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Bitmaps and icons overview

Classes: wxBitmap, wxBitmapHandler, wxIcon, wxCursor.

The wxBitmap class encapsulates the concept of a platform-dependent bitmap, either monochrome or colour. Platform-specific methods for creating a wxBitmap object from an existing file are catered for, and this is an occasion where conditional compilation will sometimes be required.

A bitmap created dynamically or loaded from a file can be selected into a memory device context (instance of wxMemoryDC). This enables the bitmap to be copied to a window or memory device context using wxDC::Blit, or to be used as a drawing surface. The wxToolBarSimple class is implemented using bitmaps, and the toolbar demo shows one of the toolbar bitmaps being used for drawing a miniature version of the graphic which appears on the main window.

See wxMemoryDC for an example of drawing onto a bitmap.

The following shows the conditional compilation required to load a bitmap under Unix and in Windows. The alternative is to use the string version of the bitmap constructor, which loads a file under Unix and a resource or file under Windows, but has the disadvantage of requiring the XPM icon file to be available at run-time.

#if defined(__WXGTK__) || defined(__WXMOTIF__)
#include "mondrian.xpm"
#endif
A macro, wxICON, is available which creates an icon using an XPM on the appropriate platform, or an icon resource on Windows.

wxIcon icon(wxICON(mondrian));

// Equivalent to:

#if defined(__WXGTK__) || defined(__WXMOTIF__)
wxIcon icon(mondrian_xpm);
#endif

#if defined(__WXMSW__)
wxIcon icon("mondrian");
#endif
Supported bitmap file formats
Bitmap format handlers


Supported bitmap file formats

The following lists the formats handled on different platforms. Note that missing or partially-implemented formats can be supplemented by using wxImage to load the data, and then converting it to wxBitmap form.

wxBitmap

Under Windows, wxBitmap may load the following formats:

Under wxGTK, wxBitmap may load the following formats:

Under wxMotif, wxBitmap may load the following formats:

wxIcon

Under Windows, wxIcon may load the following formats:

Under wxGTK, wxIcon may load the following formats:

Under wxMotif, wxIcon may load the following formats:

wxCursor

Under Windows, wxCursor may load the following formats:

Under wxGTK, wxCursor may load the following formats (in additional to stock cursors):

Under wxMotif, wxCursor may load the following formats:


Bitmap format handlers

To provide extensibility, the functionality for loading and saving bitmap formats is not implemented in the wxBitmap class, but in a number of handler classes, derived from wxBitmapHandler. There is a static list of handlers which wxBitmap examines when a file load/save operation is requested. Some handlers are provided as standard, but if you have special requirements, you may wish to initialise the wxBitmap class with some extra handlers which you write yourself or receive from a third party.

To add a handler object to wxBitmap, your application needs to include the header which implements it, and then call the static function wxBitmap::AddHandler. For example:

  #include <wx/pnghand.h>
  #include <wx/xpmhand.h>
  ...
  // Initialisation
  wxBitmap::AddHandler(new wxPNGFileHandler);
  wxBitmap::AddHandler(new wxXPMFileHandler);
  wxBitmap::AddHandler(new wxXPMDataHandler);
  ...

Assuming the handlers have been written correctly, you should now be able to load and save PNG files and XPM files using the usual wxBitmap API.

Note: bitmap handlers are not implemented on all platforms. Currently, the above is only necessary on Windows, to save the extra overhead of formats that may not be necessary (if you don't use them, they are not linked into the executable). Unix platforms have PNG and XPM capability built-in (where supported).