QuestPDF/QuestPDF.Previewer/PreviewerControl.cs

using System.Collections.ObjectModel;
using System.Diagnostics;
using System.Reactive.Linq;
using System.Runtime.InteropServices.ComTypes;
using Avalonia;
using Avalonia.Controls;
using Avalonia.Controls.Presenters;
using Avalonia.Input;
using Avalonia.Interactivity;
using Avalonia.Media;

namespace QuestPDF.Previewer
{
    internal class PreviewerControl : Control
    {
        public static readonly StyledProperty<ObservableCollection<RenderedPageInfo>?> PagesProperty =
            AvaloniaProperty.Register<PreviewerControl, ObservableCollection<RenderedPageInfo>>(nameof(Pages));

        private InteractiveCanvas InteractiveCanvas { get; set; } = new InteractiveCanvas();
        
        public ObservableCollection<RenderedPageInfo>? Pages
        {
            get => GetValue(PagesProperty);
            set => SetValue(PagesProperty, value);
        }

        public PreviewerControl()
        {
            PagesProperty.Changed.Subscribe(p =>
            {
                InteractiveCanvas.Pages = Pages;
                InvalidateVisual();
            });

            ClipToBounds = true;
        }
        
        protected override void OnPointerWheelChanged(PointerWheelEventArgs e)
        {
            base.OnPointerWheelChanged(e);

            if ((e.KeyModifiers & KeyModifiers.Control) != 0)
            {
                var scaleFactor = 1 + e.Delta.Y / 10f;
                var point = Bounds.Center - Bounds.TopLeft - e.GetPosition(this);
                
                InteractiveCanvas.ZoomToPoint((float)point.X, (float)point.Y, (float)scaleFactor);
            }
                
            if (e.KeyModifiers == KeyModifiers.None)
            {
                var translation = (float)e.Delta.Y * 25;
                InteractiveCanvas.TranslateWithCurrentScale(0, translation);
            }
                
            InvalidateVisual();
        }

        private bool IsMousePressed { get; set; }
        private Vector MousePosition { get; set; }
        
        protected override void OnPointerMoved(PointerEventArgs e)
        {
            base.OnPointerMoved(e);

            if (IsMousePressed)
            {
                var currentPosition = e.GetPosition(this);
                var translation = currentPosition - MousePosition;
                InteractiveCanvas.TranslateWithCurrentScale((float)translation.X, (float)translation.Y);
                
                InvalidateVisual();
            }

            MousePosition = e.GetPosition(this);
        }
        
        protected override void OnPointerPressed(PointerPressedEventArgs e)
        {
            base.OnPointerPressed(e);
            IsMousePressed = true;
        }

        protected override void OnPointerReleased(PointerReleasedEventArgs e)
        {
            base.OnPointerReleased(e);
            IsMousePressed = false;
        }

        public override void Render(DrawingContext context)
        {
            InteractiveCanvas.Bounds = new Rect(0, 0, Bounds.Width, Bounds.Height);

            context.Custom(InteractiveCanvas);
            base.Render(context);
        }
    }
}