3 size, Vector3 direction, Matrix4x4 m44, float degree = 360.0f)
{
    if (type == RangeType.Sphere)
    {
        AddForceInSector(dirType, strength, center, size.x, direction, degree);
    }
    else if (type == RangeType.Cude)
    {
        AddForceInCube(dirType, strength, center, size, direction, m44, degree);
    }
}

草可以看成一個點,計算和下面范圍的相交.

 

1.圓形和扇形范圍

圓形范圍計算特別簡單,計算距離即可.扇形范圍只需要在圓形基礎上再計算一次夾角即可,部分核心代碼:

 

                    Vector3 dir = script.transform.position - center;
                    if (dir.sqrMagnitude <= radius * radius)
                    {
                        dir.y = 0;
                        if (Mathf.Abs(Vector3.Angle(dir, direction)) <= degree)
                        {
                            float factor = 0.25f + Mathf.Clamp01((radius - dir.magnitude) / radius) * 0.75f; // 衰減因子

                            Vector3 forceDir;
                            if (dirType == ForceDirType.ToTarget)
                                forceDir = dir.normalized;
                            else
                                forceDir = -dir.normalized;

                            script.AddForce(forceDir * factor * strength);
                        }
                    }

 

2.矩形范圍

點和任意方向的矩形的計算,這個比較難.Unity本身也沒提供此類相交API.不過熟悉引擎開發的應該知道AABB和OBB吧.其實矩形范圍計算,就是計算點和OBB的相交.

點和AABB的相交計算很簡單,因為AABB每條邊都是和坐標軸平行或者垂直的.而OBB有方向,其實只需要把點矩陣變換到OBB所在的空間,就可以用AABB的方法來計算了.

 

public struct AABB
{
    public Vector3 min;
    public Vector3 max;

    public AABB(Vector3 vmin, Vector3 vmax)
    {
        min = vmin;
        max = vmax;
    }
}

public struct OBB
{
    public Matrix4x4 m44;
    public Vector3 h;               // half-length-vector
    public Vector3 c;               // center of obb

    public OBB(Matrix4x4 mat44, Vector3 hlv, Vector3 center)
    {
        m44 = mat44;
        h = hlv;
        c = center;
    }

    public OBB(Matrix4x4 mat44, AABB aabb)
    {
        m44 = mat44;
        h = (aabb.max - aabb.min) * 0.5f;
        c = (aabb.max + aabb.min) * 0.5f;
    }
}

// 點和AABB的相交
public static bool Overlap_Point_AABB(Vector3 p, AABB aabb)
{
    return ((p.x >= aabb.min.x && p.x <= aabb.max.x) && (p.y >= aabb.min.y && p.y <= aabb.max.y) && (p.z >= aabb.min.z && p.z <= aabb.max.z));
}

// 點和OBB的相交
public static bool Overlap_Point_OBB(Vector3 p, Vector3 obbWorldPos, OBB obb)
{
    AABB aabb = new AABB(obb.c - obb.h, obb.c + obb.h);
    Vector3 local_p = p - obbWorldPos;
    Vector3 t = obb.m44.MultiplyVector(local_p);
    return Overlap_Point_AABB(t, aabb);
}

記住,OBB參數設置,中心一定要在世界原點,這樣才方便計算

 

 

// 包圍盒中心為世界原點.便於計算.
Vector3 min = - size * 0.5f;
Vector3 max = size * 0.5f;
AABB aabb = new AABB(min, max);
OBB obb = new OBB(m44, aabb);

相交和計算力方向:

 

 

if (PhysicsUtil.Overlap_Point_OBB(script.transform.position, center, obb))
{
    // 暫時只支持Left_Right
    if (dirType == ForceDirType.Left_Right)
    {
        Vector3 dir = script.transform.position - center;
        dir = m44.MultiplyVector(dir);
        dir = (dir.x < 0) ? m44.transpose.MultiplyVector(Vector3.left) : m44.transpose.MultiplyVector(Vector3.right);

        Vector3 force = dir.normalized * strength;
        script.AddForce(force);
    }
}

 

效果圖:

1.圓形范圍,力的方向從圓心到目標,模擬氣浪把把草震開.

2.矩形范圍,力的方向是玩家面向的左和右.模擬劍氣把草劈開的感覺.

 

效率優化:

1.控制互動草的數量,這種草不能合批,謹記.

2.腳本加上了OnBecameVisible,OnBecameInvisible 只讓攝像機內草起作用.