vcl/README.GDIMetaFile

GDIMetaFile class
=================

The GDIMetaFile class reads, writes, manipulates and replays metafiles via the VCL module.

A typical use case is to initialize a new GDIMetaFile, open the actual stored metafile and
read it in via GDIMetaFile::Read( aIStream ). This reads in the metafile into the GDIMetafile
object - it can read in an old-style VCLMTF metafile (back in the days that Microsoft didn't
document the metafile format this was used), as well as EMF+ files - and adds them to a list
(vector) of MetaActions. You can also populate your own GDIMetaFile via AddAction(),
RemoveAction(), ReplaceAction(), etc.

Once the GDIMetafile object is read to be used, you can "play" the metafile, pause it, wind
forward or rewind the metafile. The metafile can be moved, scaled, rotated and clipped, as
well have the colours adjusted or replaced, or even made monochrome.

The GDIMetafile can be used to get an OutputDevice's metafile via the Linker() and Record()
functions.


Using GDIMetafile
-----------------

First, create a new GDIMetafile, this can be done via the default constructor. It can then
be constructed manually, or you can use Record() on an OutputDevice to populate the
GDIMetaFile, or of course you can read it from file with Read(). From here you can then
elect to manipulate the metafile, or play it back to another GDIMetafile or to an
OutputDevice via Play(). To store the file, use Write().

CONSTRUCTORS AND DESTRUCTORS

- GDIMetaFile
- GDIMetaFile( cosnt GDIMetaFile& rMtf ) - copy constructor
- ~GDIMetaFile


OPERATORS

- operator =
- operator ==
- operator !=


RECORDING AND PLAYBACK FUNCTIONS

- Play(GDIMetaFile&, size_t)               - play back metafile into another metafile up
                                             to position
- Play(OutputDevice*, size_t)              - play back metafile into OutputDevice up to
                                             position
- Play(OutputDevice*, Point, Size, size_t) - play back metafile into OutputDevice at a
                                             particular location on the OutputDevice, up
                                             to the position in the metafile
- Pause                                    - pauses or continues the playback
- IsPause
- Stop                                     - stop playback fully
- WindStart                                - windback to start of the metafile
- windPrev                                 - windback one record
- GetActionSize                            - get the number of records in the metafile


METAFILE RECORD FUNCTIONS

- FirstAction                              - get the first metafile record
- NextAction                               - get the next metafile record from the
                                             current position
- GetAction(size_t)                        - get the metafile record at location in file
- GetCurAction                             - get the current metafile record
- AddAction(MetaAction*)                   - appends a metafile record
- AddAction(MetaAction*, size_t)           - adds a metafile record to a particular
                                             location in the file
- RemoveAction                             - removes record at file location
- Clear                                    - first stops if recording, then removes all
                                             metafile records
- push_back                                - pushes back, basically a thin wrapper to the
                                             metafile record list


READ AND WRITING

- Read
- Write
- GetChecksum
- GetSizeBytes


DISPLACEMENT FUNCTIONS

- Move( long nX, long nX)
- Move( long nX, long nX, long nDPIX, long nDPIY ) - Move method getting specifics how to
                                             handle MapMode( MapUnit::MapPixel )


TRANSFORMATION FUNCTIONS

- Scale( double fScaleX, double fScaleY )
- Scale( const Fraction& rScaleX, const Fraction& rScaleY )
- Mirror
- Rotate( long nAngle10 )
- Clip( const Rectangle& )


COLOR ADJUSTMENT FUNCTIONS

- Adjust                                    - change luminance, contrast, gamma and RGB via a
                                              percentage
- Convert                                   - colour conversion
- ReplaceColors
- GetMonochromeMtf


Related classes
---------------

MetaAction: a base class used by all records. It implements a command-like pattern, and also
acts as a prototype for other actions.


CONSTRUCTORS AND DESTRUCTORS

- MetaAction()                              - default constructor, sets mnRefCount to 1 and
                                              mnType, in this case MetaActionType::NONE
- MetaAction(sal_uInt16 nType)              - virtual constructor, sets mnType to nType, and
                                              mnRefCount to 1
- ~MetaAction


COMMAND FUNCTION

- Execute(OutputDevice*)                    - execute the functionality of the record to the
                                              OutputDevice. Part of command pattern. 


FACTORY FUNCTION

- Clone()                                   - prototype clone function


MANIPULATION FUNCTIONS

- Move(long nHorzMove, long nVerMove)
- Scale(double fScaleX, double fScaleY)


READ AND WRITE FUNCTIONS

- Read
- Write
- ReadMetaAction                            - a static function, only used to determine which
                                              MetaAction to call on to read the record, which
                                              means that this is the function that must be used.


INTROSPECTIVE FUNCTIONS

- GetType



A note about MetaCommentAction: 
-------------------------------

So this class is the most interesting - a comment record is what is used to extended metafiles, to
make what we call an "Enhanced Metafile". This basically gets the OutputDevice's connect metafile
and adds the record via this when it runs Execute(). It doesn't actually do anything else, unlike
other MetaActions which invoke functions from OutputDevice. And if there is no connect metafile in
OutputDevice, then it just does nothing at all in Execute. Everything else works as normal (Read,
Write, etc).



Basic pseudocode
----------------

The following illustrates an exceptionally basic and incomplete implementation of how to use
GDIMetafile. An example can be found at vcl/workben/mtfdemo.cxx


DemoWin::Paint()
{
    // assume that VCL has been initialized and a new application created

    Window* pWin = new WorkWindow();
    GDIMetaFile* pMtf = new GDIMetaFile();

    SvFileStream aFileStream("example.emf", STEAM_READ);

    ReadWindowMetafile(aFileStream, pMtf);
    pMtf->Play(pWin);
    
}