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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 advancment.
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."""
...
```
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