Define a context class ====================== The [ArContext](../../../argaze.md/#argaze.ArFeatures.ArContext) class defines a generic base class interface to handle incoming eye tracker data before to pass them to a processing pipeline according to [Python context manager feature](https://docs.python.org/3/reference/datamodel.html#context-managers). The [ArContext](../../../argaze.md/#argaze.ArFeatures.ArContext) class interface provides playback features to stop or pause processings, performance assement features to measure how many times processings are called and the time spent by the process. Besides, there is also a [LiveProcessingContext](../../../argaze.md/#argaze.ArFeatures.LiveProcessingContext) class that inherits from [ArContext](../../../argaze.md/#argaze.ArFeatures.ArContext) and that defines an abstract *calibrate* method to write specific device calibration process. In the same way, there is a [PostProcessingContext](../../../argaze.md/#argaze.ArFeatures.PostProcessingContext) class that inherits from [ArContext](../../../argaze.md/#argaze.ArFeatures.ArContext) and that defines abstract *previous* and *next* playback methods to move into record's frames and also defines *duration* and *progression* properties to get information about a record length and processing advancement. Finally, a specific eye tracking context can be defined into a Python file by writing a class that inherits either from [ArContext](../../../argaze.md/#argaze.ArFeatures.ArContext), [LiveProcessingContext](../../../argaze.md/#argaze.ArFeatures.LiveProcessingContext) or [PostProcessingContext](../../../argaze.md/#argaze.ArFeatures.PostProcessingContext) class. ## Write live processing context Here is a live processing context example that processes gaze positions and camera images in two separated threads: ```python from argaze import ArFeatures, DataFeatures class LiveProcessingExample(ArFeatures.LiveProcessingContext): @DataFeatures.PipelineStepInit def __init__(self, **kwargs): # Init LiveProcessingContext class super().__init__() # Init private attribute self.__parameter = ... @property def parameter(self): """Any context specific parameter.""" return self.__parameter @parameter.setter def parameter(self, parameter): self.__parameter = parameter @DataFeatures.PipelineStepEnter def __enter__(self): """Start context.""" # Start context according any specific parameter ... self.parameter # Start a gaze position processing thread self.__gaze_thread = threading.Thread(target = self.__gaze_position_processing) self.__gaze_thread.start() # Start a camera image processing thread if applicable self.__camera_thread = threading.Thread(target = self.__camera_image_processing) self.__camera_thread.start() return self def __gaze_position_processing(self): """Process gaze position.""" # Processing loop while self.is_running(): # Pause processing if not self.is_paused(): # Assuming that timestamp, x and y values are available ... # Process timestamped gaze position self._process_gaze_position(timestamp = timestamp, x = x, y = y) # Wait some time eventually ... def __camera_image_processing(self): """Process camera image if applicable.""" # Processing loop while self.is_running(): # Pause processing if not self.is_paused(): # Assuming that timestamp, camera_image are available ... # Process timestamped camera image self._process_camera_image(timestamp = timestamp, image = camera_image) # Wait some time eventually ... @DataFeatures.PipelineStepExit def __exit__(self, exception_type, exception_value, exception_traceback): """End context.""" # Stop processing loops self.stop() # Stop processing threads threading.Thread.join(self.__gaze_thread) threading.Thread.join(self.__camera_thread) def calibrate(self): """Handle device calibration process.""" ... ``` ## Write post processing context Here is a post processing context example that processes gaze positions and camera images in a same thread: ```python from argaze import ArFeatures, DataFeatures class PostProcessingExample(ArFeatures.PostProcessingContext): @DataFeatures.PipelineStepInit def __init__(self, **kwargs): # Init LiveProcessingContext class super().__init__() # Init private attribute self.__parameter = ... @property def parameter(self): """Any context specific parameter.""" return self.__parameter @parameter.setter def parameter(self, parameter): self.__parameter = parameter @DataFeatures.PipelineStepEnter def __enter__(self): """Start context.""" # Start context according any specific parameter ... self.parameter # Start a reading data thread self.__read_thread = threading.Thread(target = self.__data_reading) self.__read_thread.start() return self def __data_reading(self): """Process gaze position and camera image if applicable.""" # Processing loop while self.is_running(): # Pause processing if not self.is_paused(): # Assuming that timestamp, camera_image are available ... # Process timestamped camera image self._process_camera_image(timestamp = timestamp, image = camera_image) # Assuming that timestamp, x and y values are available ... # Process timestamped gaze position self._process_gaze_position(timestamp = timestamp, x = x, y = y) # Wait some time eventually ... @DataFeatures.PipelineStepExit def __exit__(self, exception_type, exception_value, exception_traceback): """End context.""" # Stop processing loops self.stop() # Stop processing threads threading.Thread.join(self.__read_thread) def previous(self): """Go to previous camera image frame.""" ... def next(self): """Go to next camera image frame.""" ... ```