INFO: Windows 3.x Metafiles Support DeleteObject()

• Microsoft Windows Software Development Kit (SDK) 3.1

SUMMARY

In versions of Microsoft Windows earlier than 3.0, a metafile that used a large number of brushes or pens could cause the GDI data segment to fill up, which would interfere with playing the metafile. To address this situation, metafiles were extended to support the DeleteObject() API in Windows 3.0.

Standard Windows programming practice dictates that a GDI object, such as a brush or a pen, must be deleted by DeleteObject() when the object is no longer required by an application. This same practice also applies to metafiles. When an application is drawing into a metafile Display Context (DC) and the application no longer requires a GDI object, the application must select the object out of the metafile DC, then call DeleteObject(). An example of this process is provided below.

During the process of creating a metafile, when an object is deleted, Windows inserts a DeleteObject() record into the metafile. When an application plays the metafile, the DeleteObject() record removes unnecessary objects, which prevents the GDI data segment from filling.

Note that if an application calls DeleteObject() for an object that is selected into a metafile DC, the DeleteObject() call will succeed. However, no DeleteObject() record will be placed into the metafile.

MORE INFORMATION

The following code demonstrates the proper method to use and delete GDI objects in a metafile:

   HPEN hPen1, hPen2;
   HDC hMetaDC;     // Metafile DC, assumed already created.

   hPen1 = CreatePen(PS_SOLID, 6, RGB(0, 0, 255));
   SelectObject(hMetaDC, hPen1);          // Select pen into Metafile DC.
   Rectangle(hMetaDC, 10, 10, 100, 100);  // Use hPen1.

   hPen2 = CreatePen(PS_SOLID, 6, RGB(255, 255, 0));
   SelectObject(hMetaDC, hPen2);          // Deselect hPen1 by selecting

                                          // a new pen into the DC.

   DeleteObject(hPen1);                   // Delete hPen1.
   Rectangle(hMetaDC, 100, 100, 150, 150);  // Use hPen2.


   // The metafile is now complete. To deselect the final pen,
   // select in a stock object.

   SelectObject(hMetaDC, GetStockObject(WHITE_PEN));

   // Delete hPen2

   DeleteObject(hPen2); 

Additional query words: 3.00 3.10

Keywords : kb16bitonly kbSDKWin16
Version : WINDOWS:3.1
Platform : WINDOWS
Issue type : kbinfo