本文探讨了在Windows环境中应用程序绘图超出其窗口客户区的问题。通常情况下，使用BeginPaint或GetDC函数获取设备上下文时，绘图会被限制在客户区内。然而，通过GetWindowDC或CreateDC函数，应用程序可以绘制到非客户区甚至整个显示区域。
INFO: Drawing Outside a Window's Client Area
SUMMARY
When an application uses the BeginPaint or GetDC function to obtain a device context (DC) for its client window and draws into this DC, Windows clips the output to the edge of the client window. While this is usually the desired effect, there are circumstances where an application draws outside the client area of its window.
MORE INFORMATION
The GetWindowDC function provides a DC that allows an application to draw anywhere within its window, including the nonclient area.
In the Windows environment, the display is a scarce resource that is shared by all applications running in the system. Most of the time, an application should restrict its output to the area of the screen it has been assigned by the user. However, an application can use the CreateDC function to obtain a DC for the entire display, as follows: hDC = CreateDC("DISPLAY", NULL, NULL, NULL);
Device contexts are another scarce resource in the Windows environment. When an application creates a DC in response to a WM_PAINT message, it must call the DeleteDC function to free the DC before it completes processing of the message.
Painting in the nonclient area of a window is not recommended. If an application changes the nonclient area of its window, the user can become confused because the familiar Windows controls change appearance or are not available. An application should not corrupt other windows on the display.
SUMMARY
When an application uses the BeginPaint or GetDC function to obtain a device context (DC) for its client window and draws into this DC, Windows clips the output to the edge of the client window. While this is usually the desired effect, there are circumstances where an application draws outside the client area of its window.
MORE INFORMATION
The GetWindowDC function provides a DC that allows an application to draw anywhere within its window, including the nonclient area.
In the Windows environment, the display is a scarce resource that is shared by all applications running in the system. Most of the time, an application should restrict its output to the area of the screen it has been assigned by the user. However, an application can use the CreateDC function to obtain a DC for the entire display, as follows: hDC = CreateDC("DISPLAY", NULL, NULL, NULL);
Device contexts are another scarce resource in the Windows environment. When an application creates a DC in response to a WM_PAINT message, it must call the DeleteDC function to free the DC before it completes processing of the message.
Painting in the nonclient area of a window is not recommended. If an application changes the nonclient area of its window, the user can become confused because the familiar Windows controls change appearance or are not available. An application should not corrupt other windows on the display.
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