cursor-lang/CursorLang/Views/LayoutPopupWindow.xaml.cs

using System.Windows;
using System.Windows.Interop;
using CursorLang.Interop;
using CursorLang.Models;
using CursorLang.Services;
using CursorLang.ViewModels;

namespace CursorLang.Views;

/// <summary>
/// The popup with the short name of the layout.
/// Responsible only for showing it, its size and its place on screen: when to take it
/// down is decided by <see cref="Services.LayoutPopupService"/>.
/// </summary>
public partial class LayoutPopupWindow : Window, ILayoutPopupWindow
{
    private readonly AppSettings _settings;
    private Size _contentSize;

    public LayoutPopupWindow(LayoutPopupViewModel viewModel, AppSettings settings)
    {
        InitializeComponent();

        DataContext = viewModel;
        _settings = settings;

        // We create the window in advance to set its bounds before the first show:
        // otherwise it appears at the default size for a moment
        new WindowInteropHelper(this).EnsureHandle();
    }

    /// <summary>
    /// Shows the popup at the place set by the settings.
    /// </summary>
    public void ShowPopup()
    {
        MeasureContent();

        // An already created window is put in place before the show so that it does
        // not flash in its old position; on the very first call there is no handle yet
        ApplyBounds();
        Show();

        // We repeat it after the show: before that the window is subject to the system
        // minimum window size and comes out noticeably larger than its text
        ApplyBounds();
    }

    protected override void OnSourceInitialized(EventArgs e)
    {
        base.OnSourceInitialized(e);

        PopupWindowNative.MakePassive(new WindowInteropHelper(this).Handle);
    }

    // The content size is needed before the show: both the window size and the corner
    // position depend on it. The window has no frame, so the window size equals the
    // content size
    private void MeasureContent()
    {
        var content = (FrameworkElement)Content;
        content.Measure(new Size(double.PositiveInfinity, double.PositiveInfinity));

        _contentSize = content.DesiredSize;
    }

    // Everything is computed in physical pixels: monitors have different scaling,
    // while Window.Left/Top/Width/Height are converted using the DPI of the monitor
    // the window is on right now, which misses the target on a neighbouring monitor
    private void ApplyBounds()
    {
        IntPtr handle = new WindowInteropHelper(this).Handle;
        if (handle == IntPtr.Zero)
        {
            return;
        }

        if (_settings.PlacementMode == PopupPlacementMode.FixedPoint)
        {
            ApplyBoundsOnScreen(handle);
        }
        else
        {
            ApplyBoundsNearAnchor(handle, GetAnchor());
        }
    }

    // The anchor point: the caret in the input field or the mouse cursor. The cursor
    // is a rectangle of zero size, so the corner computation is shared by both
    private PopupWindowNative.Rect GetAnchor()
    {
        if (_settings.PlacementMode == PopupPlacementMode.AtCaret &&
            CaretNative.TryGetCaretRect() is { } caret)
        {
            return caret;
        }

        return PopupLayout.AsAnchor(PopupWindowNative.GetCursorPosition());
    }

    private void ApplyBoundsNearAnchor(IntPtr handle, PopupWindowNative.Rect anchor)
    {
        var anchorPoint = new PopupWindowNative.Point { X = anchor.Left, Y = anchor.Top };
        double scale = PopupWindowNative.GetScaleAt(anchorPoint);

        // Every anchor mode has a side and an offset of its own
        bool atCaret = _settings.PlacementMode == PopupPlacementMode.AtCaret;
        AnchorSide side = atCaret ? _settings.CaretSide : _settings.CursorSide;
        int offset = PopupLayout.ToPixels(atCaret ? _settings.CaretOffset : _settings.CursorOffset, scale);

        int width = PopupLayout.ToPixels(_contentSize.Width, scale);
        int height = PopupLayout.ToPixels(_contentSize.Height, scale);

        PopupWindowNative.Point position = PopupLayout.NearAnchor(anchor, side, offset, width, height);

        PopupWindowNative.SetBounds(handle, position.X, position.Y, width, height);
    }

    private void ApplyBoundsOnScreen(IntPtr handle)
    {
        (PopupWindowNative.Rect work, double scale) = PopupWindowNative.GetActiveMonitorWorkArea();

        int width = PopupLayout.ToPixels(_contentSize.Width, scale);
        int height = PopupLayout.ToPixels(_contentSize.Height, scale);
        int margin = PopupLayout.ToPixels(_settings.ScreenMargin, scale);

        PopupWindowNative.Point position =
            PopupLayout.OnScreen(work, _settings.ScreenPosition, margin, width, height);

        PopupWindowNative.SetBounds(handle, position.X, position.Y, width, height);
    }
}