VisualElement.generateVisualContent

描述

用于生成可视元素的可视内容的委托函数。

使用此委托在 VisualElement 的内容区域中生成自定义几何图形。

此委托在 VisualElement 的初始创建期间以及每次需要重绘时调用。此委托并非在每一帧刷新时都调用。要强制重绘，请调用 VisualElement.MarkDirtyRepaint。

注意：当您在处理程序中执行代码以调用此委托时，请勿更新 VisualElement 的任何属性，因为这可能会更改生成的内容并导致意外的副作用，例如延迟或更新丢失。为避免这种情况，请在委托内将 VisualElement 视为只读。

其他资源：MeshGenerationContext

//This example creates a custom element that dynamically renders a textured rectangle 
//based on the element’s size. 

using UnityEngine;
using UnityEngine.UIElements;

public class TexturedElement : VisualElement
{
    static readonly Vertex[] k_Vertices = new Vertex[4];
    static readonly ushort[] k_Indices = { 0, 1, 2, 2, 3, 0 };

    static TexturedElement()
    {
        k_Vertices[0].tint = Color.white;
        k_Vertices[1].tint = Color.white;
        k_Vertices[2].tint = Color.white;
        k_Vertices[3].tint = Color.white;

        k_Vertices[0].uv = new Vector2(0, 0);
        k_Vertices[1].uv = new Vector2(0, 1);
        k_Vertices[2].uv = new Vector2(1, 1);
        k_Vertices[3].uv = new Vector2(1, 0);
    }

    Texture2D m_Texture;

    public TexturedElement()
    {
        //This element grows to fill the available space.
        style.flexGrow = 1.0f;
        
        //Subscribes the OnGenerateVisualContent method to the generateVisualContent delegate.
        generateVisualContent += OnGenerateVisualContent;

        //Create a simple 2x2 checkerboard texture.
        m_Texture = new Texture2D(2, 2);
        m_Texture.SetPixels(new Color[] {
            Color.white, Color.black,
            Color.black, Color.white
        });
        m_Texture.Apply();

        //You can also load a texture from a file.
        //m_Texture = AssetDatabase.LoadAssetAtPath<Texture2D>("Assets/tex.png");
    }

    //This method is called when the element needs to render its content.
    void OnGenerateVisualContent(MeshGenerationContext mgc)
    {
        Rect r = contentRect;
        if (r.width < 0.01f || r.height < 0.01f)
            return; // Skip rendering when too small.

        float left = 0;
        float right = r.width;
        float top = 0;
        float bottom = r.height;

        k_Vertices[0].position = new Vector3(left, bottom, Vertex.nearZ);
        k_Vertices[1].position = new Vector3(left, top, Vertex.nearZ);
        k_Vertices[2].position = new Vector3(right, top, Vertex.nearZ);
        k_Vertices[3].position = new Vector3(right, bottom, Vertex.nearZ);

        MeshWriteData mwd = mgc.Allocate(k_Vertices.Length, k_Indices.Length, m_Texture);

        mwd.SetAllVertices(k_Vertices);
        mwd.SetAllIndices(k_Indices);
    }
}