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Linux/Unix下的绘图函数库（Graphic Drawing Library）

setting the gdFTEX_FONTPATHNAME flag
in the flag element of the gdFTStringExtra structure. Thanks to
Dag Lem and John Ellson.
<li>Additional freetype fixes: fixed width fonts are now the right
size, horizontal advance calculations now better match the
PostScript equivalent, and various compiler warning fixes. Also,
a fix to the encoding table selection in the was made, addressing a problem
with latin1 font encodings. Thanks to Dag Lem and John Ellson. 
<li>Improved tolerance when reading JPEG files containing some garbage as well
as valid image data.
<li>Easier compilation on Windows: no errno.h in gd_gd2.c.
<li>Support for creating optimized GIF animations has been added
 by Jaakko Hyv&auml;tti.  See
 <A HREF="#gdImageGifAnimAdd">gdImageGifAnimAdd</A>,
 <A HREF="#gdImageGifAnimAddCtx">gdImageGifAnimAddCtx</A>,
 <A HREF="#gdImageGifAnimAddPtr">gdImageGifAnimAddPtr</A>,
 <A HREF="#gdImageGifAnimBegin">gdImageGifAnimBegin</A>,
 <A HREF="#gdImageGifAnimBeginCtx">gdImageGifAnimBeginCtx</A>,
 <A HREF="#gdImageGifAnimBeginPtr">gdImageGifAnimBeginPtr</A>,
 <A HREF="#gdImageGifAnimEnd">gdImageGifAnimEnd</A>,
 <A HREF="#gdImageGifAnimEndCtx">gdImageGifAnimEndCtx</A>, and
 <A HREF="#gdImageGifAnimEndPtr">gdImageGifAnimEndPtr</A>.
<li><A HREF="#gdImageOpenPolygon">gdImageOpenPolygon</A> has been
 added to allow consecutive line segments to be drawn without
 connecting the end points to form a closed polygon. Thanks to
Jaakko Hyv&auml;tti.
<li>Better alpha channel blending when the destination color
contains an alpha channel. Also, quicker handling of the
most common cases. Thanks to Frank Warmerdam.
</ul>
<P>
<A NAME="whatsnew2.0.28"><H3>What's new in version 2.0.28?</H3></A>
<P>
<ul>
<li>GIF support has been restored. See
<a href="#gdImageGif">gdImageGif</a>, 
<a href="#gdImageGifCtx">gdImageGifCtx</a>, 
<a href="#gdImageGifPtr">gdImageGifPtr</a>, 
<a href="#gdImageCreateFromGif">gdImageCreateFromGif</a>, 
<a href="#gdImageCreateFromGifCtx">gdImageCreateFromGifCtx</a>, 
and <a href="#gdImageCreateFromGifPtr">gdImageCreateFromGifPtr</a>.
These functions are now thread-safe, similar to the PNG and JPEG
manipulation functions.
<li>The new <a href="#gdImageCreatePaletteFromTrueColor">gdImageCreatePaletteFromTrueColor</a> function is identical to <a href="#gdImageTrueColorToPalette">gdImageTrueColorToPalette</a>, except that it returns a new image rather than permanently modifying the original.
</ul>
<P>
<A NAME="whatsnew2.0.27"><H3>What's new in version 2.0.27?</H3></A>
<P>
<ul>
<li>In gd 2.0.26, there was potential for out of bounds fills, and therefore
crashes, in the horizontalLine function used by gdImageFilledPolygon.
Fixed by John Ellson.
<li>The order of the points returned in the bounding rectangle by
gdImageStringFT was incorrect in version 2.0.26. This has been
corrected in version 2.0.27. Thanks to Riccardo Cohen for pointing
this out, and to John Ellson for verifying and fixing it.
</ul>
<P>
<A NAME="whatsnew2.0.26"><H3>What's new in version 2.0.26?</H3></A>
<P>
The following enhancements and fixes:
<ul>
<li>Drastically faster, less memory-intensive antialiased drawing, thanks to
Pierre-Alain Joye. This code was imported from the PHP "fork"
of gd. The API for antialiased drawing has not changed, however the
implementation has been completely replaced.
Antialiased line drawing does not support widths other
than 1, however this did not work properly with the other
implementation of antialiasing either. Support has been included
for the "non-blending color" option introduced by the previous
implementation of antialiased drawing.
<li><code>gdlib-config</code>, which has been installed by 
<code>make install</code> for some time now, has gained
a <code>--features</code> option. This option produces a space-separated
list of optional features with which the gd library was compiled.
Typical usage looks like this:
<pre>
% gdlib-config --features
GD_XPM GD_JPEG GD_FREETYPE GD_PNG GD_GIF
</pre>
Other <code>configure</code> scripts can conveniently define
preprocessor symbols based on this list in order to conditionally
compile code. For instance, if
GD_PNG is not reported by --features, then gdImagePng is not
included in the library.
<p>
Thanks to Lars Hecking and Lincoln Stein for their advice on
implementing this feature. Any blame for the actual implementation
is entirely due to me (TBB).
<li>Fixes to the behavior of the bounding rectangle returned by
gdImageStringFT and relatives when the string is rotated.
See fontwheeltest.c. Thanks to John Ellson.
<li>Previously, gdImageStringFT and friends accepted either 
a full path to a font file, or the name of a font with no
extension, in which case the GDFONTPATH environment variable
and then the compiled-in DEFAULT_FONTPATH was searched. In addition,
a font filename with an extension but no full path can now be
automatically searched for in the same fashion. Thanks to John Ellson.

<li>Fixes to freetype antialiased text against a transparent 
background. See testtr.c. Thanks to John Ellson.

<li>Support for named entities like &amp;amp; and hex-coded 
entities such as &amp;#x6C34; in text 
strings passed to gdImageStringFT and relatives, adding to the 
previous support for decimal-coded entities like &amp;#197;. 
These were extracted from entities.html (from the W3C) via
the script entities.tcl, which is included for the curious and
those with other entities they need support for.  Thanks to John Ellson.

<li>Optimization: gdImageSetPixel no longer calls gdImageAlphaBlend 
when either the source or the destination pixel is 100% transparent. 
Thanks to John Ellson.

<li>Optimization: gdImageLine is potentially faster now in the most 
common cases.
Thanks to John Ellson.
<li>Documentation of the entities feature of gdImageStringFT.
<li>autoconf/configure fixes. Thanks to many who pointed out an oversight
in handling libpng flags.
</ul>
<P>
<A NAME="whatsnew2.0.25"><H3>What's new in version 2.0.25?</H3></A>
<P>
Owing to an oversight while making changes to better accommodate the use
of gd as a DLL, the <b>extern</b> qualifier was dropped from the 
declarations of font pointers in 2.0.24. This has been corrected.
Thanks to Richard ("OpenMacNews").
<P>
<A NAME="whatsnew2.0.24"><H3>What's new in version 2.0.24?</H3></A>
<P>
<b>Windows DLL now uses __stdcall calling convention.</b> Existing
applications will require a recompile, using the new version of gd.h,
in order to use this version of the DLL. However, Visual BASIC and other
non-C programmers will now be able to use the DLL, which is an enormous
benefit and justifies the one-time inconvenience to existing DLL users. 
<p>
The elaborate #ifdef test for older versions of Freetype without
FT_ENCODING_MS_SYMBOL was needed in a second place also. Thanks to
David R. Morrison.
<p>
An off-by-one error in gdImageToPalette caused transparency to be applied
to the wrong pixels. Thanks to "Super Pikeman."
<P>
<A NAME="whatsnew2.0.23"><H3>What's new in version 2.0.23?</H3></A>
<P>
Output dpi specification option added to the
<code>gdFTStringExtra</code> structure, thanks to
Mark Shackelford. See <a href="#gdImageStringFTEx">gdImageStringFTEx</a>.
<P>
<A NAME="whatsnew2.0.22"><H3>What's new in version 2.0.22?</H3></A>
<P>
<ul>
<li>Win32 DLL users: working with pointers exported by DLLs is 
difficult and causes unexpected results. gd 2.0.22 exports new
functions for retrieving the basic gd fonts:
<a href="#gdFontGetTiny">gdFontGetTiny()</a>,
<a href="#gdFontGetSmall">gdFontGetSmall()</a>,
<a href="#gdFontGetMediumBold">gdFontGetMediumBold()</a>,
<a href="#gdFontGetLarge">gdFontGetLarge()</a>, and
<a href="#gdFontGetHuge">gdFontGetHuge()</a>. You may safely assign the
return values from these functions to a local <code>gdFontPtr</code>.
Direct use of <code>gdFontLarge</code>, etc. is strongly deprecated
for users of <code>bgd.dll</code>; use these new functions instead.
<li>Basic support for loading CMYK-colorspace JPEG images. They are
of course converted to RGB which is a lossy process, however the
results do look quite good and are certainly fine for thumbnails and
web previews of DTP work.
<li>"make" no longer fails on <code>circletexttest</code> if 
PNG support is missing. 
<li>Small performance improvements to gdImageCopyResampled; larger
improvements are forthcoming.
</ul>
<P>
<A NAME="whatsnew2.0.21"><H3>What's new in version 2.0.21?</H3></A>
<P>
<ul>
<li>Version 2.0.21 adds a <code>gdImageCreateFrom*Ptr</code> family
of functions which make it convenient to load an image in any
GD-supported format directly from memory.
<li>The new <code>gdNewDynamicCtxEx</code> function was added to
support the easy implementation of the above functions and to
correct a design problem which made life unpleasant for those passing
in memory not originally allocated by gd to the 
<code>gdNewDynamicCtx</code> function by provoding a way to specify
that gd should never free or reallocate a particular block of memory.
The <code>gdNewDynamicCtx</code> function and its relatives, although
still exported for ABI compatibility, are now <b>deprecated</b> except 
for internal use, in favor of <a href="#gdImageCreateFromPngPtr"><code>gdImageCreateFromPngPtr</code></a>
and its relatives.
<li>Version 2.0.21 includes a new patch from Ethan A. Merritt to
correct a bug in the conditional compilation of support for
symbol fonts in gdft.c. Symbol fonts should now work correctly.
Thanks to Mr. Merritt.
<li>Version 2.0.20 restores the <code>gdFreeFontCache</code> function,
an undocumented function added in an earlier release which now simply
calls <code>gdFontCacheShutdown</code> for backwards compatibility.
This repairs build problems when compiling PHP against the latest gd.
<li>Documentation improvements.
</ul>
<P>
<A NAME="whatsnew2.0.20"><H3>What's new in version 2.0.20?</H3></A>
<P>
<ul>
<li>Version 2.0.20 restores the <code>gdFreeFontCache</code> function,
an undocumented function added in an earlier release which now simply
calls <code>gdFontCacheShutdown</code> for backwards compatibility.
This repairs build problems when compiling PHP against the latest gd.
</ul>
<P>
<A NAME="whatsnew2.0.19"><H3>What's new in version 2.0.19?</H3></A>
<P>
<ul>
<li>Version 2.0.19 restored <code>extern</code> declarations for the
gd font pointers inadvertently removed in 2.0.18.
</ul>
<P>
<A NAME="whatsnew2.0.18"><H3>What's new in version 2.0.18?</H3></A>
<P>
<ul>
<li>A Win32 binary distribution of "bgd.dll," built with mingw32 and
tested with win32 versions of the demo programs as console applications,
is now available.
<li>Semicolon rather than space used as the default separator of
alternative font file paths in <a href="#gdImageStringFT">gdImageStringFT</a>,
for better compatibility with Windows and other environments where
spaces are common in paths.
<li>The circletexttest demo no longer fails to compile when JPEG
support happens to be absent.
</ul>
<P>
<A NAME="whatsnew2.0.17"><H3>What's new in version 2.0.17?</H3></A>
<P>
Minor compilation and packaging problems with 2.0.16 were corrected.
If 2.0.16 compiled without errors for you, then you don't need
to upgrade to 2.0.17.
<P>
<A NAME="whatsnew2.0.16"><H3>What's new in version 2.0.16?</H3></A>
<P>
<ul>
<li>Thread safety for freetype text output. Background: all gd functions
were already thread safe, as long as only one thread manipulates each
image -- except for gdImageStringFT and gdImageStringFTEx. This is because
of a shared freetype font cache. Sharing the cache between images
is worthwhile, so "configure" now detects pthreads and uses it to
wrap freetype text output in a critical section if available. There is
also critical section support under WIN32. Those who wish to be
strictly thread-safe should call the new function
<a href="#gdFontCacheSetup">gdFontCacheSetup</a> before allowing any
thread to use freetype text calls. Otherwise this function is automatically
invoked on the first use of freetype, with a very small but real chance
of a race condition.
<li><a href="#gdImageSquareToCircle">gdImageSquareToCircle</a> performs
a "polar coordinate transform," returning a new image in which the
X axis of the original has been remapped to theta (angle) and the
Y axis of the original has been remapped to rho (distance from center).
<li><a href="#gdImageStringFTCircle">gdImageStringFTCircle</a> wraps
text in a circle around a specified center point. This function 
takes advantage of <a href="#gdImageSquareToCircle">gdImageSquareToCircle</a>.
The result is very smooth, although it takes some time to compute.
Thanks to Steve Bassi for sponsoring this work.
<li><a href="#gdImageSharpen">gdImageSharpen</a>, contributed by
Paul Troughton. Thank you.
<li>Christophe Thomas corrected gdft.c to include freetype header
files in the way that is now mandatory in freetype 2.1.6 and above.
<li>Gustavo Scotti fixed a memory leak in gdft.c.
<li>Clipping rectangle respected in freetype text output. Thanks to Matt