Unity UGUI 程序化网格 03：两个三角形组成矩形

// Assets/OnPopulateMeshBook/Chapters/Chapter03_Quad/
// Runtime/QuadGraphic.cs · QuadGraphic.OnPopulateMesh
using UnityEngine;
using UnityEngine.UI;

namespace OnPopulateMeshBook.Chapter03
{
    public sealed class QuadGraphic : Graphic
    {
        protected override void OnPopulateMesh(VertexHelper vh)
        {
            vh.Clear();
            var vertex = UIVertex.simpleVert;
            vertex.color = color;

            vertex.position = new Vector2(-60f, -40f);
            vh.AddVert(vertex);
            vertex.position = new Vector2(-60f, 40f);
            vh.AddVert(vertex);
            vertex.position = new Vector2(60f, 40f);
            vh.AddVert(vertex);
            vertex.position = new Vector2(60f, -40f);
            vh.AddVert(vertex);

            vh.AddTriangle(0, 1, 2);
            vh.AddTriangle(2, 3, 0);
        }
    }
}

// Artifacts/chapter03.json · 四边形固定网格
{
  "chapter": 3,
  "fixedInput": "indices=0,1,2,2,3,0",
  "components": [
    {
      "component": "QuadGraphic",
      "vertices": [
        { "x": -60.0, "y": -40.0, "z": 0.0 },
        { "x": -60.0, "y":  40.0, "z": 0.0 },
        { "x":  60.0, "y":  40.0, "z": 0.0 },
        { "x":  60.0, "y": -40.0, "z": 0.0 }
      ],
      "colors": [
        { "r": 255, "g": 183, "b": 77, "a": 255 },
        { "r": 255, "g": 183, "b": 77, "a": 255 },
        { "r": 255, "g": 183, "b": 77, "a": 255 },
        { "r": 255, "g": 183, "b": 77, "a": 255 }
      ],
      "indices": [0, 1, 2, 2, 3, 0]
    }
  ]
}

// 由固定顶点复算两组三角形的有向面积
static float SignedTwiceArea(
    Vector2 a, Vector2 b, Vector2 c)
{
    return (b.x - a.x) * (c.y - a.y)
         - (b.y - a.y) * (c.x - a.x);
}

var v0 = new Vector2(-60f, -40f);
var v1 = new Vector2(-60f, 40f);
var v2 = new Vector2(60f, 40f);
var v3 = new Vector2(60f, -40f);

Assert.That(SignedTwiceArea(v0, v1, v2), Is.EqualTo(-9600f));
Assert.That(SignedTwiceArea(v2, v3, v0), Is.EqualTo(-9600f));

// Assets/OnPopulateMeshBook/Chapters/Chapter03_Quad/
// Tests/Editor/QuadGraphicTests.cs
using NUnit.Framework;
using OnPopulateMeshBook.Chapter03;
using OnPopulateMeshBook.TestSupport;
using UnityEngine;

public sealed class QuadGraphicTests
{
    [Test]
    public void Populate_ProducesSharedVertexQuad()
    {
        var graphic = MeshTestSupport.CreateGraphic<QuadGraphic>(
            new Vector2(120f, 80f));
        var mesh = MeshTestSupport.Build(graphic);

        Assert.That(mesh.vertexCount, Is.EqualTo(4));
        Assert.That(mesh.triangles, Is.EqualTo(
            new[] { 0, 1, 2, 2, 3, 0 }));
        MeshTestSupport.AssertIndicesInRange(mesh);

        MeshTestSupport.Destroy(graphic, mesh);
    }
}

export UNITY_EDITOR="<Unity-2022.3.62f3-editor>"
"$UNITY_EDITOR" \
  -batchmode \
  -nographics \
  -projectPath "$PROJECT_ROOT/.tmp/unity-onpopulate-mesh-lab" \
  -runTests \
  -testPlatform EditMode \
  -testResults Artifacts/editmode-results.xml \
  -logFile Artifacts/editmode.log
echo "exit=$?"

exit=0
testcasecount=19
passed=19
failed=0
skipped=0
duration=0.0400379s

QuadGraphicTests.Populate_ProducesSharedVertexQuad
result=Passed
duration=0.000358s
vertexCount=4
indexCount=6
triangleCount=2
indices=[0,1,2,2,3,0]

vh.AddTriangle(0, 1, 2);
vh.AddTriangle(0, 1, 3); // 错误：重复使用左边，不沿对角线 0—2

// 数量仍为：
// vertexCount=4
// indexCount=6
// 但固定合同 [0,1,2,2,3,0] 已被破坏
// 修复：
vh.AddTriangle(2, 3, 0);

// 失败时序示意：容器已有上一轮 4 顶点、6 索引
// 省略 vh.Clear()
// 再 AddVert 四次 -> 顶点总数 8，新编号为 4..7
// 仍写 0,1,2,2,3,0 -> 再次引用旧编号

Assert.That(existingVertexCount, Is.EqualTo(4));
var appendedVertexCount = existingVertexCount + 4;
Assert.That(appendedVertexCount, Is.EqualTo(8));

// 修复：生成入口第一句恢复 vh.Clear()