Version: 3.1.0
Bitmaps and Icons

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.

See wxMemoryDC for an example of drawing onto a bitmap.

All wxWidgets platforms support XPMs for small bitmaps and icons. You may include the XPM inline as below, since it's C code, or you can load it at run-time.

#include "sample.xpm"

Sometimes you wish to use a .ico resource on Windows, and XPMs on other platforms (for example to take advantage of Windows' support for multiple icon resolutions).

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(sample));
// The above line is equivalent to this:
#if defined(__WXGTK__) || defined(__WXMOTIF__)
wxIcon icon(sample_xpm);
#endif
#if defined(__WXMSW__)
wxIcon icon("sample");
#endif

There is also a corresponding wxBITMAP() macro which allows to create the bitmaps in much the same way as wxICON() creates icons. It assumes that bitmaps live in resources under Windows or OS2 and XPM files under all other platforms (for XPMs, the corresponding file must be included before this macro is used, of course, and the name of the bitmap should be the same as the resource name under Windows with _xpm suffix). For example:

// an easy and portable way to create a bitmap
wxBitmap bmp(wxBITMAP(bmpname));
// which is roughly equivalent to the following
#if defined(__WXMSW__) || defined(__WXPM__)
#else // Unix
wxBitmap bmp(bmpname_xpm, wxBITMAP_TYPE_XPM);
#endif

You should always use wxICON() and wxBITMAP() macros because they work for any platform (unlike the code above which doesn't deal with wxMac, wxX11, ...) and are shorter and more clear than versions with many #ifdef blocks. Alternatively, you could use the same XPMs on all platforms and avoid dealing with Windows resource files.

If you'd like to embed bitmaps with alpha transparency in your program, neither XPM nor BMP formats are appropriate as they don't have support for alpha and another format, typically PNG, should be used. wxWidgets provides a similar helper for PNG bitmaps called wxBITMAP_PNG() that can be used to either load PNG files embedded in resources (meaning either Windows resource section of the executable file or OS X "Resource" subdirectory of the application bundle) or arrays containing PNG data included into the program code itself.

See Also
Graphics Device Interface (GDI)

Supported Bitmap File Formats

The following lists the formats handled on different platforms. Note that missing or partially-implemented formats are automatically supplemented by using wxImage to load the data, and then converting it to wxBitmap form. Note that using wxImage is the preferred way to load images in wxWidgets, with the exception of resources (XPM-files or native Windows resources).

Writing an image format handler for wxImage is also far easier than writing one for wxBitmap, because wxImage has exactly one format on all platforms whereas wxBitmap can store pixel data very differently, depending on colour depths and platform.

wxBitmap

Under Windows, wxBitmap may load the following formats:

@li Windows bitmap resource (wxBITMAP_TYPE_BMP_RESOURCE)
@li Windows bitmap file (wxBITMAP_TYPE_BMP)
@li XPM data and file (wxBITMAP_TYPE_XPM)
@li All formats that are supported by the wxImage class.

Under wxGTK, wxBitmap may load the following formats:

@li XPM data and file (wxBITMAP_TYPE_XPM)
@li All formats that are supported by the wxImage class.

Under wxMotif and wxX11, wxBitmap may load the following formats:

@li XBM data and file (wxBITMAP_TYPE_XBM)
@li XPM data and file (wxBITMAP_TYPE_XPM)
@li All formats that are supported by the wxImage class.

wxIcon

Under Windows, wxIcon may load the following formats:

@li Windows icon resource (wxBITMAP_TYPE_ICO_RESOURCE)
@li Windows icon file (wxBITMAP_TYPE_ICO)
@li XPM data and file (wxBITMAP_TYPE_XPM)

Under wxGTK, wxIcon may load the following formats:

@li XPM data and file (wxBITMAP_TYPE_XPM)
@li All formats that are supported by the wxImage class.

Under wxMotif and wxX11, wxIcon may load the following formats:

@li XBM data and file (wxBITMAP_TYPE_XBM)
@li XPM data and file (wxBITMAP_TYPE_XPM)
@li All formats that are supported by the wxImage class.

wxCursor

Under Windows, wxCursor may load the following formats:

@li Windows cursor resource (wxBITMAP_TYPE_CUR_RESOURCE)
@li Windows cursor file (wxBITMAP_TYPE_CUR)
@li Windows icon file (wxBITMAP_TYPE_ICO)
@li Windows bitmap file (wxBITMAP_TYPE_BMP)

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

@li None (stock cursors only).

Under wxMotif and wxX11, wxCursor may load the following formats:

@li XBM data and file (wxBITMAP_TYPE_XBM)

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().

Note
Bitmap handlers are not implemented on all platforms, and new ones rarely need to be implemented since wxImage can be used for loading most formats, as noted earlier.