One colour value of the image may be used as a mask colour which will lead to the automatic
creation of a \helpref{wxMask}{wxmask} object associated to the bitmap object.
+\wxheading{Alpha channel support}
+
+Starting from wxWindows 2.5.0 wxImage supports alpha channel data, that is in
+addition to a byte for the red, green and blue colour components for each pixel
+it also stores a byte representing the pixel opacity. The alpha value of $0$
+corresponds to a transparent pixel (null opacity) while the value of $255$
+means that the pixel is 100\% opaque.
+
+Unlike the RGB data, not all images have the alpha channel and before using
+\helpref{GetAlpha}{wximagegetalpha} you should check if this image contains
+alpha value with \helpref{HasAlpha}{wximagehasalpha}. In fact, currently only
+images loaded from PNG files with transparency information will have alpha
+channel but support for it will be added to the other formats as well (as well
+as support for saving images with alpha channel which is not still implemented
+either).
+
\wxheading{Available image handlers}
The following image handlers are available. {\bf wxBMPHandler} is always
\twocolwidtha{5cm}%
\begin{twocollist}
\twocolitem{\indexit{wxBMPHandler}}{For loading and saving, always installed.}
-\twocolitem{\indexit{wxPNGHandler}}{For loading and saving.}
+\twocolitem{\indexit{wxPNGHandler}}{For loading (including alpha support) and saving.}
\twocolitem{\indexit{wxJPEGHandler}}{For loading and saving.}
\twocolitem{\indexit{wxGIFHandler}}{Only for loading, due to legal issues.}
\twocolitem{\indexit{wxPCXHandler}}{For loading and saving (see below).}
mask information so that bitmaps and images can be converted back
and forth without loss in that respect.
-\func{}{wxImage}{\param{int}{ width}, \param{int}{ height}}
+\func{}{wxImage}{\param{int}{ width}, \param{int}{ height}, \param{bool}{ clear=true}}
-Creates an image with the given width and height.
+Creates an image with the given width and height. If {\it clear} is true, the new image will be initialized to black.
+Otherwise, the image data will be uninitialized.
\func{}{wxImage}{\param{int}{ width}, \param{int}{ height}, \param{unsigned char*}{ data}, \param{bool}{ static\_data=false}}
\membersection{wxImage::Create}\label{wximagecreate}
-\func{bool}{Create}{\param{int}{ width}, \param{int}{ height}}
+\func{bool}{Create}{\param{int}{ width}, \param{int}{ height}, \param{bool}{ clear=true}}
-Creates a fresh image.
+Creates a fresh image. If {\it clear} is true, the new image will be initialized to black.
+Otherwise, the image data will be uninitialized.
\wxheading{Parameters}
\helpref{wxImageHandler}{wximagehandler}
+\membersection{wxImage::GetImageExtWildcard}
+
+\func{static wxString}{GetImageExtWildcard}{\void}
+
+Iterates all registered wxImageHandler objects, and returns a string containing file extension masks
+suitable for passing to file open/save dialog boxes.
+
+\wxheading{Return value}
+
+The format of the returned string is "(*.ext1;*.ext2)|*.ext1;*.ext2".
+
+It is usually a good idea to prepend a description before passing the result to the dialog.
+
+Example:
+
+\begin{verbatim}
+ wxFileDialog FileDlg( this, "Choose Image", ::wxGetWorkingDirectory(), "", _("Image Files ") + wxImage::GetImageExtWildcard(), wxOPEN );
+\end{verbatim}
+
+\wxheading{See also}
+
+\helpref{wxImageHandler}{wximagehandler}
+
+\membersection{wxImage::GetAlpha}\label{wximagegetalpha}
+
+\constfunc{unsigned char}{GetAlpha}{\param{int}{ x}, \param{int}{ y}}
+
+Returns the alpha value for the given pixel. This function may only be called
+for the images with alpha channel, use \helpref{HasAlpha}{wximagehasalpha} to
+check for this.
+
+The returned value is the {\it opacity} of the image, i.e. the value of $0$
+corresponds to the transparent pixels while the value of $255$ -- to the opaque
+ones.
+
+\constfunc{unsigned char *}{GetAlpha}{\void}
+
+Returns pointer to the array storing the alpha values for this image. This
+pointer is {\tt NULL} for the images without the alpha channel. If the image
+does have it, this pointer may be used to directly manipulate the alpha values
+which are stored as the \helpref{RGB}{wximagegetdata} ones.
+
\membersection{wxImage::GetBlue}\label{wximagegetblue}
\constfunc{unsigned char}{GetBlue}{\param{int}{ x}, \param{int}{ y}}
Returns the image data as an array. This is most often used when doing
direct image manipulation. The return value points to an array of
-characters in RGBRGBRGB$\ldots$ format.
+characters in RGBRGBRGB$\ldots$ format in the top-to-bottom, left-to-right
+order, that is the first RGB triplet corresponds to the pixel $(0, 0)$, the
+second one --- to $(0, 1)$ and so on.
You should not delete the returned pointer nor pass it to
\helpref{wxImage::SetData}{wximagesetdata}.
\helpref{wxImage::GetHeight}{wximagegetheight}
+\membersection{wxImage::HasAlpha}\label{wximagehasalpha}
+
+\constfunc{bool}{HasAlpha}{\void}
+
+Returns true if this image has alpha channel, false otherwise.
+
+\wxheading{See also}
+
+\helpref{GetAlpha}{wximagegetalpha}, \helpref{SetAlpha}{wximagesetalpha}
+
\membersection{wxImage::HasMask}\label{wximagehasmask}
\constfunc{bool}{HasMask}{\void}
\helpref{Rescale}{wximagerescale}
+\membersection{wxImage::SetAlpha}\label{wximagesetalpha}
+
+\func{void}{SetAlpha}{\param{unsigned char *}{alpha = {\tt NULL}}}
+
+This function is similar to \helpref{SetData}{wximagesetdata} and has similar
+restrictions. The pointer passed to it may however be {\tt NULL} in which case
+the function will allocate the alpha array internally -- this is useful to add
+alpha channel data to an image which doesn't have any. If the pointer is not
+{\tt NULL}, it must have one byte for each image pixel and be allocated with
+{\tt malloc()}. wxImage takes ownership of the pointer and will free it.
+
+\func{void}{SetAlpha}{\param{int }{x}, \param{int }{y}, \param{unsigned char }{alpha}}
+
+Sets the alpha value for the given pixel. This function should only be called
+if the image has alpha channel data, use \helpref{HasAlpha}{wximagehasalpha} to
+check for this.
+
\membersection{wxImage::SetData}\label{wximagesetdata}
\func{void}{SetData}{\param{unsigned char*}{data}}
the size (width*height*3) or results will be unexpected. Don't use this
method if you aren't sure you know what you are doing.
-The data must have been allocated with malloc(), NOT with operator new.
+The data must have been allocated with {\tt malloc()}, {\large {\bf NOT}} with
+{\tt operator new}.
After this call the pointer to the data is owned by the wxImage object,
that will be responsible for deleting it.
projects / wxWidgets.git / blobdiff