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PDFium

Prerequisites

Get the Chromium depot_tools via the instructions. This provides the gclient utility needed below and many other tools needed for PDFium development.

Also install Python, Subversion, and Git and make sure they're in your path.

Windows development

PDFium uses the same build tool as Chromium:

Open source contributors

Please refer to Chromium's Visual Studio set up for requirements and instructions on build environment configuration.

Run set DEPOT_TOOLS_WIN_TOOLCHAIN=0, or set that variable in your global environment.

Compilation is done through Ninja, not Visual Studio.

CPU Architectures supported

The default architecture for Windows, Linux, and Mac is "x64". On Windows, "x86" is also supported. GN parameter "target_cpu = "x86"" can be used to override the default value. If you specify Android build, the default CPU architecture will be "arm".

It is expected that there are still some places lurking in the code which will not function properly on big-endian architectures. Bugs and/or patches are welcome, however providing this support is not a priority at this time.

Google employees

Run: download_from_google_storage --config and follow the authentication instructions. Note that you must authenticate with your @google.com credentials. Enter "0" if asked for a project-id.

Once you've done this, the toolchain will be installed automatically for you in the Generate the build files step below.

The toolchain will be in depot_tools\win_toolchain\vs_files\<hash>, and windbg can be found in depot_tools\win_toolchain\vs_files\<hash>\win_sdk\Debuggers.

If you want the IDE for debugging and editing, you will need to install it separately, but this is optional and not needed for building PDFium.

Get the code

The name of the top-level directory does not matter. In our examples, we use "repo". This directory must not have been used before by gclient config as each directory can only house a single gclient configuration.

mkdir repo
cd repo
gclient config --unmanaged https://pdfium.googlesource.com/pdfium.git
gclient sync
cd pdfium

Additional build dependencies need to be installed by running the following from the pdfium directory.

./build/install-build-deps.sh

Generate the build files

We use GN to generate the build files and Ninja to execute the build files. Both of these are included with the depot_tools checkout.

Selecting build configuration

PDFium may be built either with or without JavaScript support, and with or without XFA forms support. Both of these features are enabled by default. Also note that the XFA feature requires JavaScript.

Configuration is done by executing gn args <directory> to configure the build. This will launch an editor in which you can set the following arguments. By convention, <directory> should be named out/foo, and some tools / test support code only works if one follows this convention. A typical <directory> name is out/Debug.

use_goma = true  # Googlers only. Make sure goma is installed and running first.
is_debug = true  # Enable debugging features.

# Set true to enable experimental Skia backend.
pdf_use_skia = false
# Set true to enable experimental Skia backend (paths only).
pdf_use_skia_paths = false

pdf_enable_xfa = true  # Set false to remove XFA support (implies JS support).
pdf_enable_v8 = true  # Set false to remove Javascript support.
pdf_is_standalone = true  # Set for a non-embedded build.
is_component_build = false # Disable component build (Though it should work)

clang_use_chrome_plugins = false  # Currently must be false.

For sample applications like pdfium_test to build, one must set pdf_is_standalone = true.

By default, the entire project builds with C++14, because features like V8 support, XFA support, and the Skia backend all have dependencies on libraries that require C++14. If one does not need any of those features, and need to fall back to building in C++11 mode, then set use_cxx11 = true. This fallback is temporary and will go away in the future when PDFium fully transitions to C++14. See this bug for details.

When building with the experimental Skia backend, Skia itself it built with C++17. There is no configuration for this. One just has to use a build toolchain that supports C++17.

When complete the arguments will be stored in <directory>/args.gn, and GN will automatically use the new arguments to generate build files. Should your files fail to generate, please double-check that you have set use_sysroot as indicated above.

Building the code

You can build the sample program by running: ninja -C <directory> pdfium_test You can build the entire product (which includes a few unit tests) by running: ninja -C <directory> pdfium_all.

Running the sample program

The pdfium_test program supports reading, parsing, and rasterizing the pages of a .pdf file to .ppm or .png output image files (Windows supports two other formats). For example: <directory>/pdfium_test --ppm path/to/myfile.pdf. Note that this will write output images to path/to/myfile.pdf.<n>.ppm. Run pdfium_test --help to see all the options.

Testing

There are currently several test suites that can be run:

pdfium_unittests
pdfium_embeddertests
testing/tools/run_corpus_tests.py
testing/tools/run_javascript_tests.py
testing/tools/run_pixel_tests.py

It is possible the tests in the testing directory can fail due to font differences on the various platforms. These tests are reliable on the bots. If you see failures, it can be a good idea to run the tests on the tip-of-tree checkout to see if the same failures appear.

Pixel Tests

If your change affects rendering, a pixel test should be added. Simply add a .in or .pdf file in testing/resources/pixel and the pixel runner will pick it up at the next run.

Make sure that your test case doesn't have any copyright issues. It should also be a minimal test case focusing on the bug that renders the same way in many PDF viewers. Try to avoid binary data in streams by using the ASCIIHexDecode simply because it makes the PDF more readable in a text editor.

To try out your new test, you can call the run_pixel_tests.py script:

$ ./testing/tools/run_pixel_tests.py your_new_file.in

To generate the expected image, you can use the make_expected.sh script:

$ ./testing/tools/make_expected.sh your_new_file.pdf

Please make sure to have optipng installed which optimized the file size of the resulting png.

`.in` files

.in files are PDF template files. PDF files contain many byte offsets that have to be kept correct or the file won't be valid. The template makes this easier by replacing the byte offsets with certain keywords.

This saves space and also allows an easy way to reduce the test case to the essentials as you can simply remove everything that is not necessary.

A simple example can be found here.

To transform this into a PDF, you can use the fixup_pdf_template.py tool:

$ ./testing/tools/fixup_pdf_template.py your_file.in

This will create a your_file.pdf in the same directory as your_file.in.

There is no official style guide for the .in file, but a consistent style is preferred simply to help with readability. If possible, object numbers should be consecutive and /Type and /SubType should be on top of a dictionary to make object identification easier.

Embedding PDFium in your own projects

The public/ directory contains header files for the APIs available for use by embedders of PDFium. We endeavor to keep these as stable as possible.

Outside of the public/ directory, code may change at any time, and embedders should not directly call these routines.

Code Coverage

Code coverage reports for PDFium can be generated in Linux development environments. Details can be found here.

Chromium provides code coverage reports for PDFium here. PDFium is located in third_party/pdfium in Chromium's source code. This includes code coverage from PDFium's fuzzers.

Profiling

Valgrind and other profiling tools do not work correctly with the standard build setup that PDFium uses. You will need to add ro_segment_workaround_for_valgrind=true to args.gn to get symbols to correctly appear.

Waterfall

The current health of the source tree can be found here.

Community

There are several mailing lists that are setup:

Note, the Reviews and Bugs lists are typically read-only.

Bugs

We use this bug tracker, but for security bugs, please use Chromium's security bug template and add the "Cr-Internals-Plugins-PDF" label.

Contributing code

For contributing code, we will follow Chromium's process as much as possible. The main exceptions are:

Code has to conform to the existing style and not Chromium/Google style.
PDFium uses a different Gerrit instance for code reviews, and credentials for this Gerrit instance need to be generated before uploading changes.
PDFium is transitioning to C++14, but still supports C++11 compatibility for the duration of the transition period. Prefer to use only C++11 features, though technically C++14 is allowed in code that is only built when V8, XFA, or Skia is turned on.

Before submitting a fix for a bug, it can help if you create an issue in the bug tracker. This allows easier discussion about the problem and also helps with statistics tracking.

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