How to create Trackball in inspector

Questions & Answers
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1

How do I recreate the trackball and slider from the Shadows Midtones Highlights inspector?
image

2

You can start by looking at the source code of the postProcessing stack.

3

Modify this color picker to your own needs:

GIF 08.11.2023 01-37-22

// src*: https://gist.github.com/andrew-raphael-lukasik/e7476208779f70e66fbedf5eb10aa2f8
using UnityEngine;
using UnityEngine.UIElements;

[UnityEngine.Scripting.Preserve]
public class ColorPickerElement : VisualElement
{
    public new class UxmlFactory : UxmlFactory<ColorPickerElement,UxmlTraits> {}
    public new class UxmlTraits : VisualElement.UxmlTraits
    {
        UxmlFloatAttributeDescription hueAttr = new UxmlFloatAttributeDescription{ name="hue" , defaultValue=0.5f };
        UxmlFloatAttributeDescription brightnessAttr = new UxmlFloatAttributeDescription{ name="brightness" , defaultValue=1f };
        public override void Init ( VisualElement ve , IUxmlAttributes attributes , CreationContext context )
        {
            base.Init( ve , attributes , context );
            var instance = (ColorPickerElement) ve;
            instance.hue = hueAttr.GetValueFromBag(attributes,context);
            instance.brightness = brightnessAttr.GetValueFromBag(attributes,context);
        }
    }

    public float hue { get; set; }
    public float brightness { get; set; }

    public Color color => Color.HSVToRGB(1-hue%1,1,brightness);

    public Gradient circleGradient { get; set; } = new Gradient{
        mode = GradientMode.Blend ,
        colorKeys = new GradientColorKey[]{
            new GradientColorKey( Color.HSVToRGB(0,1,1) , 0 ) ,
            new GradientColorKey( Color.HSVToRGB(1*1f/6f,1,1) , 1*1f/6f ) ,
            new GradientColorKey( Color.HSVToRGB(2*1f/6f,1,1) , 2*1f/6f ) ,
            new GradientColorKey( Color.HSVToRGB(3*1f/6f,1,1) , 3*1f/6f ) ,
            new GradientColorKey( Color.HSVToRGB(4*1f/6f,1,1) , 4*1f/6f ) ,
            new GradientColorKey( Color.HSVToRGB(5*1f/6f,1,1) , 5*1f/6f ) ,
            new GradientColorKey( Color.HSVToRGB(1,1,1) , 1 ) ,
        }
    };

    public ColorPickerElement ()
    {
        generateVisualContent += OnGenerateVisualContent;
        this.RegisterCallback<ClickEvent>( OnMouseClicked );
    }

    void OnMouseClicked ( ClickEvent evt )
    {
        Vector2 dir = (Vector2)evt.localPosition - contentRect.center;
        hue = 0.25f + ( Mathf.Atan2(-dir.y,dir.x) / Mathf.PI ) * -0.5f;
        
        Rect rect = contentRect;
        float swh = Mathf.Min( rect.width , rect.height );// smaller dimension
        brightness = dir.magnitude / (swh*0.4f);
        
        this.MarkDirtyRepaint();
    }

    void OnGenerateVisualContent ( MeshGenerationContext mgc )
    {
        Rect rect = contentRect;
        float swh = Mathf.Min( rect.width , rect.height );// smaller dimension
        if( swh<0.01f ) return;// skip rendering when collapsed

        var paint = mgc.painter2D;
        float circleRadius = swh*0.4f;
        float gradientWidth = swh*0.05f;

        // selected color circle
        paint.BeginPath();
        {
            paint.Arc( rect.center , circleRadius-gradientWidth/2 , 0 , 360 );
            paint.fillColor = color;
            paint.Fill();
        }
        paint.ClosePath();

        // color ring
        paint.BeginPath();
        {
            paint.Arc( rect.center , circleRadius , 270-0.001f , -90 , ArcDirection.CounterClockwise );

            paint.lineWidth = gradientWidth + 0.2f;
            paint.strokeColor = Color.black;
            paint.Stroke();// border

            paint.lineWidth = gradientWidth;
            paint.strokeGradient = circleGradient;
            paint.Stroke();// hues
        }
        paint.ClosePath();

        // hue position marker
        paint.BeginPath();
        {
            float hueAngle = -Mathf.PI/2 + hue * Mathf.PI*2;

            paint.Arc( rect.center + Vector2.Scale(new Vector2(circleRadius,circleRadius),new Vector2(Mathf.Cos(hueAngle),Mathf.Sin(hueAngle))) , swh*0.03f , 0 , 360 );
            paint.lineWidth = 0.4f;
            paint.strokeColor = Color.white;
            paint.Stroke();
        }
        paint.ClosePath();
    }

}