从剪贴板复制到剪贴板会丢失图像透明度
Copying From and To Clipboard loses image transparency
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以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结束。
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成功了。它保留了透明度。因此，我尝试从使用 Chrome 复制的剪贴板中获取图像并再次设置图像，希望透明度仍然存在 - 但不，即使我只是从中获取图像，透明度也没有保留剪贴板并重新设置它。
var img = Clipboard.GetImage(); // copied using Chrome and transparency is preserved
Clipboard.SetImage(img); // transparency lost
同样的问题，即使我使用 System.Windows.Forms.Clipboard 或尝试获取和设置 DataObject 而不是图像。
Windows剪贴板默认不支持透明，但您可以将剪贴板上的内容以多种类型放在一起，以确保大多数应用程序都能在其中找到可以使用的类型。可悲的是，最常见的类型 DeviceIndependentBitmap（Windows 本身似乎使用）是一种非常肮脏且不可靠的类型。我写了一个很大的 rant 解释 .
我假设您在继续我的回答之前已经通读了这篇文章，因为它包含了下一部分所需的背景信息。
现在，将支持透明度的图像放入剪贴板的最简洁方法是 PNG 流，但它不能保证所有应用程序都可以粘贴它。 Gimp 支持 PNG 粘贴，显然较新的 MS Office 程序也是如此，但是 Google Chrome 不支持，并且只接受我链接到的答案中详述的混乱 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了格式的规范，并意识到格式是不可靠的（正如我链接的那个问题清楚地证明的那样）。
由于 DIB 乱七八糟，遗憾的是，最好的办法就是将它放入尽可能多的普遍支持的类型中，包括 PNG、DIB 和普通图像。
PNG和DIB放入剪贴板的方式相同：将它们放入DataObject作为MemoryStream，然后在实际放入时给剪贴板“复制”指令上。
大部分都很简单，但 DIB 有点复杂。请注意，以下部分包含对我自己的工具集的一些引用。 GetImageData 的可以在 in this answer, the BuildImage one can be found here 中找到，ArrayUtils 的在下面给出。
不过，这些工具集都使用 System.Drawing。您必须自己弄清楚如何在 WPF 中做同样的事情。
/// <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，关于从剪贴板中获取图像，我注意到 .Net 3.5 和更高版本之间的行为明显不同，后者似乎实际上使用了该 DIB。考虑到这种差异，并考虑到 DIB 格式的不可靠性，您需要实际手动检查所有类型，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;
这里使用的 CloneImage 函数基本上只是我的 GetImageData 和 BuildImage 工具集的组合，确保创建新图像时没有任何可能混乱的后备资源；众所周知，图像对象基于 Stream 然后被处置时会导致崩溃。它的压缩和优化版本已发布 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", false))
{
MemoryStream png_stream = retrievedData.GetData("PNG", false) as MemoryStream;
if (png_stream != null)
using (Bitmap bm = new Bitmap(png_stream))
clipboardimage = ImageUtils.CloneImage(bm);
}
if (clipboardimage == null && retrievedData.GetDataPresent(DataFormats.Dib, false))
{
MemoryStream dib = retrievedData.GetData(DataFormats.Dib, false) 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;
}
}
因为 BitConverter 总是需要对系统字节顺序进行愚蠢的检查，所以我在 ArrayUtils class 中得到了自己的 ReadIntFromByteArray 和 WriteIntToByteArray:
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;
}
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以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结束。
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成功了。它保留了透明度。因此，我尝试从使用 Chrome 复制的剪贴板中获取图像并再次设置图像，希望透明度仍然存在 - 但不，即使我只是从中获取图像，透明度也没有保留剪贴板并重新设置它。
var img = Clipboard.GetImage(); // copied using Chrome and transparency is preserved
Clipboard.SetImage(img); // transparency lost
同样的问题，即使我使用 System.Windows.Forms.Clipboard 或尝试获取和设置 DataObject 而不是图像。
Windows剪贴板默认不支持透明，但您可以将剪贴板上的内容以多种类型放在一起，以确保大多数应用程序都能在其中找到可以使用的类型。可悲的是，最常见的类型 DeviceIndependentBitmap（Windows 本身似乎使用）是一种非常肮脏且不可靠的类型。我写了一个很大的 rant 解释
我假设您在继续我的回答之前已经通读了这篇文章，因为它包含了下一部分所需的背景信息。
现在，将支持透明度的图像放入剪贴板的最简洁方法是 PNG 流，但它不能保证所有应用程序都可以粘贴它。 Gimp 支持 PNG 粘贴，显然较新的 MS Office 程序也是如此，但是 Google Chrome 不支持，并且只接受我链接到的答案中详述的混乱 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了格式的规范，并意识到格式是不可靠的（正如我链接的那个问题清楚地证明的那样）。
由于 DIB 乱七八糟，遗憾的是，最好的办法就是将它放入尽可能多的普遍支持的类型中，包括 PNG、DIB 和普通图像。
PNG和DIB放入剪贴板的方式相同：将它们放入DataObject作为MemoryStream，然后在实际放入时给剪贴板“复制”指令上。
大部分都很简单，但 DIB 有点复杂。请注意，以下部分包含对我自己的工具集的一些引用。 GetImageData 的可以在 in this answer, the BuildImage one can be found here 中找到，ArrayUtils 的在下面给出。
不过，这些工具集都使用 System.Drawing。您必须自己弄清楚如何在 WPF 中做同样的事情。
/// <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，关于从剪贴板中获取图像，我注意到 .Net 3.5 和更高版本之间的行为明显不同，后者似乎实际上使用了该 DIB。考虑到这种差异，并考虑到 DIB 格式的不可靠性，您需要实际手动检查所有类型，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;
这里使用的 CloneImage 函数基本上只是我的 GetImageData 和 BuildImage 工具集的组合，确保创建新图像时没有任何可能混乱的后备资源；众所周知，图像对象基于 Stream 然后被处置时会导致崩溃。它的压缩和优化版本已发布 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", false))
{
MemoryStream png_stream = retrievedData.GetData("PNG", false) as MemoryStream;
if (png_stream != null)
using (Bitmap bm = new Bitmap(png_stream))
clipboardimage = ImageUtils.CloneImage(bm);
}
if (clipboardimage == null && retrievedData.GetDataPresent(DataFormats.Dib, false))
{
MemoryStream dib = retrievedData.GetData(DataFormats.Dib, false) 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;
}
}
因为 BitConverter 总是需要对系统字节顺序进行愚蠢的检查，所以我在 ArrayUtils class 中得到了自己的 ReadIntFromByteArray 和 WriteIntToByteArray:
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;
}