Background
==========
libjpeg-turbo is a JPEG image codec that uses SIMD instructions to accelerate
baseline JPEG compression and decompression on x86, x86-64, ARM, PowerPC, and
MIPS systems, as well as progressive JPEG compression on x86 and x86-64
systems. On such systems, libjpeg-turbo is generally 2-6x as fast as libjpeg,
all else being equal. On other types of systems, libjpeg-turbo can still
outperform libjpeg by a significant amount, by virtue of its highly-optimized
Huffman coding routines. In many cases, the performance of libjpeg-turbo
rivals that of proprietary high-speed JPEG codecs.
libjpeg-turbo implements both the traditional libjpeg API as well as the less
powerful but more straightforward TurboJPEG API. libjpeg-turbo also features
colorspace extensions that allow it to compress from/decompress to 32-bit and
big-endian pixel buffers (RGBX, XBGR, etc.), as well as a full-featured Java
interface.
libjpeg-turbo was originally based on libjpeg/SIMD, an MMX-accelerated
derivative of libjpeg v6b developed by Miyasaka Masaru. The TigerVNC and
VirtualGL projects made numerous enhancements to the codec in 2009, and in
early 2010, libjpeg-turbo spun off into an independent project, with the goal
of making high-speed JPEG compression/decompression technology available to a
broader range of users and developers.
License
=======
libjpeg-turbo is covered by three compatible BSD-style open source licenses.
Refer to [LICENSE.md](LICENSE.md) for a roll-up of license terms.
Building libjpeg-turbo
======================
Refer to [BUILDING.md](BUILDING.md) for complete instructions.
Using libjpeg-turbo
===================
libjpeg-turbo includes two APIs that can be used to compress and decompress
JPEG images:
- **TurboJPEG API**<br>
This API provides an easy-to-use interface for compressing and decompressing
JPEG images in memory. It also provides some functionality that would not be
straightforward to achieve using the underlying libjpeg API, such as
generating planar YUV images and performing multiple simultaneous lossless
transforms on an image. The Java interface for libjpeg-turbo is written on
top of the TurboJPEG API. The TurboJPEG API is recommended for first-time
users of libjpeg-turbo. Refer to [tjexample.c](tjexample.c) and
[TJExample.java](java/TJExample.java) for examples of its usage and to
<http://libjpeg-turbo.org/Documentation/Documentation> for API documentation.
- **libjpeg API**<br>
This is the de facto industry-standard API for compressing and decompressing
JPEG images. It is more difficult to use than the TurboJPEG API but also
more powerful. The libjpeg API implementation in libjpeg-turbo is both
API/ABI-compatible and mathematically compatible with libjpeg v6b. It can
also optionally be configured to be API/ABI-compatible with libjpeg v7 and v8
(see below.) Refer to [cjpeg.c](cjpeg.c) and [djpeg.c](djpeg.c) for examples
of its usage and to [libjpeg.txt](libjpeg.txt) for API documentation.
There is no significant performance advantage to either API when both are used
to perform similar operations.
Colorspace Extensions
---------------------
libjpeg-turbo includes extensions that allow JPEG images to be compressed
directly from (and decompressed directly to) buffers that use BGR, BGRX,
RGBX, XBGR, and XRGB pixel ordering. This is implemented with ten new
colorspace constants:
JCS_EXT_RGB /* red/green/blue */
JCS_EXT_RGBX /* red/green/blue/x */
JCS_EXT_BGR /* blue/green/red */
JCS_EXT_BGRX /* blue/green/red/x */
JCS_EXT_XBGR /* x/blue/green/red */
JCS_EXT_XRGB /* x/red/green/blue */
JCS_EXT_RGBA /* red/green/blue/alpha */
JCS_EXT_BGRA /* blue/green/red/alpha */
JCS_EXT_ABGR /* alpha/blue/green/red */
JCS_EXT_ARGB /* alpha/red/green/blue */
Setting `cinfo.in_color_space` (compression) or `cinfo.out_color_space`
(decompression) to one of these values will cause libjpeg-turbo to read the
red, green, and blue values from (or write them to) the appropriate position in
the pixel when compressing from/decompressing to an RGB buffer.
Your application can check for the existence of these extensions at compile
time with:
#ifdef JCS_EXTENSIONS
At run time, attempting to use these extensions with a libjpeg implementation
that does not support them will result in a "Bogus input colorspace" error.
Applications can trap this error in order to test whether run-time support is
available for the colorspace extensions.
When using the RGBX, BGRX, XBGR, and XRGB colorspaces during decompression, the
X byte is undefined, and in order to ensure the best performance, libjpeg-turbo
can set that byte to whatever value it wishes. If an application expects the X
byte to be used as an alpha channel, then it should specify `JCS_EXT_RGBA`,
`JCS_EXT_BGRA`, `JCS_EXT_ABGR`, or `JCS_EXT_ARGB`. When these colorspace
constants are used, the X byte is guaranteed to be 0xFF, which is interpreted
as opaque.
Your application can check for the existence of the alpha channel colorspace
extensions at compile time with:
#ifdef JCS_ALPHA_EXTENSIONS
[jcstest.c](jcstest.c), located in the libjpeg-turbo source tree, demonstrates
how to check for the existence of the colorspace extensions at compile time and
run time.
libjpeg v7 and v8 API/ABI Emulation
-----------------------------------
With libjpeg v7 and v8, new features were added that necessitated extending the
compression and decompression structures. Unfortunately, due to the exposed
nature of those structures, extending them also necessitated breaking backward
ABI compatibility with previous libjpeg releases. Thus, programs that were
built to use libjpeg v7 or v8 did not work with libjpeg-turbo, since it is
based on the libjpeg v6b code base. Although libjpeg v7 and v8 are not
as widely used as v6b, enough programs (including a few Linux distros) made
the switch that there was a demand to emulate the libjpeg v7 and v8 ABIs
in libjpeg-turbo. It should be noted, however, that this feature was added
primarily so that applications that had already been compiled to use libjpeg
v7+ could take advantage of accelerated baseline JPEG encoding/decoding
without recompiling. libjpeg-turbo does not claim to support all of the
libjpeg v7+ features, nor to produce identical output to libjpeg v7+ in all
cases (see below.)
By passing an argument of `-DWITH_JPEG7=1` or `-DWITH_JPEG8=1` to `cmake`, you
can build a version of libjpeg-turbo that emulates the libjpeg v7 or v8 ABI, so
that programs that are built against libjpeg v7 or v8 can be run with
libjpeg-turbo. The following section describes which libjpeg v7+ features are
supported and which aren't.
### Support for libjpeg v7 and v8 Features
#### Fully supported
- **libjpeg API: IDCT scaling extensions in decompressor**<br>
libjpeg-turbo supports IDCT scaling with scaling factors of 1/8, 1/4, 3/8,
1/2, 5/8, 3/4, 7/8, 9/8, 5/4, 11/8, 3/2, 13/8, 7/4, 15/8, and 2/1 (only 1/4
and 1/2 are SIMD-accelerated.)
- **libjpeg API: Arithmetic coding**
- **libjpeg API: In-memory source and destination managers**<br>
See notes below.
- **cjpeg: Separate quality settings for luminance and chrominance**<br>
Note that the libpjeg v7+ API was extended to accommodate this feature only
for convenience purposes. It has always been possible to implement this
feature with libjpeg v6b (see rdswitch.c for an example.)
- **cjpeg: 32-bit BMP support**
- **cjpeg: `-rgb` option**
- **jpegtran: Lossless cropping**
- **jpegtran: `-perfect` option**
- **jpegtran: Forcing width/height when performing lossless crop**
- **rdjpgcom: `-raw` option**
- **rdjpgcom: Locale awareness**
#### Not supported
NOTE: As of this writing, extensive research has been conducted into the
usefu
QT-6.0.0源码环境 （2000个子文件） 
glslang_tab.cpp 486KB spirv_msl.cpp 455KB Initialize.cpp 451KB spirv_glsl.cpp 433KB hlslParseHelper.cpp 430KB ParseHelper.cpp 382KB GlslangToSpv.cpp 358KB ui4.cpp 171KB spirv_hlsl.cpp 160KB makefile.cpp 149KB spirv_cross.cpp 137KB doc.cpp 136KB Intermediate.cpp 135KB hlslGrammar.cpp 132KB msvc_objectmodel.cpp 120KB main.cpp 120KB cppwriteinitialization.cpp 119KB pbuilder_pbx.cpp 109KB SpvBuilder.cpp 107KB hlslParseables.cpp 88KB intermOut.cpp 85KB unixmake2.cpp 81KB msbuild_objectmodel.cpp 80KB ShaderLang.cpp 78KB spirv_cross_c.cpp 75KB qmakeevaluator.cpp 75KB qmakebuiltins.cpp 75KB linkValidate.cpp 72KB msvc_vcproj.cpp 72KB moc.cpp 71KB Scan.cpp 67KB generator.cpp 64KB Constant.cpp 62KB qprintengine_win.cpp 58KB qmakeparser.cpp 57KB Versions.cpp 55KB rcc.cpp 54KB SPVRemapper.cpp 53KB reflection.cpp 52KB iomapper.cpp 52KB qprintdialog_unix.cpp 52KB Pp.cpp 49KB PpScanner.cpp 49KB qprinter.cpp 48KB qsqltablemodel.cpp 46KB preprocessor.cpp 44KB qsqldatabase.cpp 44KB qdbusxml2cpp.cpp 44KB propagateNoContraction.cpp 41KB makefiledeps.cpp 41KB keywords.cpp 40KB tst_qshaderbaker.cpp 39KB winmakefile.cpp 38KB unixmake.cpp 37KB hlslScanContext.cpp 36KB qspirvshader.cpp 33KB spirv_parser.cpp 31KB qsb.cpp 30KB disassemble.cpp 29KB qpagesetupdialog_unix.cpp 29KB main.cpp 28KB qsqlresult.cpp 28KB qprintpreviewdialog.cpp 27KB option.cpp 27KB qsqlrelationaltablemodel.cpp 26KB qshaderbaker.cpp 25KB qprintpreviewwidget.cpp 25KB msvc_nmake.cpp 24KB qwindowsprintdevice.cpp 23KB ParseContextBase.cpp 22KB cppgenerator.cpp 21KB lalr.cpp 21KB main.cpp 21KB projectgenerator.cpp 20KB qsqlquerymodel.cpp 20KB SpvPostProcess.cpp 20KB spirv_cross_parsed_ir.cpp 20KB spirv_reflect.cpp 20KB main.cpp 19KB metamakefile.cpp 19KB main.cpp 17KB qsqlfield.cpp 17KB qvkgen.cpp 16KB spirv_cpp.cpp 16KB qdbuscpp2xml.cpp 16KB qpaintengine_alpha.cpp 16KB SymbolTable.cpp 15KB main.cpp 15KB mingw_make.cpp 15KB language.cpp 14KB qspirvcompiler.cpp 14KB qmakeglobals.cpp 14KB spirv_cfg.cpp 13KB proitems.cpp 13KB generate_keywords.cpp 13KB sqldatabase.cpp 13KB qabstractprintdialog.cpp 13KB qprinterinfo.cpp 13KB recognizer.cpp 12KB qprintengine_pdf.cpp 12KB共 2000 条
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