用法

将颜色渐变组件挂在Text所属GameObject上。（若有描边、阴影等组件，为了使这些组件的功能仍起效，需让颜色渐变组件在这些组件之上）
颜色渐变组件 可设置如下参数

1. 渐变方向：竖直 或 水平
2. 颜色叠加模式：覆盖、相加、相乘
3. 渐变偏移

4. 渐变色

   
   image.png

颜色渐变组件 代码

using System.Collections;
using System.Collections.Generic;
using UnityEngine;

namespace UnityEngine.UI
{
    [AddComponentMenu("UI/Effects/Gradient")]
    public class UiGradient : BaseMeshEffect
    {
        [SerializeField]
        private DirType _dir = DirType.Vertical;
        [SerializeField]
        private BlendType _blend = BlendType.Override;
        [SerializeField, Range(-1, 1)]
        private float _offset = 0f;
        [SerializeField]
        private Gradient _gradient = new Gradient(){ colorKeys = new GradientColorKey[] { new GradientColorKey(Color.black, 0), new GradientColorKey(Color.white, 1) } };

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

            var vertexs = new List<UIVertex>();
            vh.GetUIVertexStream(vertexs);

            bool isX = true;
            switch (_dir)
            {
                case DirType.Horizontal:
                    isX = true;
                    break;
                case DirType.Vertical:
                    isX = false;
                    break;
                default:
                    break;
            }

            var inverseLength = GetInverseLength(vertexs, isX, out float min, out float max);

            var vertex = new UIVertex();
            for (int i = 0; i < vh.currentVertCount; i++)
            {
                vh.PopulateUIVertex(ref vertex, i);
                vertex.color = BlendColor(vertex.color, _gradient.Evaluate((isX ? (vertex.position.x - min): (vertex.position.y - min)) * inverseLength - _offset), _blend);
                vh.SetUIVertex(vertex, i);
            }

        }

        // 若isX是false，则认为是y
        private float GetInverseLength(List<UIVertex> vertexs, bool isX, out float min, out float max)
        {
            float inverseLength = 0;
            min = isX ? vertexs[0].position.x : vertexs[0].position.y;
            max = min;
            for (int i = 1; i < vertexs.Count; i++)
            {
                var temp = isX ? vertexs[i].position.x : vertexs[i].position.y;

                if (temp > max)
                {
                    max = temp;
                }
                else if (temp < min)
                {
                    min = temp;
                }
            }

            inverseLength = 1 / (max - min);
            return inverseLength;
        }

        private Color BlendColor(Color originalColor, Color newColor, BlendType blendType)
        {
            var ret = newColor;
            switch (blendType)
            {
                case BlendType.Override: ret = newColor; break;
                case BlendType.Add: ret = originalColor + newColor; break;
                case BlendType.Multiply: ret = originalColor * newColor; break;
                default:break;
            }

            return ret;
        }

        private enum DirType
        { 
            None,
            Horizontal,
            Vertical,
        }

        private enum BlendType
        { 
            None,
            Override,
            Add,
            Multiply
        }
    }
}