2edb0bdef6
git-svn-id: https://svn.wxwidgets.org/svn/wx/wxWidgets/trunk@15779 c3d73ce0-8a6f-49c7-b76d-6d57e0e08775
63 lines
2.4 KiB
TeX
63 lines
2.4 KiB
TeX
\chapter{Images and bitmaps}\label{chapimages}
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\pagenumbering{arabic}%
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\setheader{{\it CHAPTER \thechapter: IMAGES AND BITMAPS}}{}{}{}{}{{\it CHAPTER \thechapter: IMAGES AND BITMAPS}}%
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\setfooter{\thepage}{}{}{}{}{\thepage}%
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\section{The basics of images and bitmaps}
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Both wxImage and wxBitmap represent what would commonly be referred as
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a photo with a given number of pixels - in contrast to a drawing consisting
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of a collection of lines, curves, circles, squares etc.
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The difference between a wxImage and a wxBitmap is that wxImage is a
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platform and screen independent representation of an image - every
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pixel is always represented by three bytes, one for red, one for green
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and one for blue, thus yielding the classical RGB acronym. Due to the
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simplicity of wxImage, you will do all kinds of image manipulation
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with this class, this includes loading images in various formats
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such as GIF, TIFF or JPEG (these and some more are supported by wxWindows
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without further work), analyzing the image in terms of colour usage etc
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and applying filters to the image for higher-level manipulation, such
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as blurring, sharpening etc.
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The problem with wxImage is that you cannot draw it, i.e. its destiny
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is to live its shadow life in memory, without ever being seen by man.
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If you ever want to draw an image to screen, you have to convert it
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to a wxBitmap first, typically, this will look like this:
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\begin{verbatim}
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wxImage image( 200, 200 );
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wxBitmap bitmap( image.ConvertToBitmap() );
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wxClientDC dc( this )
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dc.DrawBitmap( bitmap );
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\end{verbatim}
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Note, that such as image conversion is an extremely expensive operation
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and you are very well advised to avoid having to call this routine
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more than absolutely required. In practice, you should not do this
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in a paint event handler, for instance.
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There is one more thing you can do with a wxBitmap: you can draw into
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it like you would do with a window. All you need to do is set up a
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proper device context (DC) for it and ensure that you clean up the
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DC correctly afterwards:
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\begin{verbatim}
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wxBitmap bitmap( 200, 200 );
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wxMemoryDC dc;
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dc.SelectObject( bitmap );
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dc.SetPen( *wxBLACK_PEN );
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dc.DrawLine( 0, 0, 199, 199 );
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dc.SelectObject( wxNullBitmap );
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\end{verbatim}
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\section{wxImage built-in features}
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You can save it, load it, get access to it, assign it a mask colour,
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turn it around, mirror it.
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