Windows窗体：使光标位图部分透明 [英] Windows Forms: Making a cursor bitmap partially transparent

问题描述

我想在拖放操作中使用部分透明的图片。这是所有设置和工作正常，但实际转换到透明度有一个奇怪的副作用。由于某些原因，像素似乎与黑色背景混合。

以下图片描述了此问题：

图a）是原始位图。

图b）是在执行α混合之后产生的内容。显然这比预期的50％alpha滤镜暗得多。

图c）是所需的效果，图像a）具有50％的透明度用绘图程序）。

我用来产生trasparent图像的代码如下：

  Bitmap bmpNew = new Bitmap（bmpOriginal.Width，bmpOriginal.Height）; 
 Graphics g = Graphics.FromImage（bmpNew）; 
 
 //使位图50％透明：
 float [] [] ptsArray = {
 new float [] {1，0，0，0，0} / Red 
 new float [] {0，0，0，0}，// Green 
 new float [] {0，0，1，0，0} $ b new float [] {0，0，0，0.5f，0}，// Alpha 
 new float [] {0，0，0，0，1} //亮度
} 
 ColorMatrix clrMatrix = new ColorMatrix（ptsArray）; 
 ImageAttributes imgAttributes = new ImageAttributes（）; 
 imgAttributes.SetColorMatrix（clrMatrix，ColorMatrixFlag.Default，ColorAdjustType.Bitmap）; 
 g.DrawImage（bmpOriginal，new Rectangle（0，0，bmpOriginal.Width，bmpOriginal.Height），0，0，bmpOriginal.Width，bmpOriginal.Height，GraphicsUnit.Pixel，imgAttributes）; 
 Cursors.Default.Draw（g，new Rectangle（bmpOriginal.Width / 2-8，bmpOriginal.Height / 2  -  8，32，32））; 
 g.Dispose（）; 
 imgAttributes.Dispose（）; 
 return bmpNew; 
  

有人知道为什么Alpha混合不起作用吗？

更新I：

为了清楚起见，如果我在绘制曲面的顶部问题是，我想从现有的图像创建一个完全半透明的图像，并在拖放操作过程中使用它作为一个动态光标。即使跳过上面，只画一个填充的颜色88ffffff矩形产生深灰色。

$ b

更新二：

我已经讨论了很多，并相信这与光标创建有关，我会在下面包括这段代码。如果我GetPixel样本位图刚好在CreateIconIndirect调用之前，四个颜色值似乎是完整的。因此，我有一个感觉，罪魁祸首可能是html5的IconInfo结构的hbmColor或hbmMask成员。

这里是IconInfo结构：

  public struct IconInfo {// http://msdn.microsoft.com/en-us/library/ms648052(VS.85).aspx 
 public bool fIcon; //图标或光标。 True = Icon，False = Cursor 
 public int xHotspot; 
 public int yHotspot; 
 public IntPtr hbmMask; //指定图标位掩码位图。如果这个结构定义了一个黑白图标，
 //这个位掩码被格式化，使得上半部分是图标AND位掩码，而下
 //一半是图标XOR位掩码。在这种情况下，高度应该是2的偶数倍。 
 //如果此结构定义了颜色图标，此掩码仅定义图标的AND位掩码。 
 public IntPtr hbmColor; //处理图标颜色位图。如果此结构定义了一个黑色
 //和白色图标，则此成员可以是可选的。 hbmMask的AND位掩码将SRCAND标志应用于目标; 
 //接下来，通过使用SRCINVERT标志将彩色位图应用（使用XOR）到目标。 
 
} 
  

这里是实际创建Cursor的代码： / p>

  public static Cursor CreateCursor（Bitmap bmp，int xHotSpot，int yHotSpot）{
 IconInfo iconInfo = new IconInfo 
 GetIconInfo（bmp.GetHicon（），ref iconInfo）; 
 iconInfo.hbmColor =（IntPtr）0; 
 iconInfo.hbmMask = bmp.GetHbitmap（）; 
 iconInfo.xHotspot = xHotSpot; 
 iconInfo.yHotspot = yHotSpot; 
 iconInfo.fIcon = false; 
 
 return new Cursor（CreateIconIndirect（ref iconInfo））; 
} 
  

两个外部函数定义如下：

  [DllImport（user32.dll，EntryPoint =CreateIconIndirect）] 
 public static extern IntPtr CreateIconIndirect（ref IconInfo icon）; 
 
 [DllImport（user32.dll）] 
 [return：MarshalAs（UnmanagedType.Bool）] 
 public static extern bool GetIconInfo（IntPtr hIcon，ref IconInfo pIconInfo）; 
  

解决方案

GDI +有许多与alpha混合相关的问题与GDI（和Win32）进行互操作。在这种情况下，调用bmp.GetHbitmap（）会将您的图像与黑色背景混合。关于CodeProject 的文章提供了有关该问题的更多详细信息，以及使用的解决方案

您应该能够使用类似的代码来获取HBITMAP用于掩码：

  [DllImport（kernel32.dll）] 
 public static extern bool RtlMoveMemory（IntPtr dest，IntPtr source，int dwcount） 
 [DllImport（gdi32.dll）] 
 public static extern IntPtr CreateDIBSection（IntPtr hdc，[In，MarshalAs（UnmanagedType.LPStruct）] BITMAPINFO pbmi，uint iUsage，out IntPtr ppvBits，IntPtr hSection， uint dwOffset）; 
 
 public static IntPtr GetBlendedHBitmap（Bitmap bitmap）
 {
 BITMAPINFO bitmapInfo = new BITMAPINFO（）; 
 bitmapInfo.biSize = 40; 
 bmapmapInfo.biBitCount = 32; 
 bitmapInfo.biPlanes = 1; 
 
 bitmapInfo.biWidth = bitmap.Width; 
 bitmapInfo.biHeight = -bitmap.Height; 
 
 IntPtr pixelData; 
 IntPtr hBitmap = CreateDIBSection（
 IntPtr.Zero，bitmapInfo，0，out pixelData，IntPtr.Zero，0）; 
 
 Rectangle bounds = new Rectangle（0，0，bitmap.Width，bitmap.Height）; 
 BitmapData bitmapData = bitmap.LockBits（
 bounds，ImageLockMode.ReadOnly，PixelFormat.Format32bppArgb）; 
 RtlMoveMemory（
 pixelData，bitmapData.Scan0，bitmap.Height * bitmapData.Stride）; 
 
 bitmap.UnlockBits（bitmapData）; 
 return hBitmap; 
} 
  

I want to use partially transparent images in drag/drop operations. This is all set up and works fine, but the actual transformation to transparency has a weird side effect. For some reason, the pixels seem to be blended against a black background.

The following image describes the problem:

Figure a) is the original bitmap.

Figure b) is what is produced after alpha blending has been performed. Obviously this is a lot darker than the intended 50% alpha filter intended.

Figure c) is the desired effect, image a) with 50% transparency (added to the composition with a drawing program).

The code I use to produce the trasparent image is the following:

Bitmap bmpNew = new Bitmap(bmpOriginal.Width, bmpOriginal.Height);
Graphics g = Graphics.FromImage(bmpNew);

// Making the bitmap 50% transparent:
float[][] ptsArray ={ 
    new float[] {1, 0, 0, 0, 0},        // Red
    new float[] {0, 1, 0, 0, 0},        // Green
    new float[] {0, 0, 1, 0, 0},        // Blue
    new float[] {0, 0, 0, 0.5f, 0},     // Alpha
    new float[] {0, 0, 0, 0, 1}         // Brightness
};
ColorMatrix clrMatrix = new ColorMatrix(ptsArray);
ImageAttributes imgAttributes = new ImageAttributes();
imgAttributes.SetColorMatrix(clrMatrix, ColorMatrixFlag.Default, ColorAdjustType.Bitmap);
g.DrawImage(bmpOriginal, new Rectangle(0, 0, bmpOriginal.Width, bmpOriginal.Height), 0, 0, bmpOriginal.Width, bmpOriginal.Height, GraphicsUnit.Pixel, imgAttributes);
Cursors.Default.Draw(g, new Rectangle(bmpOriginal.Width / 2 - 8, bmpOriginal.Height / 2 - 8, 32, 32));
g.Dispose();
imgAttributes.Dispose();
return bmpNew;

Does anyone know why the alpha blending does not work?

Update I:

For clarity, the code does work if I'm alphablending on top of a drawn surface. The problem is that I want to create a completely semitransparent image from an existing image and use this as a dynamic cursor during drag/drop operations. Even skipping the above and only painting a filled rectangle of color 88ffffff yields a dark grey color. Something fishy is going on with the icon.

Update II:

Since I've reseached a whole lot and believe this has got something to do with the Cursor creation, I'm gonna include that code below too. If I GetPixel-sample the bitmap just before the CreateIconIndirect call, the four color values seem to be intact. Thus I have a feeling the culprits might be the hbmColor or the hbmMask members of the IconInfo structure.

Here's the IconInfo structure:

public struct IconInfo {    // http://msdn.microsoft.com/en-us/library/ms648052(VS.85).aspx
    public bool fIcon;      // Icon or cursor. True = Icon, False = Cursor
    public int xHotspot;
    public int yHotspot;
    public IntPtr hbmMask;  // Specifies the icon bitmask bitmap. If this structure defines a black and white icon, 
                            // this bitmask is formatted so that the upper half is the icon AND bitmask and the lower 
                            // half is the icon XOR bitmask. Under this condition, the height should be an even multiple of two. 
                            // If this structure defines a color icon, this mask only defines the AND bitmask of the icon.
    public IntPtr hbmColor; // Handle to the icon color bitmap. This member can be optional if this structure defines a black 
                            // and white icon. The AND bitmask of hbmMask is applied with the SRCAND flag to the destination; 
                            // subsequently, the color bitmap is applied (using XOR) to the destination by using the SRCINVERT flag. 

}

And here is the code that actually creates the Cursor:

    public static Cursor CreateCursor(Bitmap bmp, int xHotSpot, int yHotSpot) {
        IconInfo iconInfo = new IconInfo();
        GetIconInfo(bmp.GetHicon(), ref iconInfo);
        iconInfo.hbmColor = (IntPtr)0;
        iconInfo.hbmMask = bmp.GetHbitmap();
        iconInfo.xHotspot = xHotSpot;
        iconInfo.yHotspot = yHotSpot;
        iconInfo.fIcon = false;

        return new Cursor(CreateIconIndirect(ref iconInfo));
    }

The two external functions are defined as follows:

    [DllImport("user32.dll", EntryPoint = "CreateIconIndirect")]
    public static extern IntPtr CreateIconIndirect(ref IconInfo icon);

    [DllImport("user32.dll")]
    [return: MarshalAs(UnmanagedType.Bool)]
    public static extern bool GetIconInfo(IntPtr hIcon, ref IconInfo pIconInfo);

解决方案

GDI+ has a number of problems related to alpha blending when doing interop with GDI (and Win32). In this case, the call to bmp.GetHbitmap() will blend your image with a black background. An article on CodeProject gives more detail on the problem, and a solution that was used for adding images to an image list.

You should be able to use similar code to get the HBITMAP to use for the mask:

[DllImport("kernel32.dll")]
public static extern bool RtlMoveMemory(IntPtr dest, IntPtr source, int dwcount);
[DllImport("gdi32.dll")]
public static extern IntPtr CreateDIBSection(IntPtr hdc, [In, MarshalAs(UnmanagedType.LPStruct)]BITMAPINFO pbmi, uint iUsage, out IntPtr ppvBits, IntPtr hSection, uint dwOffset);

public static IntPtr GetBlendedHBitmap(Bitmap bitmap)
{
    BITMAPINFO bitmapInfo = new BITMAPINFO();
    bitmapInfo.biSize = 40;
    bitmapInfo.biBitCount = 32;
    bitmapInfo.biPlanes = 1;

    bitmapInfo.biWidth = bitmap.Width;
    bitmapInfo.biHeight = -bitmap.Height;

    IntPtr pixelData;
    IntPtr hBitmap = CreateDIBSection(
        IntPtr.Zero, bitmapInfo, 0, out pixelData, IntPtr.Zero, 0);

    Rectangle bounds = new Rectangle(0, 0, bitmap.Width, bitmap.Height);
    BitmapData bitmapData = bitmap.LockBits(
        bounds, ImageLockMode.ReadOnly, PixelFormat.Format32bppArgb );
    RtlMoveMemory(
        pixelData, bitmapData.Scan0, bitmap.Height * bitmapData.Stride);

    bitmap.UnlockBits(bitmapData);
    return hBitmap;
}

这篇关于Windows窗体：使光标位图部分透明的文章就介绍到这了，希望我们推荐的答案对大家有所帮助，也希望大家多多支持IT屋！