Unity UGUI 程序化网格 06：UV 坐标如何映射一张纹理

本文输入合同
v0 左下 position -> uv(0,0)
v1 左上 position -> uv(0,1)
v2 右上 position -> uv(1,1)
v3 右下 position -> uv(1,0)
texture = fixed 4x4 checker
indices = 0,1,2, 2,3,0

Inspector 固定值
RectTransform = 420 x 240
Pivot         = (0.5, 0.5)
Color         = RGBA(255,255,255,255)
Texture       = Checker4x4

corner mapping:
texture bottom-left -> rect bottom-left
texture top-left    -> rect top-left
texture top-right   -> rect top-right
texture bottom-right-> rect bottom-right

position                    uv
(-210,-120) left-bottom     (0,0)
(-210, 120) left-top        (0,1)
( 210, 120) right-top       (1,1)
( 210,-120) right-bottom    (1,0)

position rectangle size = 420 x 240 local units
uv rectangle size       = 1 x 1 normalized units

// Assets/OnPopulateMeshBook/Chapters/Chapter06_UV/
// Runtime/TextureQuadGraphic.cs · TextureQuadGraphic
using UnityEngine;
using UnityEngine.UI;

namespace OnPopulateMeshBook.Chapter06
{
    public sealed class TextureQuadGraphic : Graphic
    {
        [SerializeField] private Texture texture;

        public override Texture mainTexture =>
            texture == null ? s_WhiteTexture : texture;

        public void SetTexture(Texture value)
        {
            if (texture == value) return;
            texture = value;
            SetMaterialDirty();
        }

        protected override void OnPopulateMesh(VertexHelper vh)
        {
            vh.Clear();
            var rect = GetPixelAdjustedRect();
            if (rect.width <= 0f || rect.height <= 0f) return;
            AddVertex(vh,
                new Vector2(rect.xMin, rect.yMin),
                new Vector2(0f, 0f));
            AddVertex(vh,
                new Vector2(rect.xMin, rect.yMax),
                new Vector2(0f, 1f));
            AddVertex(vh,
                new Vector2(rect.xMax, rect.yMax),
                new Vector2(1f, 1f));
            AddVertex(vh,
                new Vector2(rect.xMax, rect.yMin),
                new Vector2(1f, 0f));
            vh.AddTriangle(0, 1, 2);
            vh.AddTriangle(2, 3, 0);
        }

        private void AddVertex(
            VertexHelper vh, Vector2 position, Vector2 uv)
        {
            var vertex = UIVertex.simpleVert;
            vertex.position = position;
            vertex.color = color;
            vertex.uv0 = uv;
            vh.AddVert(vertex);
        }
    }
}

// Assets/OnPopulateMeshBook/Chapters/Chapter06_UV/
// Tests/Editor/TextureQuadGraphicTests.cs
using NUnit.Framework;
using OnPopulateMeshBook.Chapter06;
using OnPopulateMeshBook.TestSupport;
using UnityEngine;

public sealed class TextureQuadGraphicTests
{
    [Test]
    public void Populate_MapsWholeUvRectangle()
    {
        var graphic =
            MeshTestSupport.CreateGraphic<TextureQuadGraphic>(
                new Vector2(120f, 80f));
        var mesh = MeshTestSupport.Build(graphic);
        Assert.That(mesh.uv[0],
            Is.EqualTo(new Vector2(0f, 0f)));
        Assert.That(mesh.uv[1],
            Is.EqualTo(new Vector2(0f, 1f)));
        Assert.That(mesh.uv[2],
            Is.EqualTo(new Vector2(1f, 1f)));
        Assert.That(mesh.uv[3],
            Is.EqualTo(new Vector2(1f, 0f)));
        MeshTestSupport.Destroy(graphic, mesh);
    }

    [Test]
    public void Populate_ZeroAreaProducesEmptyMesh()
    {
        var graphic =
            MeshTestSupport.CreateGraphic<TextureQuadGraphic>(
                Vector2.zero);
        var mesh = MeshTestSupport.Build(graphic);
        Assert.That(mesh.vertexCount, Is.Zero);
        MeshTestSupport.Destroy(graphic, mesh);
    }
}

{
  "fixedInput": "uv=(0,0)..(1,1) checker=4x4",
  "component": "TextureQuadGraphic",
  "vertices": [
    [-210.0, -120.0, 0.0],
    [-210.0, 120.0, 0.0],
    [210.0, 120.0, 0.0],
    [210.0, -120.0, 0.0]
  ],
  "uv": [[0, 0], [0, 1], [1, 1], [1, 0]],
  "colors": [
    [255,255,255,255], [255,255,255,255],
    [255,255,255,255], [255,255,255,255]
  ],
  "indices": [0, 1, 2, 2, 3, 0]
}

"$UNITY_EDITOR" \
  -batchmode -nographics -quit \
  -projectPath "$PROJECT_ROOT/.tmp/unity-onpopulate-mesh-lab" \
  -runTests -testPlatform EditMode \
  -testResults "$ARTIFACTS/editmode-results.xml" \
  -logFile "$ARTIFACTS/editmode.log"

test-run result=Passed
total=19 passed=19 failed=0 skipped=0
duration=0.0400379s

TextureQuadGraphicTests.Populate_MapsWholeUvRectangle
result=Passed
duration=0.000563s
TextureQuadGraphicTests.Populate_ZeroAreaProducesEmptyMesh
result=Passed
duration=0.000105s
process_exit_code=0

// 失败边界：四角重复同一个纹理坐标
var sameUv = new Vector2(0f, 0f);
AddVertex(vh,
    new Vector2(rect.xMin, rect.yMin), sameUv);
AddVertex(vh,
    new Vector2(rect.xMin, rect.yMax), sameUv);
AddVertex(vh,
    new Vector2(rect.xMax, rect.yMax), sameUv);
AddVertex(vh,
    new Vector2(rect.xMax, rect.yMin), sameUv);

failure input:
expected uv=(0,0)..(1,1)

wrong uv:
v0=(0,0)
v1=(0,0)
v2=(0,0)
v3=(0,0)

still valid:
vertexCount=4
indexCount=6
all indices in range

recovery:
restore per-corner uv values in vertex order