Grue Plugin

Files:

• sensors/grueplugin/gruesensor.cpp
• sensors/grueplugin/gruesensor.h
• sensors/grueplugin/gruesensor_p.h
• sensors/grueplugin/gruesensorimpl.cpp
• sensors/grueplugin/gruesensorimpl.h
• sensors/grueplugin/main.cpp
• sensors/grueplugin/grueplugin.pro

The Grue plugin example demonstrates the creation of a new sensor type, a sensor backend and plugin for the sensors library. Related to this example is the Grue Application example.

Grue Sensor Type

The files for this are:

• gruesensor.h
• gruesensor_p.h
• gruesensor.cpp

First up is the sensor type. This is the interface for sensors that report on your likelihood of being eaten by a Grue. Such sensors are very important to adventurers, particularly if they are going into dark places as this is where Grues live.

The interface is a simple one. It provides only 1 piece of information, your chance of being eaten. For the details on how this is property should be interpreted please see the documentation in gruesensor.cpp.

This example was created using the make_sensor.pl script which can be found in src/sensors. As such, it contains some generated code that defines the convenience classes GrueFilter and GrueSensor.

Grue Sensor Backend

The files for this are:

• gruesensorimpl.h
• gruesensorimpl.cpp

The Grue sensor needs a backend before it can be used. The backend provided is rather basic and it relies on some kind of light sensor to work but it gets the job done. If new hardware that can detect the actual presence of Grues becomes available a backend could be created that supports this hardware and applications using the Grue sensor would be able to use it without any changes.

There are a few mandatory parts to a backend. They are the start and stop methods and the setReading call. The start and stop methods are used to start and stop any underlying hardware. In the case of this backend they start and stop a light sensor. In the start method, the backend should be sure to call the sensorStopped() or sensorBusy() methods if it cannot start.

     lightSensor->setDataRate(sensor()->dataRate());
     lightSensor->start();
     // If the light sensor doesn't work we don't work either
     if (!lightSensor->isActive())
         sensorStopped();
     if (lightSensor->isBusy())
         sensorBusy();

The setReading method is needed so that the sensors library knows where the readings are coming from. This backend has a local copy of the reading so it passes a pointer to the function.

     // Register our reading instance
     setReading<GrueSensorReading>(&m_reading);

However it is also possible to pass null to the setReading method in which case the sensors library will create an instance and return a pointer.

 // Create a reading instance for us to use
 m_reading = setReading<GrueSensorReading>(0);

The Grue sensor backend also supplies some metadata.

The backend checks 2 things, how dark it is and how long you have been in the dark. It uses the readingChanged() signal to know when to check the light sensor's value. Once it is dark, it uses a timer to increase your chance of being eaten.

Grue Sensor Plugin

The files for this are:

• main.cpp

The Grue sensor backend is delivered as a plugin. The plugin has a factory object that registers the types available and does the actual instantiation of the backend.