Using Win32 functions in Visual FoxPro Image Gallery
Device Context
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ChangeDisplaySettings
CreateCompatibleDC
CreateDC
DeleteDC
DeleteObject
EnumDisplayDevices
EnumDisplaySettings
GetDC
GetDeviceCaps
GetObject
GetObjectType
ReleaseDC
SelectObject
Code examples:
Bitmap Class for Visual FoxPro application
Converting twips to pixels and vice versa
Copying picture of the active form to the Clipboard using Enhanced Metafile API functions
Creating a clipping region from the path selected into the device context of a form
Creating a window using CreateWindowEx function
Displaying animated images on FoxPro form with BitBlt and StretchBlt functions
Displaying bitmap using the AlphaBlend function
Displaying the associated icons and descriptions for files and folders
Drawing a rectangle using Windows regular edges and borders
Drawing a window caption using the DrawCaption routine
Drawing cursors for the classes defined by the system (preregistered): BUTTON, EDIT, LISTBOX etc.
Drawing icons associated with the VFP main window
Drawing standard Windows icons
Drawing Windows frame controls using the DrawFrameControl function
Drawing Windows predefined bitmaps using the LoadBitmap functions
Form Magnifier
GDI+ fun: roach-infested desktop
GDI+: Color Transparency
GDI+: copying to the Clipboard (a) image of active FoxPro window/form, (b) image file
GDI+: Creating thumbnails to preview images in a directory
GDI+: custom control, base class
GDI+: how to make VFP controls visually shake and shudder
GDI+: Implementing image scrolling with inertia
GDI+: saving image of FoxPro form to graphics file (BMP, GIF, JPG, PNG, TIF)
GDI+: Scrolling through large image using the mouse
GDI+: sending image of FoxPro form to printer
How to change the name and the size of the font in the MessageBox dialog
How to copy the image of a form to the Clipboard using Bitmap API functions
How to display picture stored in enhanced-format metafile (*.emf)
How to find which fonts Windows uses for drawing captions, menus and message boxes
How to make a VFP form fading out when released (GDI version)
How to make a VFP form fading out when released (GDI+ version)
How to play AVI file on the _screen
How to print a bitmap file
How to print FoxPro form
How to print FoxPro form -- II
How to print picture stored in enhanced-format metafile (*.emf)
How to put a horizontal text scrolling on the form (a news line, marquee)
How to put a vertical text scrolling on the form (a movie cast)
How to view icons stored in executable files (Icon Viewer)
How to view icons stored in executable files (Icon Viewer) - II
Obtaining the bounding rectangle for the specified device context
Placing an arbitrary rectangular area of main VFP window on the Clipboard
Placing On-screen Alert on top of all windows
Printing text on the client area of the main VFP window
Printing text on the main VFP window
Printing text with the Escape function
Reading metrics for the currently selected font
Retrieving graphic capabilities of your display
Splash Screen for the VFP application
Storing content of the Clipboard to a bitmap file
Storing screen shot of a form to bitmap file
Storing screen shot of a form to enhanced metafile (*.emf)
Subclassing CommandButton control to create BackColor property
Using Font and Text functions
Using FrameRgn for displaying system colors
Using GetNearestColor
Using the DrawText function
Using the GradientFill function
Using the LoadImage function to have a bitmap file loaded and displayed on VFP main window
Vertical Label control
ReleaseDC
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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:
GDI+: copying to the Clipboard (a) image of active FoxPro window/form, (b) image file
GDI+: Implementing image scrolling with inertia
How to copy the image of a form to the Clipboard using Bitmap API functions
Displaying the associated icons and descriptions for files and folders
Placing On-screen Alert on top of all windows
GDI+: how to make VFP controls visually shake and shudder
Creating a window using CreateWindowEx function
How to make a VFP form fading out when released (GDI+ version)
How to make a VFP form fading out when released (GDI version)
GDI+: Scrolling through large image using the mouse
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
My comment:
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)
Word Index links for the ReleaseDC :
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Created: 2001-07-12 12:00:00
Modified: 2002-11-28 11:13:46
Visited in last 7 days: 60
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