Unity3D实现渐变颜色效果

using System;
using System.Collections.Generic;
using UnityEngine;
using UnityEngine.UI;
 
namespace ExtraFoundation.Components
{
 [AddComponentMenu("UI/Effects/Gradient")]
 public class UIGradient : BaseMeshEffect
 {
  #region Public Declarations
  public enum Type
  {
   Vertical,
   Horizontal
  }
  #endregion
 
  #region Public Properties
  public Type GradientType = Type.Vertical;
  [Range(-1f, 1f)]
  public float Offset = 0f;
  public Gradient gradient;
  #endregion
 
  #region Public Methods
  public override void ModifyMesh(VertexHelper helper)
  {
   if (!IsActive() || helper.currentVertCount == 0)
   {
    return;
   }
 
   vertexList.Clear();
   helper.GetUIVertexStream(vertexList);
 
   int nCount = vertexList.Count;
   switch (GradientType)
   {
    case Type.Vertical:
     {
      float fBottomY = vertexList[0].position.y;
      float fTopY = vertexList[0].position.y;
      float fYPos = 0f;
 
      for (int i = nCount - 1; i >= 1; --i)
      {
       fYPos = vertexList[i].position.y;
       if (fYPos > fTopY)
        fTopY = fYPos;
       else if (fYPos < fBottomY)
        fBottomY = fYPos;
      }
 
      float fUIElementHeight = 1f / (fTopY - fBottomY);
      UIVertex v = new UIVertex();
 
      for (int i = 0; i < helper.currentVertCount; i++)
      {
       helper.PopulateUIVertex(ref v, i);
       v.color = gradient.Evaluate((v.position.y - fBottomY) *
        fUIElementHeight - Offset);
       helper.SetUIVertex(v, i);
      }
     }
     break;
    case Type.Horizontal:
     {
      float fLeftX = vertexList[0].position.x;
      float fRightX = vertexList[0].position.x;
      float fXPos = 0f;
 
      for (int i = nCount - 1; i >= 1; --i)
      {
       fXPos = vertexList[i].position.x;
       if (fXPos > fRightX)
        fRightX = fXPos;
       else if (fXPos < fLeftX)
        fLeftX = fXPos;
      }
 
      float fUIElementWidth = 1f / (fRightX - fLeftX);
      UIVertex v = new UIVertex();
 
      for (int i = 0; i < helper.currentVertCount; i++)
      {
       helper.PopulateUIVertex(ref v, i);
       v.color = gradient.Evaluate((v.position.x - fLeftX) *
        fUIElementWidth - Offset);
       helper.SetUIVertex(v, i);
      }
 
     }
     break;
    default:
     break;
   }
  }
  #endregion
  
  #region Internal Fields
  private List<UIVertex> vertexList = new List<UIVertex>();
  #endregion
 }
}