BeatWidget/BsWidget/BaseForm.cs

using System;
using System.Diagnostics;
using System.Drawing;
using System.Drawing.Imaging;
using System.Runtime.InteropServices;
using System.Windows.Forms;

// ReSharper disable UnusedMember.Local
// ReSharper disable IdentifierTypo
// ReSharper disable MemberCanBePrivate.Global

namespace BsWidget
{
    public abstract partial class BaseForm : Form
    {
        private const int WM_NCLBUTTONDOWN = 0xA1;
        private const int HT_CAPTION = 0x2;
        private const int WS_EX_LAYERED = 0x00080000;
        public const byte AcSrcOver = 0x00;
        public const byte AcSrcAlpha = 0x01;
        public const int UlwAlpha = 0x00000002;

        [StructLayout(LayoutKind.Sequential)]
        public struct POINT
        {
            public int x;
            public int y;

            public POINT(int x, int y)
            {
                this.x = x;
                this.y = y;
            }
        }

        [StructLayout(LayoutKind.Sequential)]
        public struct SIZE
        {
            public int cx;
            public int cy;

            public SIZE(int cx, int cy)
            {
                this.cx = cx;
                this.cy = cy;
            }
        }

        [StructLayout(LayoutKind.Sequential, Pack = 1)]
        public struct Blendfunction
        {
            public byte BlendOp;
            public byte BlendFlags;
            public byte SourceConstantAlpha;
            public byte AlphaFormat;
        }

        [DllImport("user32", ExactSpelling = true, SetLastError = true)]
        public static extern bool UpdateLayeredWindow(IntPtr hwnd, IntPtr hdcDst, ref POINT pptDst, ref SIZE psize,
            IntPtr hdcSrc, ref POINT pprSrc, int crKey, ref Blendfunction pblend, int dwFlags);

        [DllImport("user32", ExactSpelling = true, SetLastError = true)]
        public static extern IntPtr GetDC(IntPtr hWnd);

        [DllImport("user32", ExactSpelling = true)]
        public static extern int ReleaseDC(IntPtr hWnd, IntPtr hDc);

        [DllImport("gdi32", ExactSpelling = true, SetLastError = true)]
        public static extern IntPtr CreateCompatibleDC(IntPtr hDc);

        [DllImport("gdi32", ExactSpelling = true, SetLastError = true)]
        public static extern bool DeleteDC(IntPtr hdc);

        [DllImport("gdi32", ExactSpelling = true)]
        public static extern IntPtr SelectObject(IntPtr hDc, IntPtr hObject);

        [DllImport("gdi32", ExactSpelling = true, SetLastError = true)]
        public static extern bool DeleteObject(IntPtr hObject);

        private Size _viewSize;
        private Bitmap _buffedBitmap;

        public BaseForm() => InitializeComponent();

        protected override CreateParams CreateParams
        {
            get
            {
                var cp = base.CreateParams;
                cp.ExStyle |= WS_EX_LAYERED;
                return cp;
            }
        }

        protected override void OnSizeChanged(EventArgs e)
        {
            _viewSize = Size;
            base.OnSizeChanged(e);

            var old = _buffedBitmap;
            var sz = ViewSize;
            _buffedBitmap = new Bitmap(sz.Width, sz.Height, PixelFormat.Format32bppArgb);
            UpdateGraphic();
            old?.Dispose();
        }

        public Size ViewSize
        {
            get { return _viewSize; }
            protected set
            {
                if (value.Width > 0 && value.Height > 0)
                {
                    MinimumSize = value;
                    MaximumSize = value;
                    _viewSize = value;
                }
            }
        }

        protected void UpdateGraphic()
        {
            if (_buffedBitmap == null) return;

            using (var g = Graphics.FromImage(_buffedBitmap))
            {
                RenderGraphic(g);
            }

            var screenDc = GetDC(IntPtr.Zero);
            var memDc = CreateCompatibleDC(screenDc);
            var hBitmap = IntPtr.Zero;
            var oldBitmap = IntPtr.Zero;

            try
            {
                hBitmap = _buffedBitmap.GetHbitmap(Color.FromArgb(0)); // 创建GDI位图句柄，效率较低
                oldBitmap = SelectObject(memDc, hBitmap);

                var topPos = new POINT(Left, Top);
                var pointSource = new POINT(0, 0);
                var size = new SIZE(_buffedBitmap.Width, _buffedBitmap.Height);
                var blend = new Blendfunction
                {
                    BlendOp = AcSrcOver,
                    BlendFlags = 0,
                    SourceConstantAlpha = 255,
                    AlphaFormat = AcSrcAlpha
                };

                UpdateLayeredWindow(
                    Handle, screenDc
                    , ref topPos, ref size
                    , memDc, ref pointSource
                    , 0, ref blend,
                    UlwAlpha);
            }
            catch (Exception ex)
            {
                Debug.Print(ex.ToString());
            }
            finally
            {
                SelectObject(memDc, oldBitmap);
                DeleteObject(hBitmap);
                DeleteObject(oldBitmap);
                ReleaseDC(IntPtr.Zero, screenDc);
                DeleteDC(screenDc);
                DeleteDC(memDc);
            }
        }

        protected abstract void RenderGraphic(Graphics g);
    }
}