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<html>
<head>
<meta http-equiv="Content-Language" content="en-us">
<link rel="stylesheet" type="text/css" href="../style.css">
<title>Canvas</title>
</head>
<body>
<h1>Canvas</h1>
<p>The canvas represents the drawing surface. It could be anything: a file, a
client area inside a window in a Window System, a paper used by a printer,
etc. Each canvas has its own attributes. </p>
<h3>Initialization</h3>
<p>You must call <b>cdCreateCanvas</b> to create a canvas, and <b>cdKillCanvas</b> when you do not need the canvas anymore.
It is not necessary to activate
a canvas using <b>cdCanvasActivate</b>, but some drivers may require that
call. </p>
<p>To know if a feature is supported by a driver, use function
<strong>cdContextCaps</strong> or see the driver's
documentation.</p>
<h3>Control</h3>
<p>Some canvases are buffered and need to be flushed; for that, use the <b>cdCanvasFlush</b> function. In some drivers, this function can also be used to
change to another page, as in drivers <b>CD_PRINTER</b> and <b>CD_PS</b>.
</p>
<p>You can clear the drawing surface with the <b>cdCanvasClear</b> function,
but in some drivers the function may just draw a rectangle using the
background color. </p>
<h3>Coordinate System</h3>
<p>You may retrieve the original canvas size using the <b>cdCanvasGetSize</b>
function. The canvas' origin is at the bottom left corner of the canvas, but
an origin change can be simulated with function <b>cdCanvasOrigin</b>. Usually
user interface libraries have their origin at the upper right corner, oriented
top down. In this case, the function <strong>cd</strong><b>Canvas</b><strong>UpdateYAxis</strong>
converts the Y coordinate from this orientation to CD's orientation and
vice-versa. </p>
<h3>Other</h3>
<p>Some canvas contents can be interpreted; the <b>cdCanvasPlay</b> function
interprets the contents of a canvas and calls library functions for the
contents to be displayed in the active canvas. </p>
</body>
</html>
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