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<!doctype HTML PUBLIC "-//IETF//DTD HTML//EN">
<html>
<head>
<meta http-equiv="Content-Language" content="en-us">
<meta http-equiv="Content-Type" content="text/html; charset=iso-8859-1">
<title>X-Windows</title>
<link rel="stylesheet" type="text/css" href="../../style.css">
<style type="text/css">
.style1 {
font-family: Courier;
}
</style>
</head>
<body>
<h2>X-Windows Base Driver</h2>
<p>This driver represents a basic driver for all system-dependent drivers
implemented in the X-Windows system. The implementation uses the XLIB API
functions. It was developed using X11R4, but works in more recent versions,
such as X11R6.</p>
<p>Note: The coordinates internally implemented by the video driver use 16-bit
integers. Therefore, if a coordinate with less than -32k or more than 32k is
defined, it will be interpreted incorrectly.</p>
<h3>Behavior of Functions</h3>
<h4>Control </h4>
<ul>
<li><a href="../func/other.html#cdPlay">
<font face="Courier"><strong>Play</strong></font></a>: does nothing, returns
<font face="Courier">CD_ERROR</font>. </li>
</ul>
<h4>Coordinate System and Clipping </h4>
<ul>
<li>
<a href="../func/coordinates.html#cdUpdateYAxis">
<font face="Courier"><strong>UpdateYAxis</strong></font></a>: the
orientation of axis Y is the opposite to its orientation in the CD library.</li>
</ul>
<h4>Primitives</h4>
<ul>
<li><a href="../func/text.html#cdText"><font face="Courier"><strong>Text</strong></font></a>:
text orientation is simulated using XVertex rotines. Generic transformation
matrix affects only the position of the text.</li>
<li><a href="../func/lines.html#cdBegin">
<font face="Courier"><strong>Begin</strong></font></a>: Filled
polygons have an error of one pixel to the right and below. <strong><tt>
CD_BEZIER</tt></strong> is simulated with lines.</li>
<li><span class="style1"><a href="../func/marks.html#cdMark">
<strong>Box</strong></a></span>: in Linux with ATI board, is being drawn with one
extra pixel to the right and below.</li>
</ul>
<h4>Attributes </h4>
<ul>
<li>
<a href="../func/lines.html#cdLineWidth">
<font face="Courier"><strong>LineWidth</strong></font></a>: if
<font face="Courier">width</font> is 1, the driver will use 0 for a better
performance.</li>
<li>
<a href="../func/lines.html#cdLineStyle">
<font face="Courier"><strong>LineStyle</strong></font></a>: thick lines have
style only in the line's direction. For example, you will see small rectangles
in a thick dotted line.</li>
<li>
<a href="../func/text.html#cdNativeFont">
<font face="Courier"><strong>NativeFont</strong></font></a>: also accepts the
X-Windows font string format. You can use program <strong>xfontsel</strong> to select a font and obtain the string.
For ex: "-*-times-bold-r-*-*-24-*-*-*-*-*-*-*" (equivalent of <strong>Font</strong>("Times",
CD_BOLD, -24).</li>
<li><a href="../func/text.html#cdFont">
<font face="Courier"><strong>Font</strong></font></a>: the old name "System"
is mapped to "fixed".</li>
</ul>
<h4>Colors </h4>
<ul>
<li>
<a href="../func/color.html#cdPalette">
<font face="Courier"><strong>Palette</strong></font></a>: When the number of
bits per pixel is smaller than or equal to 8, the driver will use the system
palette to solve colors passed as parameters to the canvas. The driver
allocates colors as they are requested - if a color cannot be allocated, the
closest color is used in the palette. For such, the driver sees all available
colors, in the current application and others. If one of the applications is
terminated, a color in the palette may become invalid and will only be updated
by the driver when it is requested again. For this reason, a call to <strong>
cdForeground </strong>or <strong>cdBackground</strong> or <strong>cdPalette</strong>
is recommended before drawing.<br>
When CD_FORCE is used, the driver forces color allocation in the X server.
This may imply changing colors in other applications when a cursor moves in
and out of the canvas. However, if the number of requested colors is smaller
than the maximum number of possible colors in the palette, then the first
colors in the default system palette will be preserved, minimizing this
problem.<br>
When CD_POLITE is used, all colors allocated by the driver are liberated, and
the requested colors are allocated. This is useful for the application to
prioritize the colors that will be allocated, causing other colors to be
mapped to their closest colors.<br>
Note that canvases in the same application interfere with one another, but
when a canvas is terminated it liberates all allocated colors.</li>
</ul>
<h4>Client Images</h4>
<ul>
<li>
<a href="../func/client.html#cdGetImageRGB">
<font face="Courier"><strong>GetImageRGB</strong></font></a>: can be very
slow due to the heavy conversions performed to translate data in system format
into RGB vectors. </li>
</ul>
<h4>Exclusive Attributes</h4>
<ul>
<li>"<b><font face="Courier">GC</font></b>": returns the X11 graphics
context (get only). In Lua is returned as a user data.</li>
</ul>
<ul>
<li>"<b><font face="Courier">ROTATE</font></b>": allows the usage of 1
angle and 1 coordinate (x, y), that define a global rotation transformation
centered in the specified coordinate. Use 1 real and 2 integer values inside a
string ("%g %d %d" = angle x y). In this driver will change the
current transformation matrix, if removed will reset the current
transformation matrix.</li>
</ul>
</body>
</html>
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