Unity – 渐变文字

【实现】

[AddComponentMenu("UI/Effects/Gradient")]
public class Gradient : BaseMeshEffect
{
    public enum Type
    {
        Horizontal,
        Vertical,
    }

    public enum Blend
    {
        Override,
        Add,
        Multiply,
    }

    [SerializeField]
    private Type m_GradientType = Type.Vertical;
    [SerializeField]
    private Blend m_BlendMode = Blend.Override;
    [SerializeField]
    [Range(-1, 1)]
    private float m_Offset = 0;
    [SerializeField]
    private UnityEngine.Gradient m_effectGradient 
    = new UnityEngine.Gradient()
    {
        colorKeys = new GradientColorKey[] { 
        new GradientColorKey(Color.black, 0),
        new GradientColorKey(Color.white, 1)}
    };

   private Text m_Text;

   protected override void OnEnable()
   {
       m_Text = GetComponent<Text>();
   }

   public override void ModifyMesh(VertexHelper helper)
   {
       if (!IsActive() || helper.currentVertCount == 0)
       return;

       List<UIVertex> vertexList = new List<UIVertex>();
       helper.GetUIVertexStream(vertexList);

       int count = vertexList.Count;
       switch (GradientType)
       {
       case Type.Horizontal:
           float left = vertexList[0].position.x;
           float right = vertexList[0].position.x;
           float x = 0;
           for (int i = count - 1; i >= 1; --i)
           {
               x = vertexList[i].position.x;

               if (x > right)
                   right = x;
               else if (x < left)
                   left = x;
           }

           float width = right - left;
           UIVertex vertex = new UIVertex();

           for (int i = 0; i < helper.currentVertCount; i++)
           {
               helper.PopulateUIVertex(ref vertex, i);

               vertex.color = BlendColor(vertex.color, 
                   EffectGradient.Evaluate((vertex.position.x - left) / width - Offset));
               vertex.color.a = (byte)(m_Text.color.a * 255);
               helper.SetUIVertex(vertex, i);
           }
           break;
       case Type.Vertical:
           float top = vertexList[0].position.y;
           float bottom = vertexList[0].position.y;
           float y = 0;
           for (int i = count - 1; i >= 1; --i)
           {
               y = vertexList[i].position.y;

               if (y > top)
                   top = y;
               else if (y < bottom)
                   bottom = y;
           }

           float height = top - bottom;
           UIVertex vertex2 = new UIVertex();

           for (int i = 0; i < helper.currentVertCount; i++)
           {
               helper.PopulateUIVertex(ref vertex2, i);

               vertex2.color = BlendColor(vertex2.color, 
                   EffectGradient.Evaluate((vertex2.position.y - bottom) / height - Offset));
               vertex2.color.a = (byte)(m_Text.color.a * 255);
               helper.SetUIVertex(vertex2, i);
           }
           break;
       }
   }

   Color BlendColor(Color colorA, Color colorB)
   {
       switch (BlendMode)
       {
           case Blend.Add:
               return colorA + colorB;
           case Blend.Multiply:
               return colorA * colorB;
           default:
               return colorB;
       }
   }
}

【问题】

1. 如果Text需要使用Outline和Shadow组件，需要将他们放在Gradient组件下面，否则上面两个组件的效果会被覆盖掉。
2. 由于我给字体添加了DotweenAnimation组件用于制作Text的透明度动画，所以Gradient组件需要更新自己的透明度，与Text组件中的值统一。（蓝字部分）

【参考】

1. Unity5.X中渐变字体的实现方法

2.Unity2017中渐变字体的实现方法