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ReleaseDC.md

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Function name : ReleaseDC

Group: Device Context - Library: user32

The ReleaseDC function releases a device context (DC), freeing it for use by other applications. For memory device contexts use the DeleteDC function.

Code examples:

How to view icons stored in executable files (Icon Viewer) - II
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Creating a clipping region from the path selected into the device context of a form
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Storing screen shot of a form to bitmap file
Retrieving graphic capabilities of your display
Storing content of the Clipboard to a bitmap file
Drawing icons associated with the VFP main window
Drawing cursors for the classes defined by the system (preregistered): BUTTON, EDIT, LISTBOX etc.
Using the LoadImage function to have a bitmap file loaded and displayed on VFP main window
How to print a bitmap file
Obtaining the bounding rectangle for the specified device context
Drawing a window caption using the DrawCaption routine
Drawing Windows predefined bitmaps using the LoadBitmap functions
Drawing Windows frame controls using the DrawFrameControl function
Drawing a rectangle using Windows regular edges and borders
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Reading metrics for the currently selected font
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How to make a VFP form fading out when released (GDI version)
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GDI+: Scrolling through large image using the mouse
GDI+: Creating thumbnails to preview images in a directory
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GDI+: Color Transparency
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GDI+: Implementing image scrolling with inertia
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Declaration:

int ReleaseDC(
    HWND  hwnd,	// handle of window
    HDC  hdc 	// handle of device context
   );

FoxPro declaration:

DECLARE INTEGER ReleaseDC IN user32;
	INTEGER hwnd,;
	INTEGER hdc

Parameters:

hwnd Identifies the window whose device context is to be released

hdc Identifies the device context to be released

Return value:

The return value specifies whether the device context is released. If the device context is released, the return value is 1

Comments:

Once you obtain a device context (retrieved by GetDC, or GetWindowDC functions), you may write to the window. At the end of this process the device context must be released using ReleaseDC. Otherwise you will have a memory leak.

GDI Black Book: remember, use the ReleaseDC function only for a display device context that was retrieved from the GDI device-context cache. After you"re done with the memory device context, you must free it by using the DeleteDC function.

Finally:

  • use ReleaseDC for forms (the hwnd used as the first parameter)
  • use DeleteDC for memory device contexts (e.g. CreateCompatibleDC function)