winforms - 带图像的透明 Winform

Question

我有一个 alpha 通道设置为 50% 不透明的图像（PNG 文件）。当我尝试在 TransparencyKey 设置为白色且背景色设置为白色的表单上绘制图像时，我希望图像绘制为 50% 透明。但是，它首先与表单背景色混合，因此它是完全不透明的。有没有办法解决？我不想设置表单的 Opaque 属性，因为表单上的某些图像需要是半透明的，而有些则需要是不透明的。

Answer 1

我最终使用了分层窗口，使用了 WS_EX_LAYERED 扩展窗口样式。

http://msdn.microsoft.com/en-us/library/ms997507.aspx

Answer 2

我不认为你可以。我们有一个启动屏幕，我们在其中做了类似的事情，但我们最终捕获了屏幕并将其设置为表单的背景图像。显然，这似乎只是工作，如果屏幕发生变化，表单的背景不会，事情看起来很奇怪。如果您找到更好的方法，我很想知道。

这是捕获屏幕的代码，只需将 ScreenRect 设置为表单屏幕坐标并调用 Process()：

using System;
using System.Drawing;
using System.Runtime.InteropServices;

namespace TourFactory.Core.Drawing
{
    public class CaptureScreenCommand
    {

        #region Initialization and Destruction

        public CaptureScreenCommand()
        {
        }

        #endregion

        #region Fields and Properties

        // BitBlt is a multipurpose function that takes a ROP (Raster OPeration) code
        // that controls exactly what it does. 0xCC0020 is the ROP code SRCCOPY, i.e.
        // do a simple copy from the source to the destination.
        private const int cRasterOp_SrcCopy = 0xCC0020; // 13369376;

        private Rectangle mScreenRect;
        /// <summary>
        /// Gets or sets the screen coordinates to capture.
        /// </summary>
        public Rectangle ScreenRect
        {
            get { return mScreenRect; }
            set { mScreenRect = value; }
        }

        #endregion

        #region Methods

        public Image Process()
        {
            // use the GDI call and create a DC to the whole display
            var dc1 = CreateDC("DISPLAY", null, 0, 0);
            var g1 = Graphics.FromHdc(dc1);

            // create a compatible bitmap the size of the form
            var bmp = new Bitmap(mScreenRect.Width, mScreenRect.Height, g1);
            var g2 = Graphics.FromImage(bmp);

            // Now go retrace our steps and get the device contexts for both the bitmap and the screen
            // Note: Apparently you have to do this, and can't go directly from the aquired dc or exceptions are thrown
            // when you try to release the dcs
            dc1 = g1.GetHdc();
            var dc2 = g2.GetHdc();

            // Bit Blast the screen into the Bitmap
            BitBlt(dc2, 0, 0, mScreenRect.Width, mScreenRect.Height, dc1, mScreenRect.Left, mScreenRect.Top, cRasterOp_SrcCopy);

            // Remember to release the dc's, otherwise problems down the road
            g1.ReleaseHdc(dc1);
            g2.ReleaseHdc(dc2);

            // return bitmap
            return bmp;
        }

        #endregion

        #region gdi32.dll

        [DllImport("gdi32")]
        private static extern IntPtr CreateDC(string lpDriverName, string lpDeviceName, int lpOutput, int lpInitData);

        [DllImport("gdi32")]
        private static extern bool BitBlt(IntPtr hdcDest, int xDest, int yDest, int width, int height, IntPtr hdcSrc, int xSrc, int ySrc, int dwRop);

        #endregion

    }
}

Answer 3

好的。不要忘记 Vista 有桌面窗口管理器来创建半透明窗口（又名 Areo） http://msdn.microsoft.com/en-us/magazine/cc163435.aspx