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<!DOCTYPE html PUBLIC "-//W3C//DTD HTML 4.0 Transitional//EN"><html> <head> <title> GnomeCanvas </title> <meta name="GENERATOR" content= "Modular DocBook HTML Stylesheet Version 1.45"> <link rel="HOME" title="GTK+ / Gnome Application Development" href="ggad.html"> <link rel="UP" title="Advanced GTK+/Gnome Techniques" href= "advanced.html"> <link rel="PREVIOUS" title="Other Examples" href="z171.html"> <link rel="NEXT" title="Basic Canvas Architecture" href= "z174.html"> </head> <body bgcolor="#FFFFFF" text="#000000" link="#0000FF" vlink= "#840084" alink="#0000FF"> <div class="NAVHEADER"> <table width="100%" border="0" bgcolor="#ffffff" cellpadding= "1" cellspacing="0"> <tr> <th colspan="4" align="center"> <font color="#000000" size="2">GTK+ / Gnome Application Development</font> </th> </tr> <tr> <td width="25%" bgcolor="#ffffff" align="left"> <a href="z171.html"><font color="#0000ff" size="2"><b> <<< Previous</b></font></a> </td> <td width="25%" colspan="2" bgcolor="#ffffff" align= "center"> <font color="#0000ff" size="2"><b><a href="ggad.html"> <font color="#0000ff" size="2"><b> Home</b></font></a></b></font> </td> <td width="25%" bgcolor="#ffffff" align="right"> <a href="z174.html"><font color="#0000ff" size="2"><b> Next >>></b></font></a> </td> </tr> </table> </div> <div class="CHAPTER"> <h1> <a name="CHA-CANVAS"><tt class="CLASSNAME"> GnomeCanvas</tt></a> </h1> <div class="TOC"> <dl> <dt> <b>Table of Contents</b> </dt> <dt> <a href="cha-canvas.html#Z173">Introduction to the Canvas</a> </dt> <dt> <a href="z174.html">Basic Canvas Architecture</a> </dt> <dt> <a href="z177.html">Using the Canvas</a> </dt> <dt> <a href="sec-itemreference.html">Standard Canvas Item Reference</a> </dt> </dl> </div> <p> This chapter describes the <tt class="CLASSNAME"> GnomeCanvas</tt> widget, and the standard canvas items that come with Gnome. The following chapter discusses in more detail how to write a custom canvas item. </p> <div class="SECT1"> <h1 class="SECT1"> <a name="Z173">Introduction to the Canvas</a> </h1> <p> The canvas widget is a powerful and extensible object-oriented display engine, useful in a wide variety of Gnome applications. The widget itself is simply a blank area; you can place <span class="STRUCTNAME"> GnomeCanvasItem</span>s on it. A <span class= "STRUCTNAME">GnomeCanvasItem</span> is a <span class= "STRUCTNAME">GtkObject</span> representing some element of the display, such as an image, a rectangle, an ellipse, or some text. You can refer to this architecture as <i class="FIRSTTERM">structured graphics</i>; the canvas lets you deal with graphics in terms of items, rather than an undifferentiated grid of pixels. Since a <span class="STRUCTNAME">GnomeCanvasItem</span> is a <span class="STRUCTNAME">GtkObject</span>, you can create your own subclasses to supplement those that come with Gnome. This gives you quite a bit of flexibility. Using custom canvas items, the canvas can render almost anything. At the same time, you can use stock canvas items to save time and effort. The canvas puts you in control. </p> <p> <tt class="CLASSNAME">GnomeCanvas</tt> has two modes, representing a quality/speed tradeoff. In "GDK" mode, canvas items render directly to a <span class= "STRUCTNAME">GdkPixmap</span> buffer using the GDK drawing primitives. The canvas copies the buffer to the screen once all items are rendered. In antialiased or "AA" mode, the canvas items write RGB pixels to a vector of bytes; after all the items have drawn on the RGB buffer, the canvas copies it to the screen. This RGB buffer mode is called "antialiased" mode because all the standard canvas items draw to the RGB buffer using the high-quality antialiased routines in <tt class= "APPLICATION">libart_lgpl</tt>. This results in smooth lines and very high display quality, with some cost in speed. </p> </div> </div> <div class="NAVFOOTER"> <br> <br> <table width="100%" border="0" bgcolor="#ffffff" cellpadding= "1" cellspacing="0"> <tr> <td width="25%" bgcolor="#ffffff" align="left"> <a href="z171.html"><font color="#0000ff" size="2"><b> <<< Previous</b></font></a> </td> <td width="25%" colspan="2" bgcolor="#ffffff" align= "center"> <font color="#0000ff" size="2"><b><a href="ggad.html"> <font color="#0000ff" size="2"><b> Home</b></font></a></b></font> </td> <td width="25%" bgcolor="#ffffff" align="right"> <a href="z174.html"><font color="#0000ff" size="2"><b> Next >>></b></font></a> </td> </tr> <tr> <td colspan="2" align="left"> <font color="#000000" size="2"><b>Other Examples</b></font> </td> <td colspan="2" align="right"> <font color="#000000" size="2"><b>Basic Canvas Architecture</b></font> </td> </tr> </table> </div> </body></html>⌨️ 快捷键说明
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