INFO: Nesting Scalable Metafiles (107171)

SUMMARY

The ability to use a metafile Device Context (DC) as the destination DC of a metafile playback is new in Windows 3.1. A metafile can now be played into another metafile, and therefore you can easily place one metafile inside another metafile or copy pieces of one metafile into another.

It is sometimes common for an application to create a metafile that will be passed to another application. In this case, it is likely that the metafile will be scaled. Scalable metafiles can easily be created by using the MM_ANISOTROPIC mapping mode, the SetWindowExt() function, and the SetViewportExt() function. The logical extent of a scalable metafile is defined by the parameters in the SetWindowExt() function. It can be complicated when playing one scalable metafile into another scalable metafile device context. The logical extents of the two metafiles may be different and the desired location of the metafile being played may be offset from the origin of the destination metafile DC. The OffsetWindowOrg() and ScaleViewportExt() functions can be used to alter the metafile DC's attributes in order to play the source metafile correctly into the destination metafile DC. The SaveDC/RestoreDC commands can be used to preserve the metafile DC's attributes while playing the source metafile into it.

MORE INFORMATION

When creating a scalable metafile, you are responsible for setting the logical extent of the metafile by calling SetWindowExt(). When playing back a scalable metafile, the application can set the mapping mode to MM_ANISOTROPIC and call SetViewportExt() to specify the desired size of the metafile. When playing a scalable metafile into another scalable metafile, the ratio of the logical extents must be used to determine how far to offset the window origin, so the metafile will be played in the correct location. Also, the viewport must be scaled accordingly so the metafile being played in the destination metafile DC will be the correct size. Calling SaveDC() before playing the metafile and RestoreDC() after playing the metafile will preserve the attributes of the destination metafile DC.

The following code can be used to play a scalable metafile into another scalable metafile DC. Both the logical extents of the source and destination are needed. The first parameter is the destination metafile DC. The second parameter specifies the metafile that will be played into the destination metafile DC. The next four parameters specify a logical rectangle where the metafile will be played on the destination metafile DC. The two parameters after that specify the logical extents of the destination metafile DC, and the last two parameters are the logical extents of the metafile being played.

Sample Code

   void PlayInMetafile(HDC hdcMeta,HMETAFILE hmf,int nLeftRect,
                    int nTopRect,int nRightRect,int nBottomRect,
                    int xLogExt, int yLogExt, int xHmfLogExt,
                    int yHmfLogExt)

   {

    SaveDC(hdcMeta);
    OffsetWindowOrg(hdcMeta,-MulDiv(nLeftRect, xHmfLogExt,
                    nRightRect-nLeftRect), -MulDiv(nTopRect,
                    yHmfLogExt, nBottomRect-nTopRect));

    ScaleViewportExt(hdcMeta,nRightRect-nLeftRect,xLogExt,
                             nBottomRect-nTopRect,yLogExt);
    PlayMetaFile(hdcMeta,hmf);
    RestoreDC(hdcMeta,-1);

   }