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Google Chrome extension that sets an image as desktop wallpaper.
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Set wallpaper extension

This Google Chrome extension adds a context menu to every single image that allows you to set that image as a wallpaper. It allows you to change the style of the wallpaper by simply pressing one of the TILE, CENTER, STRETCH, FILL, and FIT types.


How does it work?

It uses the Google Chrome Extension API to inject context menus to every image. Then once you clicked on an image, it triggers a callback to the background page which opens up the preview page.

The preview page is an HTML5 canvas, where I load the image into the canvas. Once the image loads, we use simple 2D math to figure out where the center is, how to stretch it, and many scaled photos needed to tile. The preview should look like exactly how the image will be scaled on your screen.

When the user chooses save background, it will go to a NPAPI plugin which is programmed in C++ that hooks itself to the Windows API.

How to build?


  • SCons and Python
    • Windows: You may need to modify the PATH environment variable to include <PYTHON_ROOT>\Scripts (where the scons.bat file gets installed).
  • Windows: an installation of Visual Studio. Express versions will work but these are limited to 32bit builds only.
  • Markdown in Python if you want to generate this README from its Markdown source.

Run scons -h for a list of command-line arguments. Of note are:

  • DEBUG: Build the shared-library part of the extension with debugging support.
  • TARGET_ARCH: Can be either x86 (32bit build) or x86_64 (64bit build).
  • CHROME_BIN: Location of the chrome binary. Required if running the extension packaging target.
  • PRIVATE_KEY: Location of the .pem file used for signing a packaged extension. If one isn't provided, a key is created when packaging.


  • unpacked: (Default) Build the shared library part of the extension and install it and all other extension files in a directory called install-<debug|release>-<arch>/set-wallpaper-extension resulting in an 'unpacked' extension that can be loaded with Chrome using Developer Mode. Intermediate files created during the build are placed in build-<debug|release>-<arch>.
  • packed: After building an unpacked extension, package the extension into a .crx file. For this target, the CHROME_BIN construction variable must be set. The PRIVATE_KEY variable provides the path to a signing key to use. If no key is provided, one will be created. The resulting .crx (and .pem file) are placed in install-<debug|release>-<arch>.
  • readme: Use markdown for python to convert into html. Useful for previewing the file before a push.
  • msvs_project: Generate a Visual Studio Project. Refer to the Generating MSVS Projects section below for more details.

The scons documentation can be read for more details but to start a build, the command-line should look something like this:

scons VAR1=value1 VAR2=value2 ... [target]

The target name is optional. If not provided, the default target is used. Build results and intermediate files are placed in a directory with the following format:


This scheme of including the build variant in the directory name enables build results for varying values of the DEBUG and TARGET_ARCH command-line variables to exist at the same time.

Generating MSVS Projects

The msvs_project target is used to build a Visual Studio Project using SCon's built-in functionality. This functionality has some caveats however:

  • The resulting solution file (.sln file) is placed in the build directory with other build results and intermediate files whereas the project files (.vcxproj files) are placed in the source directory.
    • As a result, project files have the build variant as part of their names to prevent naming collisions.

The generated solution file can be opened with Visual Studio to navigate, edit, and build source. Building the project within Visual Studio will invoke scons with the same DEBUG and TARGET_ARCH command-line variable values as were provided when the project files were generated. The result of the build is the NPAPI DLL component of the plugin. Since this DLL is not a stand-alone executable using the run or run-in-debug-mode commands in Visual Studio will cause Visual Studio to complain.

How to debug the plugin

You can debug the extension's Native (NPAPI) instance by setting a property for the plugin:

app.debug = true;

Mohamed Mansour

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