Avalonia/src/Windows/Avalonia.Win32/WindowFramebuffer.cs

using System;
using Avalonia.Platform;
using Avalonia.Win32.Interop;
using PixelFormat = Avalonia.Platform.PixelFormat;

namespace Avalonia.Win32
{
    public class WindowFramebuffer : ILockedFramebuffer
    {
        private readonly IntPtr _handle;
        private IUnmanagedBlob _bitmapBlob;
        private UnmanagedMethods.BITMAPINFOHEADER _bmpInfo;

        public WindowFramebuffer(IntPtr handle, PixelSize size)
        {
            
            if (size.Width <= 0)
                throw new ArgumentException("Width is less than zero");
            if (size.Height <= 0)
                throw new ArgumentException("Height is less than zero");
            _handle = handle;
            _bmpInfo.Init();
            _bmpInfo.biPlanes = 1;
            _bmpInfo.biBitCount = 32;
            _bmpInfo.Init();
            _bmpInfo.biWidth = size.Width;
            _bmpInfo.biHeight = -size.Height;
            _bitmapBlob = AvaloniaLocator.Current.GetService<IRuntimePlatform>().AllocBlob(size.Width * size.Height * 4);
        }

        ~WindowFramebuffer()
        {
            Deallocate();
        }

        public IntPtr Address => _bitmapBlob.Address;
        public int RowBytes => Size.Width * 4;
        public PixelFormat Format => PixelFormat.Bgra8888;

        public Vector Dpi
        {
            get
            {
                if (UnmanagedMethods.ShCoreAvailable)
                {
                    uint dpix, dpiy;

                    var monitor = UnmanagedMethods.MonitorFromWindow(_handle,
                        UnmanagedMethods.MONITOR.MONITOR_DEFAULTTONEAREST);

                    if (UnmanagedMethods.GetDpiForMonitor(
                            monitor,
                            UnmanagedMethods.MONITOR_DPI_TYPE.MDT_EFFECTIVE_DPI,
                            out dpix,
                            out dpiy) == 0)
                    {
                        return new Vector(dpix, dpiy);
                    }
                }
                return new Vector(96, 96);
            }
        }

        public PixelSize Size => new PixelSize(_bmpInfo.biWidth, -_bmpInfo.biHeight);

        public void DrawToDevice(IntPtr hDC, int destX = 0, int destY = 0, int srcX = 0, int srcY = 0, int width = -1,
            int height = -1)
        {
            if (width == -1)
                width = Size.Width;
            if (height == -1)
                height = Size.Height;
            UnmanagedMethods.SetDIBitsToDevice(hDC, destX, destY, (uint) width, (uint) height, srcX, srcY,
                0, (uint)Size.Height, _bitmapBlob.Address, ref _bmpInfo, 0);
        }

        public bool DrawToWindow(IntPtr hWnd, int destX = 0, int destY = 0, int srcX = 0, int srcY = 0, int width = -1,
            int height = -1)
        {
            if (_bitmapBlob.IsDisposed)
                throw new ObjectDisposedException("Framebuffer");
            if (hWnd == IntPtr.Zero)
                return false;
            IntPtr hDC = UnmanagedMethods.GetDC(hWnd);
            if (hDC == IntPtr.Zero)
                return false;
            DrawToDevice(hDC, destX, destY, srcX, srcY, width, height);
            UnmanagedMethods.ReleaseDC(hWnd, hDC);
            return true;
        }

        public void Dispose()
        {
            //It's not an *actual* dispose. This call means "We are done drawing"
            DrawToWindow(_handle);
        }

        public void Deallocate() => _bitmapBlob.Dispose();
    }
}