我正在寻找一个内置的解决方案来截取已发布的屏幕截图
问题中的 URL 没有隐藏文本。换句话说，一个解决方案
尊重不透明度。
以下代码就是这样做的：尊重 CSS 不透明度。除其他外，它使用Metafile 对象和OleDraw API 来呈现网页的图像。
测试 HTML：
<!DOCTYPE html>
<body style='background-color: grey'>
<div style='background-color: blue; opacity: 0.2; color: yellow'>This is a text</div>
</body>
输出：
代码（控制台应用）：
using Microsoft.Win32;
using System;
using System.ComponentModel;
using System.Drawing;
using System.Drawing.Imaging;
using System.Runtime.InteropServices;
using System.Threading;
using System.Threading.Tasks;
using System.Windows.Forms;
namespace Console_21697048
{
// http://stackoverflow.com/q/21697048/1768303
class Program
{
const string HTML = "<!DOCTYPE html><body style='background-color: grey'><div style='background-color: blue; opacity: 0.2; color: yellow'>This is a text</div></body>";
const string FILE_NAME = "webpage.png";
readonly static Size IMAGE_SIZE = new Size(320, 200);
// Main
static void Main(string[] args)
{
try
{
// enable HTML5 etc (assuming we're running IE9+)
SetFeatureBrowserFeature("FEATURE_BROWSER_EMULATION", 9000);
// force software rendering
SetFeatureBrowserFeature("FEATURE_IVIEWOBJECTDRAW_DMLT9_WITH_GDI", 1);
SetFeatureBrowserFeature("FEATURE_GPU_RENDERING", 0);
using (var apartment = new MessageLoopApartment())
{
// create WebBrowser on a seprate thread with its own message loop
var webBrowser = apartment.Invoke(() => new WebBrowser());
// navigate and wait for the result
apartment.Invoke(() =>
{
var pageLoadedTcs = new TaskCompletionSource<bool>();
webBrowser.DocumentCompleted += (s, e) =>
pageLoadedTcs.TrySetResult(true);
webBrowser.DocumentText = HTML;
return pageLoadedTcs.Task;
}).Wait();
// save the picture
apartment.Invoke(() =>
{
webBrowser.Size = IMAGE_SIZE;
var rectangle = new Rectangle(0, 0, webBrowser.Width, webBrowser.Height);
// get reference DC
using (var screenGraphics = webBrowser.CreateGraphics())
{
var screenHdc = screenGraphics.GetHdc();
// create a metafile
using (var metafile = new Metafile(screenHdc, rectangle, MetafileFrameUnit.Pixel))
{
using (var graphics = Graphics.FromImage(metafile))
{
var hdc = graphics.GetHdc();
var rect = new Rectangle(0, 0, 320, 50);
OleDraw(webBrowser.ActiveXInstance, DVASPECT_CONTENT, hdc, ref rectangle);
graphics.ReleaseHdc(hdc);
}
// save the metafile as bitmap
metafile.Save(FILE_NAME, ImageFormat.Png);
}
screenGraphics.ReleaseHdc(screenHdc);
}
});
// dispose of webBrowser
apartment.Invoke(() => webBrowser.Dispose());
webBrowser = null;
}
}
catch (Exception ex)
{
Console.WriteLine(ex.ToString());
}
}
// interop
const uint DVASPECT_CONTENT = 1;
[DllImport("ole32.dll", PreserveSig = false)]
static extern void OleDraw(
[MarshalAs(UnmanagedType.IUnknown)] object pUnk,
uint dwAspect,
IntPtr hdcDraw,
[In] ref System.Drawing.Rectangle lprcBounds);
// WebBrowser Feature Control
// http://msdn.microsoft.com/en-us/library/ie/ee330733(v=vs.85).aspx
static void SetFeatureBrowserFeature(string feature, uint value)
{
if (LicenseManager.UsageMode != LicenseUsageMode.Runtime)
return;
var appName = System.IO.Path.GetFileName(System.Diagnostics.Process.GetCurrentProcess().MainModule.FileName);
Registry.SetValue(@"HKEY_CURRENT_USER\Software\Microsoft\Internet Explorer\Main\FeatureControl\" + feature,
appName, value, RegistryValueKind.DWord);
}
}
// MessageLoopApartment
// more info: http://stackoverflow.com/a/21808747/1768303
public class MessageLoopApartment : IDisposable
{
Thread _thread; // the STA thread
TaskScheduler _taskScheduler; // the STA thread's task scheduler
public TaskScheduler TaskScheduler { get { return _taskScheduler; } }
/// <summary>MessageLoopApartment constructor</summary>
public MessageLoopApartment()
{
var tcs = new TaskCompletionSource<TaskScheduler>();
// start an STA thread and gets a task scheduler
_thread = new Thread(startArg =>
{
EventHandler idleHandler = null;
idleHandler = (s, e) =>
{
// handle Application.Idle just once
Application.Idle -= idleHandler;
// return the task scheduler
tcs.SetResult(TaskScheduler.FromCurrentSynchronizationContext());
};
// handle Application.Idle just once
// to make sure we're inside the message loop
// and SynchronizationContext has been correctly installed
Application.Idle += idleHandler;
Application.Run();
});
_thread.SetApartmentState(ApartmentState.STA);
_thread.IsBackground = true;
_thread.Start();
_taskScheduler = tcs.Task.Result;
}
/// <summary>shutdown the STA thread</summary>
public void Dispose()
{
if (_taskScheduler != null)
{
var taskScheduler = _taskScheduler;
_taskScheduler = null;
// execute Application.ExitThread() on the STA thread
Task.Factory.StartNew(
() => Application.ExitThread(),
CancellationToken.None,
TaskCreationOptions.None,
taskScheduler).Wait();
_thread.Join();
_thread = null;
}
}
/// <summary>Task.Factory.StartNew wrappers</summary>
public void Invoke(Action action)
{
Task.Factory.StartNew(action,
CancellationToken.None, TaskCreationOptions.None, _taskScheduler).Wait();
}
public TResult Invoke<TResult>(Func<TResult> action)
{
return Task.Factory.StartNew(action,
CancellationToken.None, TaskCreationOptions.None, _taskScheduler).Result;
}
}
}