Use Mesh API to create a radial progress indicator

Version: 2021.3+

This example demonstrates how to use the Mesh API to draw visual content onto a visual element.

Note: The Mesh API is a tool for advanced users. In version 2022.1 and later, if you only want to generate simple geometry, use the Vector API instead. For more information, see Use Vector API to create a radial progress indicator.

Example overview

This example creates a custom control that displays progress, as an alternative to a loading bar. The progress indicator displays a progress value in a partially filled ring around a label that displays the percentage. It supports a value between 0 and 100, which determines how much of the ring is filled.

You can find the completed files that this example creates in this GitHub repository.

先决条件

This guide is for developers familiar with the Unity Editor, UI Toolkit, and C# scripting. Before you start, get familiar with the following:

Create the radial progress indicator and its custom mesh

Create two C# files with one defining the RadialProgress class and another defining the custom mesh. In the C# file that defines the RadialProgress class, create a Factory class to expose the control to UXML and UI Builder.

Create a Unity project with any template.
Create a folder named radial-progress to store your files.

In the radial-progress folder, create a C# scrip named RadialProgress.cs with the following content:

using Unity.Collections;
using UnityEngine;
using UnityEngine.UIElements;

namespace MyUILibrary
{

    // An element that displays progress inside a partially filled circle
    public class RadialProgress : VisualElement
    {
        public new class UxmlTraits : VisualElement.UxmlTraits
        {
            // The progress property is exposed to UXML.
            UxmlFloatAttributeDescription m_ProgressAttribute = new UxmlFloatAttributeDescription()
            {
                name = "progress"
            };

            // Use the Init method to assign the value of the progress UXML attribute to the C# progress property.
            public override void Init(VisualElement ve, IUxmlAttributes bag, CreationContext cc)
            {
                base.Init(ve, bag, cc);

                (ve as RadialProgress).progress = m_ProgressAttribute.GetValueFromBag(bag, cc);
            }
        }

        // Define a factory class to expose this control to UXML.
        public new class UxmlFactory : UxmlFactory<RadialProgress, UxmlTraits> { }

        // These are USS class names for the control overall and the label.
        public static readonly string ussClassName = "radial-progress";
        public static readonly string ussLabelClassName = "radial-progress__label";

        // These objects allow C# code to access custom USS properties.
        static CustomStyleProperty<Color> s_TrackColor = new CustomStyleProperty<Color>("--track-color");
        static CustomStyleProperty<Color> s_ProgressColor = new CustomStyleProperty<Color>("--progress-color");

        // These are the meshes this control uses.
        EllipseMesh m_TrackMesh;
        EllipseMesh m_ProgressMesh;

        // This is the label that displays the percentage.
        Label m_Label;

        // This is the number of outer vertices to generate the circle.
        const int k_NumSteps = 200;

        // This is the number that the Label displays as a percentage.
        float m_Progress;

        // A value between 0 and 100

        public float progress
        {
            // The progress property is exposed in C#.
            get => m_Progress;
            set
            {
                // Whenever the progress property changes, MarkDirtyRepaint() is named. This causes a call to the
                // generateVisualContents callback.
                m_Progress = value;
                m_Label.text = Mathf.Clamp(Mathf.Round(value), 0, 100) + "%";
                MarkDirtyRepaint();
            }
        }

        // This default constructor is RadialProgress's only constructor.
        public RadialProgress()
        {
            // Create a Label, add a USS class name, and add it to this visual tree.
            m_Label = new Label();
            m_Label.AddToClassList(ussLabelClassName);
            Add(m_Label);

            // Create meshes for the track and the progress.
            m_ProgressMesh = new EllipseMesh(k_NumSteps);
            m_TrackMesh = new EllipseMesh(k_NumSteps);

            // Add the USS class name for the overall control.
            AddToClassList(ussClassName);

            // Register a callback after custom style resolution.
            RegisterCallback<CustomStyleResolvedEvent>(evt => CustomStylesResolved(evt));

            // Register a callback to generate the visual content of the control.
            generateVisualContent += context => GenerateVisualContent(context);

            progress = 0.0f;
        }

        static void CustomStylesResolved(CustomStyleResolvedEvent evt)
        {
            RadialProgress element = (RadialProgress)evt.currentTarget;
            element.UpdateCustomStyles();
        }

        // After the custom colors are resolved, this method uses them to color the meshes and (if necessary) repaint
        // the control.
        void UpdateCustomStyles()
        {
            if (customStyle.TryGetValue(s_ProgressColor, out var progressColor))
            {
                m_ProgressMesh.color = progressColor;
            }

            if (customStyle.TryGetValue(s_TrackColor, out var trackColor))
            {
                m_TrackMesh.color = trackColor;
            }

            if (m_ProgressMesh.isDirty || m_TrackMesh.isDirty)
                MarkDirtyRepaint();
        }

        // The GenerateVisualContent() callback method calls DrawMeshes().
        static void GenerateVisualContent(MeshGenerationContext context)
        {
            RadialProgress element = (RadialProgress)context.visualElement;
            element.DrawMeshes(context);
        }

        // DrawMeshes() uses the EllipseMesh utility class to generate an array of vertices and indices, for both the
        // "track" ring (in grey) and the progress ring (in green). It then passes the geometry to the MeshWriteData
        // object, as returned by the MeshGenerationContext.Allocate() method. For the "progress" mesh, only a slice of
        // the index arrays is used to progressively reveal parts of the mesh.
        void DrawMeshes(MeshGenerationContext context)
        {
            float halfWidth = contentRect.width * 0.5f;
            float halfHeight = contentRect.height * 0.5f;

            if (halfWidth < 2.0f || halfHeight < 2.0f)
                return;

            m_ProgressMesh.width = halfWidth;
            m_ProgressMesh.height = halfHeight;
            m_ProgressMesh.borderSize = 10;
            m_ProgressMesh.UpdateMesh();

            m_TrackMesh.width = halfWidth;
            m_TrackMesh.height = halfHeight;
            m_TrackMesh.borderSize = 10;
            m_TrackMesh.UpdateMesh();

            // Draw track mesh first
            var trackMeshWriteData = context.Allocate(m_TrackMesh.vertices.Length, m_TrackMesh.indices.Length);
            trackMeshWriteData.SetAllVertices(m_TrackMesh.vertices);
            trackMeshWriteData.SetAllIndices(m_TrackMesh.indices);

            // Keep progress between 0 and 100
            float clampedProgress = Mathf.Clamp(m_Progress, 0.0f, 100.0f);

            // Determine how many triangles are used to depending on progress, to achieve a partially filled circle
            int sliceSize = Mathf.FloorToInt((k_NumSteps * clampedProgress) / 100.0f);

            if (sliceSize == 0)
                return;

            // Every step is 6 indices in the corresponding array
            sliceSize *= 6;

            var progressMeshWriteData = context.Allocate(m_ProgressMesh.vertices.Length, sliceSize);
            progressMeshWriteData.SetAllVertices(m_ProgressMesh.vertices);

            var tempIndicesArray = new NativeArray<ushort>(m_ProgressMesh.indices, Allocator.Temp);
            progressMeshWriteData.SetAllIndices(tempIndicesArray.Slice(0, sliceSize));
            tempIndicesArray.Dispose();
        }

    }
}

Create a C# script named EllipseMesh.cs with the following content:

using UnityEngine;
using UnityEngine.UIElements;

namespace MyUILibrary
{
    public class EllipseMesh
    {
        int m_NumSteps;
        float m_Width;
        float m_Height;
        Color m_Color;
        float m_BorderSize;
        bool m_IsDirty;
        public Vertex[] vertices { get; private set; }
        public ushort[] indices { get; private set; }

        public EllipseMesh(int numSteps)
        {
            m_NumSteps = numSteps;
            m_IsDirty = true;
        }

        public void UpdateMesh()
        {
            if (!m_IsDirty)
                return;

            int numVertices = numSteps * 2;
            int numIndices = numVertices * 6;

            if (vertices == null || vertices.Length != numVertices)
                vertices = new Vertex[numVertices];

            if (indices == null || indices.Length != numIndices)
                indices = new ushort[numIndices];

            float stepSize = 360.0f / (float)numSteps;
            float angle = -180.0f;

            for (int i = 0; i < numSteps; ++i)
            {
                angle -= stepSize;
                float radians = Mathf.Deg2Rad * angle;

                float outerX = Mathf.Sin(radians) * width;
                float outerY = Mathf.Cos(radians) * height;
                Vertex outerVertex = new Vertex();
                outerVertex.position = new Vector3(width + outerX, height + outerY, Vertex.nearZ);
                outerVertex.tint = color;
                vertices[i * 2] = outerVertex;

                float innerX = Mathf.Sin(radians) * (width - borderSize);
                float innerY = Mathf.Cos(radians) * (height - borderSize);
                Vertex innerVertex = new Vertex();
                innerVertex.position = new Vector3(width + innerX, height + innerY, Vertex.nearZ);
                innerVertex.tint = color;
                vertices[i * 2 + 1] = innerVertex;

                indices[i * 6] = (ushort)((i == 0) ? vertices.Length - 2 : (i - 1) * 2); // previous outer vertex
                indices[i * 6 + 1] = (ushort)(i * 2); // current outer vertex
                indices[i * 6 + 2] = (ushort)(i * 2 + 1); // current inner vertex

                indices[i * 6 + 3] = (ushort)((i == 0) ? vertices.Length - 2 : (i - 1) * 2); // previous outer vertex
                indices[i * 6 + 4] = (ushort)(i * 2 + 1); // current inner vertex
                indices[i * 6 + 5] = (ushort)((i == 0) ? vertices.Length - 1 : (i - 1) * 2 + 1); // previous inner vertex
            }

            m_IsDirty = false;
        }

        public bool isDirty => m_IsDirty;

        void CompareAndWrite(ref float field, float newValue)
        {
            if (Mathf.Abs(field - newValue) > float.Epsilon)
            {
                m_IsDirty = true;
                field = newValue;
            }
        }

        public int numSteps
        {
            get => m_NumSteps;
            set
            {
                m_IsDirty = value != m_NumSteps;
                m_NumSteps = value;
            }
        }

        public float width
        {
            get => m_Width;
            set => CompareAndWrite(ref m_Width, value);
        }

        public float height
        {
            get => m_Height;
            set => CompareAndWrite(ref m_Height, value);
        }

        public Color color
        {
            get => m_Color;
            set
            {
                m_IsDirty = value != m_Color;
                m_Color = value;
            }
        }

        public float borderSize
        {
            get => m_BorderSize;
            set => CompareAndWrite(ref m_BorderSize, value);
        }

    }
}

Use the custom control in a UI Document and test

Create a USS file to style the radial progress indicator custom control. Use UI Builder to add the control and apply the USS stylesheet. Test the control with different Progress values.

Create a USS file named RadialProgress.uss with the following content:

.radial-progress {
    min-width: 26px;
    min-height: 20px;
    --track-color: rgb(130, 130, 130);
    --progress-color: rgb(46, 132, 24);
    --percentage-color: white;
    margin-left: 5px;
    margin-right: 5px;
    margin-top: 5px;
    margin-bottom: 5px;
    flex-direction: row;
    justify-content: center;
    width: 100px; 
    height: 100px;
}

.radial-progress__label {
    -unity-text-align: middle-left;
    color: var(--percentage-color);
}

Create a UI Document named RadialProgressExample.uxml.
Double-click RadialProgressExample.uxml to open it in the UI Builder.
In the Library window, select Project > Custom Controls > MyUILibrary.
Drag RadialProgress to the Hierarchy window.
In the StyleSheets section of the UI Builder, add RadialProgress.uss as existing USS.
In the Hierarchy window, select RadialProgress.
In the Inspector window, enter radial-progress in the Name box.
In the Inspector window, enter different values in the Progress box. The percentage in the Viewport changes, and the green progress ring resizes.

Use the progress indicator in runtime

Use the UI Document in a scene, and create a C# MonoBehaviour script to update the Progress property of the control with dynamic values for demo purposes.

In the radial-progress folder, create a C# script named RadialProgressComponent.cs with the following content:

using System.Collections;
using System.Collections.Generic;
using UnityEngine;
using UnityEngine.UIElements;
using MyUILibrary;

[RequireComponent(typeof(UIDocument))]
public class RadialProgressComponent : MonoBehaviour
{

    RadialProgress m_RadialProgress;

    void Start()
    {
        var root = GetComponent<UIDocument>().rootVisualElement;

        m_RadialProgress = new RadialProgress() {
            style = {
                position = Position.Absolute,
                left = 20, top = 20, width = 200, height = 200
            }
        };

        root.Add(m_RadialProgress);
    }

    void Update()
    {
        // For demo purpose, give the progress property dynamic values.
        m_RadialProgress.progress = ((Mathf.Sin(Time.time) + 1.0f) / 2.0f) * 60.0f + 10.0f;
    }
}

In Unity, select GameObject > UI Toolkit > UI Document.
Select the UIDocument in the Hierarchy window.
Add RadialProgressComponent.cs as a component of the UIDocument GameObject.
Enter play mode. The progress indicator appears in the scene, and the progress ring and value change dynamically.

其他资源

Create custom controls

Use Vector API to create a radial progress indicator

Support for Editor UI