I was continuing to play around with IJW. And when I realized that there was no direct Screen Capture method in .NET, I thought I might as well try to make a simple Screen Capturing program. Of course since I knew as much about GDI programming as some of these Canadians seem to know about Cricket, you might as well have guessed that I found things more than a little difficult. Luckily Tom Archer, James Johnson and Neil Van Note promptly answered my questions.
The sample program allows you to capture the entire screen or only the current form and also allows you to save the image, though here I have hard coded the filename and path, as I was too lazy to show a save dialog. If you repeatedly click on the capture buttons, you get a weird effect of cascading screen captures, one on top of the other as shown in the screenshot of the sample program.
Using GetDC or GetWindowDC depending on whether we
are capturing the screen or the current window, we get our HDC
using which we call CreateCompatibleDC to create our memory DC.
Using a call to GetSystemMetrics we get the size of the screen and
then call CreateCompatibleBitmap to create a bitmap. Then we select
this bitmap into the memory DC using a call to SelectObject and
save the old bitmap. Using BitBlt we copy the screen or window
contents into this bitmap which is now selected into the memory DC. Then we
select the original bitmap back into the DC, delete the memory DC, release the
DC, and delete the bitmap. To be frank, there is not much .NET stuff involved in
the code, but imagine if you had to write all this using C#. Think of all the
P/Invoke stuff you'd have to do and the ugly declarations you'd have had to
write for the API calls. With MC++ you are saved all that bother.
The source code is self-explanatory. Notice how I have written my WinMain.
This is because I am including windows.h where WinMain is already prototyped in
that fashion.
#include "stdafx.h"
#using <mscorlib.dll>
#using <System.dll>
#using <System.Drawing.dll>
#using <System.Windows.Forms.dll>
#include <tchar.h>
#include <windows.h>
using namespace System;
using namespace System::ComponentModel;
using namespace System::Drawing;
using namespace System::Windows::Forms;
public __gc class NForm : public Form
{
public:
Button *btn;
Button *btn2;
Button *btn3;
PictureBox *pbox;
void btn_Click(Object *sender, System::EventArgs* e);
void CaptureScreen(bool FullScreen);
NForm()
{
this->StartPosition = FormStartPosition::CenterScreen;
this->Text = "Capture screen - Nish for CodeProject -IJW";
this->Size = Drawing::Size(750,550);
this->FormBorderStyle = System::Windows::Forms::FormBorderStyle::FixedDialog;
btn=new Button();
btn->Text="Capture Screen";
btn->Location=Point(5,5);
btn->Size=Drawing::Size(100,30);
btn->add_Click(new EventHandler(this,&NForm::btn_Click));
this->Controls->Add(btn);
btn2=new Button();
btn2->Text="Capture Form";
btn2->Location=Point(125,5);
btn2->Size=Drawing::Size(100,30);
btn2->add_Click(new EventHandler(this,&NForm::btn_Click));
this->Controls->Add(btn2);
btn3=new Button();
btn3->Text="Save C:\\Z.Jpg";
btn3->Location=Point(250,5);
btn3->Size=Drawing::Size(100,30);
btn3->add_Click(new EventHandler(this,&NForm::btn_Click));
this->Controls->Add(btn3);
pbox = new PictureBox();
pbox->Location=Point(5,45);
pbox->Size=Drawing::Size(730,470);
pbox->BorderStyle = BorderStyle::Fixed3D;
pbox->SizeMode = PictureBoxSizeMode::StretchImage;
this->Controls->Add(pbox);
}
};
int __stdcall WinMain(HINSTANCE,HINSTANCE,LPSTR,int)
{
Application::Run(new NForm());
return 0;
}
void NForm::btn_Click(Object *sender, System::EventArgs *e)
{
if(sender->Equals(btn))
CaptureScreen(true);
else
{
if(sender->Equals(btn2))
CaptureScreen(false);
else
pbox->Image->Save("C:\\Z.Jpg",
Drawing::Imaging::ImageFormat::Jpeg);
}
}
void NForm::CaptureScreen(bool FullScreen)
{
HDC hDC;
if(FullScreen)
hDC = GetDC(NULL); //Get full screen
else
{
HWND hWnd=(HWND)this->Handle.ToInt32(); //Get HWND of form
hDC = GetWindowDC(hWnd); //Now get it's DC handle
}
HDC hMemDC = CreateCompatibleDC(hDC);
RECT r;
GetWindowRect((HWND)this->Handle.ToInt32(),&r); //need this for Form
SIZE size;
if(FullScreen)
{
size.cx = GetSystemMetrics(SM_CXSCREEN);
size.cy = GetSystemMetrics(SM_CYSCREEN);
}
else
{
size.cx = r.right-r.left;
size.cy = r.bottom-r.top;
}
//most of the remaining code is normal GDI stuff
HBITMAP hBitmap = CreateCompatibleBitmap(hDC, size.cx, size.cy);
if (hBitmap)
{
HBITMAP hOld = (HBITMAP) SelectObject(hMemDC, hBitmap);
BitBlt(hMemDC, 0, 0, size.cx, size.cy, hDC, 0, 0, SRCCOPY);
SelectObject(hMemDC, hOld);
DeleteDC(hMemDC);
ReleaseDC(NULL, hDC);
pbox->Image = Image::FromHbitmap(hBitmap);
DeleteObject(hBitmap);
}
}
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hi nish, i found your article very interesting, but following it i encountered a problem o nullreferenceexception probably due tu hdc because at debug you can read that hdc has an undefined value...what am i doing wrong?
Did Nish take all the code from you and post it as an article? 