Gradient.cs

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

namespace UIGradient
{
	[AddComponentMenu("UI/Effects/Gradient")]
	public class Gradient : BaseMeshEffect
	{

		public enum Type
		{
			Vertical,
			Horizontal
		}

		// TODO: Evaluate actual gradient instead
		[SerializeField] public UnityEngine.Gradient gradientTest;
		[SerializeField] public Type GradientType = Type.Vertical;
		[SerializeField]
		[Range(-1.5f, 1.5f)]
		public float Offset = 0f;
		[SerializeField] private Color32 StartColor = Color.white;
		[SerializeField] private Color32 EndColor = Color.black;

		public override void ModifyMesh(VertexHelper vh)
		{
			if (!IsActive()) return;

			List<UIVertex> list = new List<UIVertex>();

			vh.GetUIVertexStream(list);
			ModifyVertices(list);
			vh.Clear();
			vh.AddUIVertexTriangleStream(list);
		}

		public void ModifyVertices(List<UIVertex> _vertexList)
		{
			if (!IsActive()) return;

			int nCount = _vertexList.Count;

			switch (GradientType)
			{
				case Type.Vertical:
					{
						if (_vertexList.Count != 0)
						{
							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);

							for (int i = nCount - 1; i >= 0; --i)
							{
								UIVertex uiVertex = _vertexList[i];
								uiVertex.color = Color32.Lerp(EndColor, StartColor, (uiVertex.position.y - fBottomY) * fUIElementHeight - Offset);

								// TODO: Evaluate actual gradient instead
								//uiVertex.color = (Color32)gradientTest.Evaluate((uiVertex.position.y - fBottomY) * fUIElementHeight - Offset);
								// Tell people at https://forum.unity.com/threads/how-to-text-gradient-fill.268509/

								_vertexList[i] = uiVertex;
							}
						}
					}
					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);

						for (int i = nCount - 1; i >= 0; --i)
						{
							UIVertex uiVertex = _vertexList[i];
							uiVertex.color = Color32.Lerp(StartColor, EndColor, (uiVertex.position.x - fLeftX) * fUIElementWidth - Offset);
							_vertexList[i] = uiVertex;
						}
					}
					break;
				default:
					break;
			}
		}
	}
}