using UnityEngine;
using UnityEngine.UI;
using System.Collections.Generic;
/// <summary>
/// 特殊3段变色，上段和下段为纯色，中段有渐变效果
/// </summary>
public class UIGradient3Slice : BaseMeshEffect
{
    public Color topColor = Color.white;
    public Color bottomColor = Color.black;
    public float topHeight = 0.225f;
    public float bottomHeight = 0.225f;
    
    public override void ModifyMesh(VertexHelper vh)
    {
        if (!IsActive())
            return;
        List<UIVertex> vertList = new List<UIVertex>(vh.currentVertCount);
        vh.GetUIVertexStream(vertList);
        vh.Clear();
        // 按每四个顶点为一个四边形
        for (int i = 0; i < vertList.Count; i += 6)
        {
            // 分解为8个顶点
            UIVertex top_0 = vertList[i];
            UIVertex top_1 = vertList[i + 1];
            UIVertex bottom_0 = vertList[i + 4];
            UIVertex bottom_1 = vertList[i + 2];
            UIVertex midUp_0 = LerpVertex(bottom_0, top_0, 1f - topHeight);
            UIVertex midUp_1 = LerpVertex(bottom_1, top_1, 1f - topHeight);
            UIVertex midDown_0 = LerpVertex(bottom_0, top_0, bottomHeight);
            UIVertex midDown_1 = LerpVertex(bottom_1, top_1, bottomHeight);
            top_0.color = topColor;
            top_1.color = topColor;
            midUp_0.color = topColor;
            midUp_1.color = topColor;
            midDown_0.color = bottomColor;
            midDown_1.color = bottomColor;
            bottom_0.color = bottomColor;
            bottom_1.color = bottomColor;
            // 重新组装为3个四边形
            WriteQuad(vh, top_0, top_1, midUp_0, midUp_1);
            WriteQuad(vh, midUp_0, midUp_1, midDown_0, midDown_1);
            WriteQuad(vh, midDown_0, midDown_1, bottom_0, bottom_1);
        }
    }
    public UIVertex LerpVertex(UIVertex a, UIVertex b, float ratio)
    {
        UIVertex result = new UIVertex();
        result.position = Vector3.Lerp(a.position, b.position, ratio);
        result.uv0 = Vector3.Lerp(a.uv0, b.uv0, ratio);
        result.uv1 = Vector3.Lerp(a.uv1, b.uv1, ratio);
        result.normal = Vector3.Lerp(a.normal, b.normal, ratio);
        result.tangent = Vector3.Lerp(a.tangent, b.tangent, ratio);
        return result;
    }
    public void WriteQuad(VertexHelper vh, UIVertex top_0, UIVertex top_1, UIVertex bottom_0, UIVertex bottom_1)
    {
        int startIndex = vh.currentVertCount;
        vh.AddVert(top_0);
        vh.AddVert(top_1);
        vh.AddVert(bottom_1);
        vh.AddVert(bottom_0);
        vh.AddTriangle(startIndex, startIndex + 1, startIndex + 2);
        vh.AddTriangle(startIndex, startIndex + 3, startIndex + 2);
    }
}