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checklist-gdkeventexpose-region.html
<!DOCTYPE html PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN"> <html> <head> <meta http-equiv="Content-Type" content="text/html; charset=UTF-8"> <title>Use GdkEventExpose.region: GTK+ 3 Reference Manual</title> <meta name="generator" content="DocBook XSL Stylesheets V1.79.1"> <link rel="home" href="index.html" title="GTK+ 3 Reference Manual"> <link rel="up" href="gtk-migrating-checklist.html" title="Migration Details Checklist"> <link rel="prev" href="gtk-migrating-checklist.html" title="Migration Details Checklist"> <link rel="next" href="checklist-modifiers.html" title="Test for modifier keys correctly"> <meta name="generator" content="GTK-Doc V1.32 (XML mode)"> <link rel="stylesheet" href="style.css" type="text/css"> </head> <body bgcolor="white" text="black" link="#0000FF" vlink="#840084" alink="#0000FF"> <table class="navigation" id="top" width="100%" summary="Navigation header" cellpadding="2" cellspacing="5"><tr valign="middle"> <td width="100%" align="left" class="shortcuts"></td> <td><a accesskey="h" href="index.html"><img src="home.png" width="16" height="16" border="0" alt="Home"></a></td> <td><a accesskey="u" href="gtk-migrating-checklist.html"><img src="up.png" width="16" height="16" border="0" alt="Up"></a></td> <td><a accesskey="p" href="gtk-migrating-checklist.html"><img src="left.png" width="16" height="16" border="0" alt="Prev"></a></td> <td><a accesskey="n" href="checklist-modifiers.html"><img src="right.png" width="16" height="16" border="0" alt="Next"></a></td> </tr></table> <div class="section"> <div class="titlepage"><div><div><h2 class="title" style="clear: both"> <a name="checklist-gdkeventexpose-region"></a>Use GdkEventExpose.region</h2></div></div></div> <p><b>Why. </b> The <em class="structfield"><code>region</code></em> field of <span class="structname">GdkEventExpose</span> allows you to redraw less than the traditional <em class="structfield"><code>GdkEventRegion.area</code></em>. </p> <p> In early GTK+ versions, the <span class="structname">GdkEventExpose</span> structure only had an <em class="structfield"><code>area</code></em> field to let you determine the region that you needed to redraw. In current GTK+, this field still exists for compatibility and as a simple interface. However, there is also a <em class="structfield"><code>region</code></em> field which contains a fine-grained region. The <em class="structfield"><code>area</code></em> field is simply the bounding rectangle of the <em class="structfield"><code>region</code></em>. </p> <p> Widgets that are very expensive to re-render, such as an image editor, may prefer to use the <em class="structfield"><code>GdkEventExpose.region</code></em> field to paint as little as possible. Widgets that just use a few drawing primitives, such as labels and buttons, may prefer to use the traditional <em class="structfield"><code>GdkEventExpose.area</code></em> field for simplicity. </p> <p> Regions have an internal representation that is accessible as a list of rectangles. To turn the <em class="structfield"><code>GdkEventExpose.region</code></em> field into such a list, use <code class="function">gdk_region_get_rectangles()</code>: </p> <a name="gdkregion-get-rectangles"></a><pre class="programlisting"> static gboolean my_widget_expose_event_handler (GtkWidget *widget, GdkEventExpose *event) { GdkRectangle *rects; int n_rects; int i; gdk_region_get_rectangles (event->region, &rects, &n_rects); for (i = 0; i < n_rects; i++) { /* Repaint rectangle: (rects[i].x, rects[i].y), * (rects[i].width, rects[i].height) */ } g_free (rects); return FALSE; } </pre> </div> <div class="footer"> <hr>Generated by GTK-Doc V1.32</div> </body> </html>