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按照官方的说法：Cairo is a vector graphics library with cross-device output support. 翻译过来

------------------------
Unfortunately, the quartz backend code is currently out of date with
respect to some recent backend interface changes. So, the quartz
backend is disabled in this snapshot.

If the quartz backend is brought up-to-date before the next snapshot,
we would be glad to make a 0.4.1 snapshot that re-enables it, (we do
not expect many more big backend interface changes).

API Changes
-----------
The font system has been revamped, (as Owen Taylor's work with
integrating pango and cairo gave us the first serious usage of the
non-toy font API).

One fundamental, user-visible change is that the cairo_font_t object
now represents a font that is scaled to a particular device
resolution. Further changes are described below.

 cairo.h
 -------
 Removed cairo_font_set_transform and cairo_font_current_transform.

 Added cairo_font_extents and cairo_font_glyph_extents. See
 documentation for details:

 http://cairographics.org/manual/cairo-cairo-t.html#cairo-font-extents

 cairo-ft.h
 ----------
 The cairo_ft_font API changed considerably. Please see the
 documentation for details:

 http://cairographics.org/manual/cairo-FreeType-Fonts.html

Performance
-----------
Make the fast-path clipping (pixel-aligned rectangles) faster.

Add optimization for applying a constant alpha to a pattern.

Optimize gradients that are horizontal or vertical in device space.

Xlib: When RENDER is not available, use image surfaces for
intermediate surfaces rather than xlib surfaces.

Backend-specific changes
------------------------
 Glitz
 -----
 Major update to glitz backend. The output quality should now be just
 as good as the image and xlib backends.

 Track changes to glitz 0.4.0.

 PDF
 ---
 Various improvements to produce more conformant output.

Internals
---------
David Reveman contributed a large re-work of the cairo_pattern_t
implementation, providing cleaner code and more optimization
opportunities.

 Backend interface changes
 -------------------------
 Rework backend interface to accept patterns, not surfaces for source
 and mask.

 Remove set_matrix, set_filter, and set_repeat functions.

 More sophisticated backend interface for image fallbacks,
 ({acquire,release}_{source,dest}_image() and clone_similar).

Bug fixes
---------
Only install header files for backends that have been compiled.

Fixed some rounding errors leading to incorrectly placed glyphs.

Many other minor fixes.

Snapshot 0.3.0 (2005-01-21 Carl Worth <[e-mail]>)
==========================================================
Major API changes
-----------------
1) The public header files will no longer be directly installed into
   the system include directory. They will now be installed in a
   subdirectory named "cairo", (eg. in /usr/include/cairo rather than
   in /usr/include).

   As always, the easiest way for applications to discover the
   location of the header file is to let pkg-config generate the
   necessary -I CFLAGS and -L/-l LDFLAGS. For example:

	cc `pkg-config --cflags --libs cairo` -o foo foo.c

   IMPORTANT: Users with old versions of cairo installed will need to
              manually remove cairo.h and cairo-features.h from the
              system include directories in order to prevent the old
              headers from being used in preference to the new ones.

2) The backend-specific portions of the old monolithic cairo.h have
   been split out into individual public header files. The new files
   are:

	cairo-atsui.h
        cairo-ft.h
        cairo-glitz.h
        cairo-pdf.h
        cairo-png.h
        cairo-ps.h
	cairo-quartz.h
        cairo-xcb.h
        cairo-xlib.h

   Applications will need to be modified to explicitly include the new
   header files where appropriate.

3) There are two new graphics backends in this snapshot, a PDF
   backend, and a Quartz backend. There is also one new font backend,
   ATSUI.

PDF backend
-----------
Kristian Høgsberg has contributed a new backend to allow cairo-based
applications to generate PDF output. The interface for creating a PDF
surface is similar to that of the PS backend, as can be seen in
cairo-pdf.h:

	void
	cairo_set_target_pdf (cairo_t	*cr,
			      FILE	*file,
			      double	width_inches,
			      double	height_inches,
			      double	x_pixels_per_inch,
			      double	y_pixels_per_inch);

	cairo_surface_t *
	cairo_pdf_surface_create (FILE		*file,
				  double	width_inches,
				  double	height_inches,
				  double	x_pixels_per_inch,
				  double	y_pixels_per_inch);

Once a PDF surface has been created, applications can draw to it as
any other cairo surface.

This code is still a bit rough around the edges, and does not yet
support clipping, surface patterns, or transparent gradients.  Text
only works with TrueType fonts at this point and only black text is
supported.  Also, the size of the generated PDF files is currently
quite big.

Kristian is still actively developing this backend, so watch this
space for future progress.

Quartz backend
--------------
Calum Robinson has contributed a new backend to allow cairo
applications to target native Mac OS X windows through the Quartz
API. Geoff Norton integrated this backend into the current
configure-based build system, while Calum also provided Xcode build
support in the separate "macosx" module available in CVS.

The new interface, available in cairo-quartz.h, is as follows:

	void
	cairo_set_target_quartz_context (cairo_t	*cr,
					 CGContextRef	context,
					 int		width,
					 int		height);

	cairo_surface_t *
	cairo_quartz_surface_create (CGContextRef context,
				     int	  width,
				     int	  height);

There is an example program available in CVS in cairo-demo/quartz. It
is a port of Keith Packard's fdclock program originally written for
the xlib backend. A screenshot of this program running on Mac OS X is
available here:

	http://cairographics.org/~cworth/images/fdclock-quartz.png

ATSUI font backend
------------------
This new font backend complements the Quartz backend by allowing
applications to use native font selection on Mac OS X. The interface
is a single new function:

	cairo_font_t *
	cairo_atsui_font_create (ATSUStyle style);

Minor API changes
-----------------
Prototype for non-existent function "cairo_ft_font_destroy" removed.

Now depends on libpixman 0.1.2 or newer, (0.1.3 is being released
concurrently and has some useful performance improvements).

Default paint color is now opaque black, (was opaque white). Default
background color is transparent (as before).

Renamed "struct cairo" to "struct _cairo" to free up the word "cairo"
from the C++ identifier name space.

Functions returning multiple return values through provided pointers,
(cairo_matrix_get_affine, cairo_current_point, and
cairo_current_color_rgb), will now accept NULL for values the user
wants to ignore.

CAIRO_HAS_FREETYPE_FONT has now been renamed to CAIRO_HAS_FT_FONT.

Performance improvements
------------------------
Alexander Larsson provided some fantastic performance improvements
yielding a 10000% performance improvement in his application, (when
also including his performance work in libpixman-0.1.3). These include

 * Fixed handling of cache misses.

 * Creating intermediate clip surfaces at the minimal size required.

 * Eliminating roundtrips when creating intermediate Xlib surfaces.

Implementation
--------------
Major re-work of font metrics system by Keith Packard. Font metrics
should now be much more reliable.

Glitz backend
-------------
Updated for glitz-0.3.0.
Bug fixes in reference counting.

Test suite
----------
New tests for cache crashing, rotating text, improper filling of
complex polygons, and leaky rasterization.

Bug fixes
---------
Fixed assertion failure when selecting the same font multiple times in
sequence.

Fixed reference counting so cache_destroy functions work.

Remove unintended copyright statement from files generated with
PostScript backend.

Fixed to eliminate new warnings from gcc 3.4 and gcc 4.

Snapshot 0.2.0 (2004-10-27 Carl Worth <[e-mail]>)
===========================================================
New license: LGPL/MPL
---------------------
The most significant news with this release is that the license of
cairo has changed. It is now dual-licensed under the LGPL and the
MPL. For details see the COPYING file as well as COPYING-LGPL-2.1 and
COPYING-MPL-1.1.

I express my thanks to everyone involved in the license change process
for their patience and support!

New font and glyph internals
----------------------------
Graydon Hoare has put a tremendous amount of work into new internals
for handling fonts and glyphs, including caches where appropriate.
This work has no impact on the user-level API, but should result in
great performance improvements for applications using text.

New test suite
--------------
This snapshot of cairo includes a (small) test suite in
cairo/test. The tests can be run with "make check". The test suite was
designed to make it very easy to add new tests, and we hope to see
many contributions here. As you find bugs, please try adding a minimal
test case to the suite, and submit it with the bug report to the
[e-mail] mailing list. This will make it much easier
for us to track progress in fixing bugs.

New name for glitz backend
--------------------------
The gl backend has now been renamed to the glitz backend. This means
that the following names have changed:

	CAIRO_HAS_GL_SURFACE    -> CAIRO_HAS_GLITZ_SURFACE
	cairo_set_target_gl     -> cairo_set_target_glitz
	cairo_gl_surface_create -> cairo_glitz_surface_create

This change obviously breaks backwards compatibility for applications
using the old gl backend.

Up-to-date with latest glitz snapshots
--------------------------------------
This snapshot of cairo is now up to date with the latest glitz
snapshot, (currently 0.2.3). We know that the latest cairo and glitz
snapshots have been incompatible for a very long time. We've finally
fixed that now and we're determined to not let that happen again.

Revert some tessellation regression bugs
----------------------------------------
People that have been seeing some tessellation bugs, (eg. leaked
fills), in the CVS version of cairo may have better luck with this
release. A change since the last snapshot was identified to trigger
some of these bugs and was reverted before making the snapshot. The
behavior should be the same as the previous (0.1.23) snapshot.

Miscellaneous changes
---------------------
Changed CAIRO_FILTER_DEFAULT to CAIRO_FILTER_BEST to make gradients
easier.

Track XCB API change regarding iterators.

Various bug fixes
-----------------
Fix calculation of required number of vertices for pen.

Fix to avoid zero-dimensioned pixmaps.

Fix broken sort of pen vertices.

Fix bug when cairo_show_text called with a NULL string.

Fix clipping bugs.

Fix bug in computing image length with XCB.

Fix infinite loop bug in cairo_arc.

Fix memory management interactions with libpixman.

Snapshot 0.1.23 (2004-05-11 Carl Worth <[e-mail]>)
========================================================
Fixes for gcc 3.4
-----------------
Fix prototype mismatches so that cairo can be built by gcc 3.4.

Updates to track glitz
----------------------
Various fixes to support the latest glitz snapshot (0.1.2).

Gradient updates
----------------
Radial gradients now support both inner and outer circles.
Transformed linear gradients are now properly handled.
Fixes for extend type reflect.

Glitz updates
-------------
Converted shading routines to use fixed point values and introduced a
shading operator structure for more efficient shading calculations.
Support compositing with mask surface when mask is solid or
multi-texturing is available.

PNG backend cleanups
--------------------
Fix output to properly compensate for pre-multiplied alpha format in cairo.
Add support for A8 and A1 image formats.

Bug fixes
---------
Avoid crash or infinite loop on null strings and degeneratively short
splines.

New? bugs in cairo_clip
-----------------------
There are some fairly serious bugs in cairo_clip. It is sometimes
causing an incorrect result. And even when it does work, it is
sometimes so slow as to be un