Plugins API

This guide consists of multiple sections, first we discuss Wikitude SDK Plugins in general, than we talk about platform specifics and how to register a plugin with the Wikitude SDK and then we go through each of the sample plugins included with the Wikitude Example Applications.

About Wikitude SDK Plugins

Technically a plugin is a class, either written in C++ or Java, that is derived from the Wikitude Plugin base class. Beside lifecycle handling and options to enable and disable the plugin, the Plugin class has four main methods that you can override cameraFrameAvailable which is called each time the camera has a new frame, update which is called after each image recognition cycle as well as startRender and endRender which are called before and after the Wikitude SDK does its rendering.

The most important thing to remember when working with plugins is that they need to have a unique identifier! If the attempt is made to register a plugin with an identifier that is already known to the Wikitude SDK, the register method call will return false.

Plugin Base Class

class Plugin {
      Plugin(std::string identifier_);
      string getIdentifier() const; // returns a unique plugin identifier
      bool processesColorCameraFrames(); // returns true if the plugins wants to process color frames instead of bw

      void setEnabled(bool enabled_);
      bool isEnabled();

      string callJavaScript(string javaScriptSnippet); // evaluates the given JavaScript snippet in the currently loaded ARchitect World context.

      void initialize(); // called when the plugin is initially added to the Wikitude SDK
      void pause(); // called when the Wikitude SDK is paused e.g. the application state changes from active to background
      void resume(uint pausedTime_); // called when the Wikitude SDK resumes e.g. from background to active state. pausedTime represents the time in milliseconds that the plugin was not updated.
      void destroy(); // called when the plugin is removed from the Wikitude SDK

      void cameraFrameAvailable(const Frame&; cameraFrame_); // called each time the camera has a new frame
      void update(const vector<RecognizedTarget> recognizedTargets_); // called each time the Wikitude SDK renders a new frame

      void startRender(); // called before any Wikitude SDK internal rendering is done
      void endRender(); // called right after any Wikitude SDK internal rendering is done

      string      _identifier;
      bool        _enabled;

With those methods in place your plugin will be able to read the full camera image for your own purpose, where the YUV image is also processed in wikitude’s computer vision engine.

Information about Recognized Targets

In case you have the wikitude SDK running with ongoing image recognition, the plugin API will populate the RecognizedTarget in the update method once an image has been recognized. The plugin can then work with class RecognizedTarget, which wraps the details of the target image in the camera view. With that you can read out the pose of the target image and use it for your purposes. Additionally the call contains the calculated distance to the recognized target

class RecognizedTarget {
      const string&    getIdentifier() const; // the identifier of the target. The identifier is defined when the target is added to a target collection
      const Mat4&      getModelViewMatrix() const; // the model view matrix that defines the transformation of the target in the camera frame (translation, rotation, scale)
      const Mat4&      getProjectionMatrix() const;
      const float      getDistanceToCamera() const; // represents the distance from the target to the camera in millimeter

Passing values from within the plugin to the JavaScript part of your augmented reality experience is done via the addToJavaScriptQueue() method of the Plugin class. Using this function will execute any JavaScript code in the context of your augmented reality experience.

Platform Specifics

Registering Plugins

Barcode and QR code reader

This samples shows a full implementation of the popular barcode library ZBar into the Wikitude SDK. As ZBar is licensed under LGPL2.1 this sample can also be used for other projects.

ZBar is an open source software suite for reading bar codes from various sources, such as video streams, image files and raw intensity sensors. It supports many popular symbologies (types of bar codes) including EAN-13/UPC-A, UPC-E, EAN-8, Code 128, Code 39, Interleaved 2 of 5 and QR Code.

Face Detection

This samples shows how to add face detection to your Wikitude augmented reality experience using OpenCV.