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HTML to Image in C#（C#实现Html转换为Image，即网页截图）

2012-06-26 13:15 1711 查看

原文链接地址：

http://www.codeproject.com/Articles/58605/HTML-to-Image-in-C

Introduction

In this article, I will show you how to capture an
HTML document as an image using a

WebBrowser

object and the

IViewObject.Draw

method, which according to MSDN draws a representation of an object onto the specified device context. Before we get started, I just want to mention that the obtained results were identical to those obtained using commercial
libraries, so I hope this will be useful to someone.

在这篇文章里，我将会演示如何捕获HTML文档并保存为图片，使用WebBrowser对象和

IViewObject.Draw

方法。

根据MSDN的描述，

IViewObject.Draw

用户将对象的表现画到制定的设备上下文中。

在我们开始之前，。。。

The IViewObject interface

The very first thing that we must do is to define the

IViewObject

interface.

我们必须做的首要事情是，我们需要定义IViewObject接口。

ComVisible(true), ComImport()]
[GuidAttribute("0000010d-0000-0000-C000-000000000046")]
[InterfaceTypeAttribute(ComInterfaceType.InterfaceIsIUnknown)]
public interface IViewObject
{
[return: MarshalAs(UnmanagedType.I4)]
[PreserveSig]
int Draw(
[MarshalAs(UnmanagedType.U4)] UInt32 dwDrawAspect,
int lindex,
IntPtr pvAspect,
[In] IntPtr ptd,
IntPtr hdcTargetDev,
IntPtr hdcDraw,
[MarshalAs(UnmanagedType.Struct)] ref Rectangle lprcBounds,
[MarshalAs(UnmanagedType.Struct)] ref Rectangle lprcWBounds,
IntPtr pfnContinue,
[MarshalAs(UnmanagedType.U4)] UInt32 dwContinue);
[PreserveSig]
int GetColorSet([In, MarshalAs(UnmanagedType.U4)] int dwDrawAspect,
int lindex, IntPtr pvAspect,[In] IntPtr ptd,
IntPtr hicTargetDev, [Out] IntPtr ppColorSet);
[PreserveSig]
int Freeze([In, MarshalAs(UnmanagedType.U4)] int dwDrawAspect,
int lindex, IntPtr pvAspect, [Out] IntPtr pdwFreeze);
[PreserveSig]
int Unfreeze([In, MarshalAs(UnmanagedType.U4)] int dwFreeze);
void SetAdvise([In, MarshalAs(UnmanagedType.U4)] int aspects,
[In, MarshalAs(UnmanagedType.U4)] int advf,
[In, MarshalAs(UnmanagedType.Interface)] IAdviseSink pAdvSink);
void GetAdvise([In, Out, MarshalAs(UnmanagedType.LPArray)] int[] paspects,
[In, Out, MarshalAs(UnmanagedType.LPArray)] int[] advf,
[In, Out, MarshalAs(UnmanagedType.LPArray)] IAdviseSink[] pAdvSink);
}

Below is a summary description of the parameters that the

Draw

method takes (this is the only method we will use):

UInt32 dwDrawAspect

- specifies the aspect to be drawn. Valid values are taken from the

DVASPECT

and

DVASPECT2

enumerations. In this example, I'm using

DVASPECT.CONTENT

so the value passed is 1.

int lindex

- portion of the object that is of interest for the draw operation. Currently, only -1 is supported.

IntPtr pvAspect

- pointer to the additional information.

IntPtr ptd

- describes the device for which the object is to be rendered. We will render for the default target device, so the value passed will be

IntPtr.Zero

IntPtr hdcTargetDev

- information context for the target device indicated by the

ptd

parameter.

IntPtr hdcDraw

- device context on which to draw.

ref Rectangle lprcBounds

- the size of the captured
image.

ref Rectangle lprcWBounds

- the region of the

WebBrowser

object that we want to be captured.

IntPtr pfnContinue

- pointer to a callback function (not used here).

UInt32 dwContinue

- value to pass as a parameter to the function (not used here).

The HtmlCapture class

Now that we have defined our

IViewObject

interface, it is time to move on and create a class that will be used to capture a web page as an
image.

public class HtmlCapture
{
private WebBrowser web;
private Timer tready;
private Rectangle screen;
private Size? imgsize=null;

//an event that triggers when the html document is captured
public delegate void HtmlCaptureEvent(object sender,
Uri url, Bitmap image);
public event HtmlCaptureEvent HtmlImageCapture;

//class constructor
public HtmlCapture()
{
//initialise the webbrowser and the timer
web = new WebBrowser();
tready = new Timer();
tready.Interval = 2000;
screen = Screen.PrimaryScreen.Bounds;
//set the webbrowser width and hight
web.Width = screen.Width;
web.Height = screen.Height;
//suppress script errors and hide scroll bars
web.ScriptErrorsSuppressed = true;
web.ScrollBarsEnabled = false;
//attached events
web.Navigating +=
new WebBrowserNavigatingEventHandler(web_Navigating);
web.DocumentCompleted += newWebBrowserDocumentCompletedEventHandler(web_DocumentCompleted);
tready.Tick += new EventHandler(tready_Tick);
}

#region Public methods
public void Create(string url)
{
imgsize = null;
web.Navigate(url);
}

public void Create(string url,Size imgsz)
{
this.imgsize = imgsz;
web.Navigate(url);
}
#endregion

#region Events
void web_DocumentCompleted(object sender,WebBrowserDocumentCompletedEventArgs e)
{
//start the timer
tready.Start();
}

void web_Navigating(object sender, WebBrowserNavigatingEventArgs e)
{
//stop the timer
tready.Stop();
}

void tready_Tick(object sender, EventArgs e)
{
//stop the timer
tready.Stop();

//capture html as an image
//...
}
#endregion
}

As you can see, I'm using a

Timer

object to determine if the
HTML document is fully loaded and can be captured. The reason I'm doing this is because an
HTML document can trigger the

DocumentCompleted

event multiple times. After the document is fully loaded, the

tready_Tick

method is called.

void tready_Tick(object sender, EventArgs e)
{
//stop the timer
tready.Stop();
//get the size of the document's body
Rectangle body = web.Document.Body.ScrollRectangle;

//check if the document width/height is greater than screen width/height
Rectangle docRectangle = new Rectangle()
{
Location=new Point(0,0),
Size=new Size(body.Width > screen.Width ? body.Width : screen.Width,
body.Height > screen.Height ? body.Height : screen.Height)
};
//set the width and height of the WebBrowser object
web.Width = docRectangle.Width;
web.Height = docRectangle.Height;

//if the imgsize is null, the size of the image will
//be the same as the size of webbrowser object
//otherwise  set the image size to imgsize
Rectangle imgRectangle;
if (imgsize == null)
imgRectangle = docRectangle;
else
imgRectangle = new Rectangle()
{
Location=new Point(0,0),
Size =imgsize.Value
};
//create a bitmap object
Bitmap bitmap = new Bitmap(imgRectangle.Width,imgRectangle.Height);
//get the viewobject of the WebBrowser
IViewObject ivo = web.Document.DomDocument as IViewObject;

using (Graphics g = Graphics.FromImage(bitmap))
{
//get the handle to the device context and draw
IntPtr hdc = g.GetHdc();
ivo.Draw(1, -1, IntPtr.Zero, IntPtr.Zero,
IntPtr.Zero, hdc, ref imgRectangle,
ref docRectangle, IntPtr.Zero, 0);
g.ReleaseHdc(hdc);
}
//invoke the HtmlImageCapture event
HtmlImageCapture(this, web.Url, bitmap);
}

Using the code

HtmlCapture

has an overloaded method named

Create

. If you use the

Create(string url)

method, the size of the
image will be the same as the size of the
HTML document. If you want to create a thumbnail
image of the
HTML document, use

Create(string url,Size imgsz)

private void button2_Click(object sender, EventArgs e)
{
HtmlCapture hc = new HtmlCapture();
hc.HtmlImageCapture +=
new HtmlCapture.HtmlCaptureEvent(hc_HtmlImageCapture);
hc.Create("http://www.codeproject.com");
//or
hc.Create("http://www.codeproject.com",new Size(200,300));
}

void hc_HtmlImageCapture(object sender, Uri url, Bitmap image)
{
image.Save("C:/"+ url.Authority+ ".bmp");
}

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