Screen Capturing via GDI+ and GDI - Adding a Reference to GDI and Visualizing the Result
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VC++ is different from VC# (which provides built-in support for GDI+). A VC++ based project has to first add a proper reference to the GDI+ library in order to leverage all the functions in GDI+. In this case, we should consider the following steps:
(1) Open the head file stdafx.h and append the three lines below to the end of it:
#include <gdiplus.h>
#pragma comment(lib, "gdiplus.lib")
using namespace Gdiplus;
(2) Define a variable member for the CscreenCaptureApp class as follows:
ULONG_PTR m_gdiplusToken;
(3) Initialize the GDI+ library within the InitInstance() method of the CscreenCaptureApp class before using it:
Gdiplus::GdiplusStartupInput gdiplusStartupInput;
Gdiplus::GdiplusStartup(&m_gdiplusToken, &gdiplusStartupInput, NULL);
(4) Perform the necessary cleanup within the ExitInstance() method of the CscreenCaptureApp class with the related info used in GDI+:
Gdiplus::GdiplusShutdown(m_gdiplusToken);
Now, with everything ready you can leverage all the above functions provided in GDI+. Let’s start the demo application and see what happens. Press F5 to launch the application. You will see a common dialog, as is shown in Figure 1.
Figure 1— the initial running-time snapshot of the screen capturing application
Just press the left button of the mouse and try to drag; there will be a red rectangle appearing around the window the current cursor points to. When the user releases the left button, the image of the present window will be copied into the system clipboard and a dialog will appear to prompt you to specify the path to persist the image. Figure 2 gives a running-time snapshot when the mouse moves over the window of the FireFox browser.
Figure 2—move the mouse cursor and capture some window in the red rectangle
Because of the shortage of the tool I used to capture the screenshot, it seems the camera shaped mouse cursor is not in Figure 2. Never mind—you can surely catch sight of it in the real sample application.
Summary
In this article, we examined the core module of a screen capture application under Windows via GDI and GDI+. Readers should now have a clearer understanding when composing graphic applications.
On the other hand, GDI+ is expected to become the new graphic engine for the next generation.
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