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<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 3.2//EN"><html> <head> <title>Introduction to Painting Concepts (The Java™ Tutorials > Creating a GUI with JFC/Swing > Performing Custom Painting)</title><style type="text/css"> .FigureCaption { margin-left: 1in; margin-right: 1in; font-family: sans-serif; font-size: smaller; text-align: justify; } #TopBar_bl { background: url(../../images/java_bar_bl.gif) 0 100% no-repeat; width: 100%; height: 60px; } #TopBar_br { background: url(../../images/java_bar_br.gif) 100% 100% no-repeat; width: 100%; height: 60px; } #TopBar_tl { background: url(../../images/java_bar_tl.gif) 0 0 no-repeat; width: 100%; height: 60px; } #TopBar_tr { background: url(../../images/java_bar_tr.gif) 100% 0 no-repeat; width: 100%; height: 60px; } #TopBar { background: #35556B url(../../images/java_bar.gif); margin: 10px 10px 0 10px; height:60px; min-width:700px; color: white; font-family: sans-serif; font-weight: bold; } @media print { #BreadCrumbs, #Download { display: none; } } #TopBar_right { line-height: 14px; 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var main = document.getElementById("MainFlow"); var toggle = document.getElementById("ToggleLeft"); if (b) { contents.className = "LeftBar_shown"; main.className = "MainFlow_indented"; toggle.innerHTML = "Hide the TOC"; document.cookie = 'tutorial_showLeftBar=yes; path=/'; } else { contents.className = "LeftBar_hidden"; main.className = "MainFlow_wide"; toggle.innerHTML = "Show the TOC"; document.cookie = 'tutorial_showLeftBar=no; path=/'; } } function toggleLeft() { showLeft(document.getElementById("LeftBar").className == "LeftBar_hidden"); document.getElementById("ToggleLeft").blur(); } function load() { showLeft(leftBar()); document.getElementById("ToggleLeft").style.display="inline"; } </script> </head><body onload="load()"> <div id=TopBar> <div id=TopBar_tr> <div id=TopBar_tl> <div id=TopBar_br> <div id=TopBar_bl> <div id=TopBar_right> <a target="_blank" href="http://java.sun.com/javase/6/download.jsp">Download the JDK</a> <br> <a href="../../search.html" target="_blank">Search the Tutorials</a> <br> <a href="javascript:toggleLeft()" id="ToggleLeft">Hide the TOC</a> </div> </div> </div> </div> </div> </div> <div class=PrintHeaders> <b>Trail:</b> Creating a GUI with JFC/Swing <br><b>Lesson:</b> Performing Custom Painting </div> <div id=LeftBar class=LeftBar_shown> <div id=Contents> <div class="linkLESSON"><a href="index.html">Performing Custom Painting</a></div><div class="linkAHEAD"><a href="concepts.html">How Swing Components Are Displayed</a></div><div class="nolinkAHEAD">Introduction to Painting Concepts</div><div class="linkAHEAD"><a href="practice.html">Implementing a Custom Component</a></div><div class="linkAHEAD"><a href="summary.html">Summary</a></div><div class="linkAHEAD"><a href="problems.html">Solving Common Painting Problems</a></div></div> </div> <div id=MainFlow class=MainFlow_indented> <span id=BreadCrumbs> <a href=../../index.html target=_top>Home Page</a> > <a href=../index.html target=_top>Creating a GUI with JFC/Swing</a> > <a href=index.html target=_top>Performing Custom Painting</a> </span> <div class=NavBit> <a target=_top href=concepts.html>« Previous</a> • <a target=_top href=../TOC.html>Trail</a> • <a target=_top href=practice.html>Next »</a> </div> <div id=PageTitle>Introduction to Painting Concepts</div> <blockquote>This section gives an overviewof what you need to knowbefore you write code that paints Swing components.It concentrates on the coordinate system, including how borders restrict the coordinates available for painting,and on the <code>Graphics</code> objectpassed in to paint methods.Although most of the API discussed isn't specific to Swing components,we concentrate onwhat <code>JComponent</code>s need.For information on actually painting,you should refer to the API documentation for the<a class="APILink" target="_blank" href="http://java.sun.com/javase/6/docs/api/java/awt/Graphics.html"><code>Graphics</code></a> class and to the<a class="TutorialLink" target="_top" href="../../2d/index.html">2D Graphics</a> trail.</blockquote><h3><a name="coord">The Coordinate System</a></h3><blockquote>Each component has its own integer coordinate system,ranging from (0, 0) to (<em>width</em> - 1, <em>height</em> - 1),where <em>width</em> and <em>height</em>are the size of the component in pixels.As the following figure shows,the upper left corner of a component's painting area is (0, 0).The <em>x</em> coordinate increases to the right,and the <em>y</em> coordinate increases downward.<p><center><IMG SRC="../../figures/uiswing/painting/13ui33.gif" WIDTH="254" HEIGHT="137" ALIGN="BOTTOM" ALT="A component's coordinate system."></center></p><p>When painting, you must take into account not only the component's sizebut also the size of the component's border, if any.For example, a border that paints a one-pixel linearound a componenteffectively changes the top leftmost corner of the component's non-background painting area from (0,0)to (1,1) andreduces the width and the height of the painting area by two pixels each (one pixel per side).The following figure demonstrates this:⌨️ 快捷键说明
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