Avalonia/src/Windows/Avalonia.Direct2D1/SwapChainRenderTarget.cs

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Threading.Tasks;
using Avalonia.Media;
using Avalonia.Platform;
using Avalonia.Win32.Interop;
using SharpDX;
using SharpDX.Direct2D1;
using SharpDX.DXGI;
using PixelFormat = SharpDX.Direct2D1.PixelFormat;
using AlphaMode = SharpDX.Direct2D1.AlphaMode;
using Device = SharpDX.Direct2D1.Device;
using Factory = SharpDX.Direct2D1.Factory;
using Factory2 = SharpDX.DXGI.Factory2;

namespace Avalonia.Direct2D1
{
    public abstract class SwapChainRenderTarget : IRenderTarget
    {
        private Size2 _savedSize;
        private Size2F _savedDpi;
        private DeviceContext _deviceContext;
        private SwapChain1 _swapChain;

        protected SwapChainRenderTarget()
        {
            DxgiDevice = AvaloniaLocator.Current.GetService<SharpDX.DXGI.Device>();
            D2DDevice = AvaloniaLocator.Current.GetService<Device>();
            Direct2DFactory = AvaloniaLocator.Current.GetService<Factory>();
            DirectWriteFactory = AvaloniaLocator.Current.GetService<SharpDX.DirectWrite.Factory>();
        }


        /// <summary>
        /// Gets the Direct2D factory.
        /// </summary>
        public Factory Direct2DFactory
        {
            get;
        }

        /// <summary>
        /// Gets the DirectWrite factory.
        /// </summary>
        public SharpDX.DirectWrite.Factory DirectWriteFactory
        {
            get;
        }

        protected SharpDX.DXGI.Device DxgiDevice { get; }
        
        public Device D2DDevice { get; }

        /// <summary>
        /// Creates a drawing context for a rendering session.
        /// </summary>
        /// <returns>An <see cref="Avalonia.Media.DrawingContext"/>.</returns>
        public DrawingContext CreateDrawingContext()
        {
            var size = GetWindowSize();
            var dpi = GetWindowDpi();

            if (size != _savedSize || dpi != _savedDpi)
            {
                _savedSize = size;
                _savedDpi = dpi;
                CreateSwapChain();
            }

            return new DrawingContext(new Media.DrawingContextImpl(_deviceContext, DirectWriteFactory, _swapChain));
        }

        public void Dispose()
        {
            _deviceContext?.Dispose();
            _swapChain?.Dispose();
        }

        private void CreateSwapChain()
        {
            using (var dxgiAdaptor = DxgiDevice.Adapter)
            using (var dxgiFactory = dxgiAdaptor.GetParent<Factory2>())
            {
                _deviceContext?.Dispose();
                _deviceContext = new DeviceContext(D2DDevice, DeviceContextOptions.None) {DotsPerInch = _savedDpi};


                var swapChainDesc = new SwapChainDescription1
                {
                    Width = _savedSize.Width,
                    Height = _savedSize.Height,
                    Format = Format.B8G8R8A8_UNorm,
                    Stereo = false,
                    SampleDescription = new SampleDescription
                    {
                        Count = 1,
                        Quality = 0,
                    },
                    Usage = Usage.RenderTargetOutput,
                    BufferCount = 2,
                    Scaling = Scaling.None,
                    SwapEffect = SwapEffect.FlipSequential,
                    Flags = 0,
                };

                _swapChain?.Dispose();
                _swapChain = CreateSwapChain(dxgiFactory, swapChainDesc);

                using (var dxgiBackBuffer = _swapChain.GetBackBuffer<Surface>(0))
                using (var d2dBackBuffer = new Bitmap1(
                    _deviceContext,
                    dxgiBackBuffer,
                    new BitmapProperties1(
                        new PixelFormat
                        {
                            AlphaMode = AlphaMode.Ignore,
                            Format = Format.B8G8R8A8_UNorm
                        },
                        _savedDpi.Width,
                        _savedDpi.Height,
                        BitmapOptions.Target | BitmapOptions.CannotDraw)))
                {
                    _deviceContext.Target = d2dBackBuffer;
                }
            }
        }

        protected abstract SwapChain1 CreateSwapChain(Factory2 dxgiFactory, SwapChainDescription1 swapChainDesc);

        protected abstract Size2F GetWindowDpi();

        protected abstract Size2 GetWindowSize();
    }
}