我一直在尝试将透明的PNG图像复制到剪贴板，并保持其透明度将其粘贴到支持它的特定程序中。
我已经尝试了很多解决方案，但背景总是以这种或那种方式变成灰色。
所以我尝试使用Chrome复制相同的图像并将其粘贴到程序中并且有效。它保持了透明度。然后我尝试从剪贴板中获取我使用Chrome复制的图像并再次设置图像，期望透明度仍然存在 - 但是，即使我刚从剪贴板中取出图像并设置它，也不会保留透明度试。
var img = Clipboard.GetImage(); // copied using Chrome and transparency is preserved
Clipboard.SetImage(img); // transparency lost
即使我使用System.Windows.Forms.Clipboard或尝试获取并设置DataObject而不是图片，也会出现同样的问题。
答案 0 :(得分：13)
默认情况下，Windows剪贴板不支持透明度，但您可以将多种类型的内容放在剪贴板上，以确保大多数应用程序在其中找到可以使用的某些类型。可悲的是，最常见的类型（Windows本身似乎使用）是一个非常脏和不可靠的类型。我写了一篇关于here的大 rant 解释。
我会假设你在继续我的答案之前已经阅读过，因为它包含了下一部分所需的背景信息。
现在，将图像放在具有透明度支持的剪贴板上的最简洁方法是PNG流，但不保证所有应用程序都可以粘贴它。 Gimp支持PNG粘贴，显然新的MS Office程序也是如此，但谷歌Chrome不会，并且只接受我链接的答案中详述的凌乱的DIB类型。另一方面，Gimp不会接受DIB具有透明度，因为它的创建者实际上遵循格式的规范，并且意识到格式不可靠（正如我链接的那个问题所清楚地证明的那样）。
由于DIB的混乱，遗憾的是，最好的办法就是尽可能多地将它放在那里，包括PNG，DIB和普通图像。
PNG和DIB都以相同的方式放在剪贴板上：将它们放在DataObject作为MemoryStream，然后在实际打开时给剪贴板“复制”指令。
大部分内容都很简单，但DIB有点复杂。请注意，以下部分包含对我自己的工具集的几个引用。可以找到GetImageData个in this answer，找到BuildImage个here，下面给出ArrayUtils个。
/// <summary>
/// Copies the given image to the clipboard as PNG, DIB and standard Bitmap format.
/// </summary>
/// <param name="image">Image to put on the clipboard.</param>
/// <param name="imageNoTr">Optional specifically nontransparent version of the image to put on the clipboard.</param>
/// <param name="data">Clipboard data object to put the image into. Might already contain other stuff. Leave null to create a new one.</param>
public static void SetClipboardImage(Bitmap image, Bitmap imageNoTr, DataObject data)
{
Clipboard.Clear();
if (data == null)
data = new DataObject();
if (imageNoTr == null)
imageNoTr = image;
using (MemoryStream pngMemStream = new MemoryStream())
using (MemoryStream dibMemStream = new MemoryStream())
{
// As standard bitmap, without transparency support
data.SetData(DataFormats.Bitmap, true, imageNoTr);
// As PNG. Gimp will prefer this over the other two.
image.Save(pngMemStream, ImageFormat.Png);
data.SetData("PNG", false, pngMemStream);
// As DIB. This is (wrongly) accepted as ARGB by many applications.
Byte[] dibData = ConvertToDib(image);
dibMemStream.Write(dibData, 0, dibData.Length);
data.SetData(DataFormats.Dib, false, dibMemStream);
// The 'copy=true' argument means the MemoryStreams can be safely disposed after the operation.
Clipboard.SetDataObject(data, true);
}
}
/// <summary>
/// Converts the image to Device Independent Bitmap format of type BITFIELDS.
/// This is (wrongly) accepted by many applications as containing transparency,
/// so I'm abusing it for that.
/// </summary>
/// <param name="image">Image to convert to DIB</param>
/// <returns>The image converted to DIB, in bytes.</returns>
public static Byte[] ConvertToDib(Image image)
{
Byte[] bm32bData;
Int32 width = image.Width;
Int32 height = image.Height;
// Ensure image is 32bppARGB by painting it on a new 32bppARGB image.
using (Bitmap bm32b = new Bitmap(image.Width, image.Height, PixelFormat.Format32bppArgb))
{
using (Graphics gr = Graphics.FromImage(bm32b))
gr.DrawImage(image, new Rectangle(0, 0, bm32b.Width, bm32b.Height));
// Bitmap format has its lines reversed.
bm32b.RotateFlip(RotateFlipType.Rotate180FlipX);
Int32 stride;
bm32bData = ImageUtils.GetImageData(bm32b, out stride);
}
// BITMAPINFOHEADER struct for DIB.
Int32 hdrSize = 0x28;
Byte[] fullImage = new Byte[hdrSize + 12 + bm32bData.Length];
//Int32 biSize;
ArrayUtils.WriteIntToByteArray(fullImage, 0x00, 4, true, (UInt32)hdrSize);
//Int32 biWidth;
ArrayUtils.WriteIntToByteArray(fullImage, 0x04, 4, true, (UInt32)width);
//Int32 biHeight;
ArrayUtils.WriteIntToByteArray(fullImage, 0x08, 4, true, (UInt32)height);
//Int16 biPlanes;
ArrayUtils.WriteIntToByteArray(fullImage, 0x0C, 2, true, 1);
//Int16 biBitCount;
ArrayUtils.WriteIntToByteArray(fullImage, 0x0E, 2, true, 32);
//BITMAPCOMPRESSION biCompression = BITMAPCOMPRESSION.BITFIELDS;
ArrayUtils.WriteIntToByteArray(fullImage, 0x10, 4, true, 3);
//Int32 biSizeImage;
ArrayUtils.WriteIntToByteArray(fullImage, 0x14, 4, true, (UInt32)bm32bData.Length);
// These are all 0. Since .net clears new arrays, don't bother writing them.
//Int32 biXPelsPerMeter = 0;
//Int32 biYPelsPerMeter = 0;
//Int32 biClrUsed = 0;
//Int32 biClrImportant = 0;
// The aforementioned "BITFIELDS": colour masks applied to the Int32 pixel value to get the R, G and B values.
ArrayUtils.WriteIntToByteArray(fullImage, hdrSize + 0, 4, true, 0x00FF0000);
ArrayUtils.WriteIntToByteArray(fullImage, hdrSize + 4, 4, true, 0x0000FF00);
ArrayUtils.WriteIntToByteArray(fullImage, hdrSize + 8, 4, true, 0x000000FF);
Array.Copy(bm32bData, 0, fullImage, hdrSize + 12, bm32bData.Length);
return fullImage;
}
现在，至于从剪贴板中获取图像，我注意到.Net 3.5与后者之间的行为显然存在差异，这似乎实际上使用了DIB。鉴于这种差异，并且考虑到DIB格式的不可靠性，您需要手动检查所有类型，最好从完全可靠的PNG格式开始。
您可以使用以下代码从剪贴板中获取DataObject：
DataObject retrievedData = Clipboard.GetDataObject() as DataObject;
此处使用的CloneImage函数基本上只是我的GetImageData和BuildImage工具集的组合，确保创建新图像时不会有任何可能混乱的后备资源;已知图像对象在基于Stream的情况下会导致崩溃，然后会被处置掉。已发布here, in a question well worth reading on the subject of why this cloning is so important.
/// <summary>
/// Retrieves an image from the given clipboard data object, in the order PNG, DIB, Bitmap, Image object.
/// </summary>
/// <param name="retrievedData">The clipboard data.</param>
/// <returns>The extracted image, or null if no supported image type was found.</returns>
public static Bitmap GetClipboardImage(DataObject retrievedData)
{
Bitmap clipboardimage = null;
// Order: try PNG, move on to try 32-bit ARGB DIB, then try the normal Bitmap and Image types.
if (retrievedData.GetDataPresent("PNG"))
{
MemoryStream png_stream = retrievedData.GetData("PNG") as MemoryStream;
if (png_stream != null)
using (Bitmap bm = new Bitmap(png_stream))
clipboardimage = ImageUtils.CloneImage(bm);
}
if (clipboardimage == null && retrievedData.GetDataPresent(DataFormats.Dib))
{
MemoryStream dib = retrievedData.GetData(DataFormats.Dib) as MemoryStream;
if (dib != null)
clipboardimage = ImageFromClipboardDib(dib.ToArray());
}
if (clipboardimage == null && retrievedData.GetDataPresent(DataFormats.Bitmap))
clipboardimage = new Bitmap(retrievedData.GetData(DataFormats.Bitmap) as Image);
if (clipboardimage == null && retrievedData.GetDataPresent(typeof(Image)))
clipboardimage = new Bitmap(retrievedData.GetData(typeof(Image)) as Image);
return clipboardimage;
}
public static Bitmap ImageFromClipboardDib(Byte[] dibBytes)
{
if (dibBytes == null || dibBytes.Length < 4)
return null;
try
{
Int32 headerSize = (Int32)ArrayUtils.ReadIntFromByteArray(dibBytes, 0, 4, true);
// Only supporting 40-byte DIB from clipboard
if (headerSize != 40)
return null;
Byte[] header = new Byte[40];
Array.Copy(dibBytes, header, 40);
Int32 imageIndex = headerSize;
Int32 width = (Int32)ArrayUtils.ReadIntFromByteArray(header, 0x04, 4, true);
Int32 height = (Int32)ArrayUtils.ReadIntFromByteArray(header, 0x08, 4, true);
Int16 planes = (Int16)ArrayUtils.ReadIntFromByteArray(header, 0x0C, 2, true);
Int16 bitCount = (Int16)ArrayUtils.ReadIntFromByteArray(header, 0x0E, 2, true);
//Compression: 0 = RGB; 3 = BITFIELDS.
Int32 compression = (Int32)ArrayUtils.ReadIntFromByteArray(header, 0x10, 4, true);
// Not dealing with non-standard formats.
if (planes != 1 || (compression != 0 && compression != 3))
return null;
PixelFormat fmt;
switch (bitCount)
{
case 32:
fmt = PixelFormat.Format32bppRgb;
break;
case 24:
fmt = PixelFormat.Format24bppRgb;
break;
case 16:
fmt = PixelFormat.Format16bppRgb555;
break;
default:
return null;
}
if (compression == 3)
imageIndex += 12;
if (dibBytes.Length < imageIndex)
return null;
Byte[] image = new Byte[dibBytes.Length - imageIndex];
Array.Copy(dibBytes, imageIndex, image, 0, image.Length);
// Classic stride: fit within blocks of 4 bytes.
Int32 stride = (((((bitCount * width) + 7) / 8) + 3) / 4) * 4;
if (compression == 3)
{
UInt32 redMask = ArrayUtils.ReadIntFromByteArray(dibBytes, headerSize + 0, 4, true);
UInt32 greenMask = ArrayUtils.ReadIntFromByteArray(dibBytes, headerSize + 4, 4, true);
UInt32 blueMask = ArrayUtils.ReadIntFromByteArray(dibBytes, headerSize + 8, 4, true);
// Fix for the undocumented use of 32bppARGB disguised as BITFIELDS. Despite lacking an alpha bit field,
// the alpha bytes are still filled in, without any header indication of alpha usage.
// Pure 32-bit RGB: check if a switch to ARGB can be made by checking for non-zero alpha.
// Admitted, this may give a mess if the alpha bits simply aren't cleared, but why the hell wouldn't it use 24bpp then?
if (bitCount == 32 && redMask == 0xFF0000 && greenMask == 0x00FF00 && blueMask == 0x0000FF)
{
// Stride is always a multiple of 4; no need to take it into account for 32bpp.
for (Int32 pix = 3; pix < image.Length; pix += 4)
{
// 0 can mean transparent, but can also mean the alpha isn't filled in, so only check for non-zero alpha,
// which would indicate there is actual data in the alpha bytes.
if (image[pix] == 0)
continue;
fmt = PixelFormat.Format32bppPArgb;
break;
}
}
else
// Could be supported with a system that parses the colour masks,
// but I don't think the clipboard ever uses these anyway.
return null;
}
Bitmap bitmap = ImageUtils.BuildImage(image, width, height, stride, fmt, null, null);
// This is bmp; reverse image lines.
bitmap.RotateFlip(RotateFlipType.Rotate180FlipX);
return bitmap;
}
catch
{
return null;
}
}
由于BitConverter始终要求对系统字节序进行愚蠢检查，因此我在ReadIntFromByteArray类中获得了自己的WriteIntToByteArray和ArrayUtils：
public static void WriteIntToByteArray(Byte[] data, Int32 startIndex, Int32 bytes, Boolean littleEndian, UInt32 value)
{
Int32 lastByte = bytes - 1;
if (data.Length < startIndex + bytes)
throw new ArgumentOutOfRangeException("startIndex", "Data array is too small to write a " + bytes + "-byte value at offset " + startIndex + ".");
for (Int32 index = 0; index < bytes; index++)
{
Int32 offs = startIndex + (littleEndian ? index : lastByte - index);
data[offs] = (Byte)(value >> (8 * index) & 0xFF);
}
}
public static UInt32 ReadIntFromByteArray(Byte[] data, Int32 startIndex, Int32 bytes, Boolean littleEndian)
{
Int32 lastByte = bytes - 1;
if (data.Length < startIndex + bytes)
throw new ArgumentOutOfRangeException("startIndex", "Data array is too small to read a " + bytes + "-byte value at offset " + startIndex + ".");
UInt32 value = 0;
for (Int32 index = 0; index < bytes; index++)
{
Int32 offs = startIndex + (littleEndian ? index : lastByte - index);
value += (UInt32)(data[offs] << (8 * index));
}
return value;
}