s&box

Panels/UITests/Basics/MouseCapture.razor
@using Sandbox
@using Sandbox.UI
@namespace Sandbox.UI.Tests.Basics
@inherits PanelComponent

<root>

    <BaseTestPanel Title="Mouse Capture Tests" subtitle="Tests for capturing the mouse">
        <Body>
            <label @ref="label">Click on bg</label>
        </Body>
    </BaseTestPanel>

</root>

@code
{
    Label label;
    Vector2 position;

    protected override void OnUpdate()
    {
        if (Panel.HasMouseCapture)
        {
            position += Mouse.Delta;

            label.Text = $"{position.x}\n{position.y}";

            label.Style.Left = position.x;
            label.Style.Top = position.y;
            label.Style.Dirty();

            // When the mouse becomes visible again,
            // we'll put the cursor in the middle of this box
            Mouse.Position = label.Box.Rect.Position + label.Box.Rect.Size * 0.5f;
        }
    }

    protected override void OnMouseDown(MousePanelEvent e)
    {
        e.StopPropagation();

        Panel.SetMouseCapture(true);
    }

    protected override void OnMouseUp(MousePanelEvent e)
    {
        if ( e.Button == "mouseleft" )
        {
            Panel.SetMouseCapture(false);
        }
    }
}