AmiReel/Controls/SourceCropEditor.xaml.cs

using System.Runtime.InteropServices.WindowsRuntime;
using AmiReel.Models;
using AmiReel.Services;
using Microsoft.UI.Input;
using Microsoft.UI.Xaml;
using Microsoft.UI.Xaml.Controls;
using Microsoft.UI.Xaml.Input;
using Microsoft.UI.Xaml.Media.Imaging;
using Windows.Foundation;

namespace AmiReel.Controls;

public sealed partial class SourceCropEditor : UserControl
{
    private int _pixelWidth;
    private int _pixelHeight;
    private bool _isDragging;
    private Point _dragStart;
    private PixelInsets _insets;

    public SourceCropEditor()
    {
        InitializeComponent();
    }

    public PixelInsets Insets => _insets;

    public async Task LoadVideoFrameAsync(
        string inputFile, string start, string ffmpegPath, string ffprobePath, CancellationToken token)
    {
        LoadProgress.Visibility = Visibility.Visible;
        StatusText.Text = "Loading a source frame...";
        try
        {
            string directory = Path.Combine(Path.GetTempPath(), "AmiReel", "crop-editor");
            Directory.CreateDirectory(directory);
            string framePath = Path.Combine(directory, "source-frame.png");
            await new ShortsPipeline().ExtractSourceFrameAsync(
                inputFile, start, ffmpegPath, ffprobePath, framePath, _ => { }, token);

            await using FileStream stream = File.OpenRead(framePath);
            BitmapImage bitmap = new();
            await bitmap.SetSourceAsync(stream.AsRandomAccessStream());
            SourceImage.Source = bitmap;
            _pixelWidth = bitmap.PixelWidth;
            _pixelHeight = bitmap.PixelHeight;
            StatusText.Text = $"{_pixelWidth} × {_pixelHeight} · drag on the frame to choose the kept region.";
            RefreshSelectionVisual();
        }
        finally
        {
            LoadProgress.Visibility = Visibility.Collapsed;
        }
    }

    public void SetInsets(PixelInsets insets)
    {
        _insets = insets;
        RefreshSelectionVisual();
        UpdateInsetsText();
    }

    private void CropHost_PointerPressed(object sender, PointerRoutedEventArgs e)
    {
        if (_pixelWidth <= 0 || !TryMapToDisplay(e, out double x, out double y, out _, out _))
            return;

        _isDragging = true;
        _dragStart = new Point(x, y);
        CropHost.CapturePointer(e.Pointer);
        UpdateDraftSelection(x, y);
        e.Handled = true;
    }

    private void CropHost_PointerMoved(object sender, PointerRoutedEventArgs e)
    {
        if (!_isDragging)
            return;
        if (!TryMapToDisplay(e, out double x, out double y, out _, out _))
            return;

        UpdateDraftSelection(x, y);
        e.Handled = true;
    }

    private void CropHost_PointerReleased(object sender, PointerRoutedEventArgs e)
    {
        if (!_isDragging)
            return;

        _isDragging = false;
        CropHost.ReleasePointerCapture(e.Pointer);
        if (TryMapToDisplay(e, out double x, out double y, out double displayWidth, out double displayHeight))
            CommitSelection(x, y, displayWidth, displayHeight);
        e.Handled = true;
    }

    private void CropHost_PointerCaptureLost(object sender, PointerRoutedEventArgs e)
    {
        _isDragging = false;
    }

    private void CropHost_SizeChanged(object sender, SizeChangedEventArgs e) => RefreshSelectionVisual();

    private void ClearCrop_Click(object sender, RoutedEventArgs e) => SetInsets(default);

    private bool TryMapToDisplay(
        PointerRoutedEventArgs e, out double x, out double y, out double displayWidth, out double displayHeight)
    {
        (double offsetX, double offsetY, displayWidth, displayHeight) = CurrentFit();
        x = 0;
        y = 0;
        if (displayWidth <= 0 || displayHeight <= 0)
            return false;

        PointerPoint point = e.GetCurrentPoint(CropHost);
        (x, y) = SourceCropSelection.ClampToDisplay(
            point.Position.X - offsetX, point.Position.Y - offsetY, displayWidth, displayHeight);
        return true;
    }

    private void UpdateDraftSelection(double x, double y)
    {
        (double offsetX, double offsetY, double displayWidth, double displayHeight) = CurrentFit();
        if (displayWidth <= 0)
            return;

        _insets = SourceCropSelection.ToInsets(
            _pixelWidth, _pixelHeight, displayWidth, displayHeight,
            _dragStart.X, _dragStart.Y, x - _dragStart.X, y - _dragStart.Y);
        PlaceSelectionRect(offsetX, offsetY, displayWidth, displayHeight);
        UpdateInsetsText();
    }

    private void CommitSelection(double x, double y, double displayWidth, double displayHeight)
    {
        _insets = SourceCropSelection.ToInsets(
            _pixelWidth, _pixelHeight, displayWidth, displayHeight,
            _dragStart.X, _dragStart.Y, x - _dragStart.X, y - _dragStart.Y);
        RefreshSelectionVisual();
        UpdateInsetsText();
    }

    private void RefreshSelectionVisual()
    {
        (double offsetX, double offsetY, double displayWidth, double displayHeight) = CurrentFit();
        if (displayWidth <= 0 || _pixelWidth <= 0)
        {
            SelectionRect.Visibility = Visibility.Collapsed;
            return;
        }

        PlaceSelectionRect(offsetX, offsetY, displayWidth, displayHeight);
    }

    private void PlaceSelectionRect(double offsetX, double offsetY, double displayWidth, double displayHeight)
    {
        (double x, double y, double width, double height) = SourceCropSelection.ToDisplayRect(
            _pixelWidth, _pixelHeight, displayWidth, displayHeight, _insets);
        Canvas.SetLeft(SelectionRect, offsetX + x);
        Canvas.SetTop(SelectionRect, offsetY + y);
        SelectionRect.Width = width;
        SelectionRect.Height = height;
        SelectionRect.Visibility = _insets.IsEmpty ? Visibility.Collapsed : Visibility.Visible;
    }

    private (double OffsetX, double OffsetY, double DisplayWidth, double DisplayHeight) CurrentFit() =>
        SourceCropSelection.FitUniform(CropHost.ActualWidth, CropHost.ActualHeight, _pixelWidth, _pixelHeight);

    private void UpdateInsetsText() =>
        InsetsText.Text = _pixelWidth <= 0
            ? "Crop L0  R0  T0  B0"
            : $"Crop L{_insets.Left}  R{_insets.Right}  T{_insets.Top}  B{_insets.Bottom}  ·  {_pixelWidth - _insets.Left - _insets.Right}×{_pixelHeight - _insets.Top - _insets.Bottom}";
}