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OpenFrameworks addon for hot-reloading GLSL shader files on the fly
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An openFrameworks addon for hot-reloading shader files on the fly. Utilizes Facebook’s Watchman service to monitor filesystem changes. Tested on macOS, but as long as you can build the dependencies, it should work on your platform.


  • Using this addon will require you to build OpenFrameworks against a newer version of Boost. That shouldn’t screw up any existing projects (because it looks like the newer Boost headers are almost completely backwards compatible), but you’ve been warned. To make this change, open OpenFrameworks -> libs -> openFrameworksCompiled -> project -> osx -> CoreOF.xcconfig, and edit HEADER_BOOST to point to "/usr/local/include" (as opposed to "$(OF_PATH)/libs/boost/include").
  • On macOS, it seems the Watchman dependency will only build for targets of macOS 10.13 and up. Any project wishing to use this addon will need to (in Xcode) navigate to Project -> General -> Deployment Info and change Deployment Target to at least 10.13.

Using this Addon

Note: This currently assumes you’re using Xcode. If you got this built & running on another platform, and want to document it, reach out and I’ll update this guide.

Install Dependencies

  • Install Watchman and its dependencies (namely, you’ll need Folly and its dependencies). On macOS with Homebrew, this should be something along the lines of brew install folly watchman

Project Setup

  • Simply include this as an addon when using the Project Generator, or, if adding manually, be sure to include each source file in Project -> [select target] -> Build Phases -> Compile Sources
  • Add libfolly.dylib, libevent.dylib, libglog.dylib, and libssl.dylib to Project -> [select target] -> General -> Linked Frameworks and Libraries. NOTE: After clicking “+” to add a framework, I had to manually select “Add Other”, and navigate to /usr/local/opt (using cmd+shift+G should help out) to get to these libraries.
  • Add /usr/local/include to Project -> [select target] -> Build Settings -> Header Search Paths

NOTE: This next step may not be necessary based on your project/dependency settings/how far into the future you’re doing this, but as of right now, Xcode defaults to c++11 so you absolutely must change it to build against c++14 at minimum (the -std=c++1z flag below will build against c++17, for example).

  • Add a few C++ compiler flags to your target under Project -> [select target] -> Build Settings -> Other C++ Flags :


  • First, in ofApp.h, we need to add #include "ShaderFileWatcher.h" to the list of includes, and create a public ShaderFileWatcher pointer member in the ofApp class

    class ofApp : public ofBaseApp {
        ShaderFileWatcher* fileWatcher;
        // And obviously you'll be updating a shader:
        ofShader shader;
  • Next, we must instantiate the folly library in our main. The init function requires argc and argv, so we’ll need to expose these parameters in main.cpp by changing

    int main() {…}


    int main(int argc, char** argv) {…}

    and immediately passing these to folly::init(). I'm going to only pass the first argument because of this.

    int main(int argc, char** argv) {
      argc = 1;
      folly::init(&argc, &argv);
  • Awesome! With all of that out of the way, now we can instantiate a fileWatcher which will tell the watchman server to watch a directory of our choosing, and will automatically listen for changes to certain (or any) shader files within that directory. So navigate to ofApp.cpp, and in setup(), initialize the ShaderFileWatcher pointer

    void ofApp::setup() {
      fileWatcher = new ShaderFileWatcher(
                                // 1. Folder containing shader files (default = project/bin/data)
                                // 2. Name of vertex shader to monitor for changes (default = "*.vert")
                                // 3. Name of fragment shader to monitor for changes (default = "*.frag")
                                // 4. Path to your Watchman executable (default = "/usr/local/bin")
  • Lastly, all we have to do is call checkForUpdate(), which will return true if we need to reload our shaders

    void ofApp::update() {
      if (fileWatcher->checkForUpdate()) {
        shader.load("shader.vert", "shader.frag");
  • That’s it! You can now compile openFrameworks once, and write your shaders on the fly (even in a different editor!). Check the example project to see it all put together. Happy shading!

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