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Overview

Say there’s an existing component service that does almost everything you want it to, but there’s some slight changes you wish you could make. Luckily, SIC’s object-oriented architecture enables you to inherit from and extend the component you wish to modify. Let’s take the ‘detect’ function of the FaceDetectionComponent service, for example:

    def detect(self, image):
        img = array(image).astype(np.uint8)

        gray = cv2.cvtColor(img, cv2.COLOR_RGB2GRAY)

        faces = self.faceCascade.detectMultiScale(
            gray,
            scaleFactor=1.2,
            minNeighbors=5,
            minSize=(int(self.params.minW), int(self.params.minH)),
        )

        faces = [BoundingBox(x, y, w, h) for (x, y, w, h) in faces]

        return BoundingBoxesMessage(faces)

In this function the ‘scaleFactor’ and ‘minNeighbors’ variables are hidden within the function, meaning the only way to access or change them is to rewrite themthe function. However, rather than rewriting the whole entire FaceDetectionComponent, we can simply create a new component where we inherit from the FaceDetectionComponent, and change just the detect function.

Outline

To extend an existing component we will go through the following steps:

1. Identify the component we wish to change.

2. Create a new script called ‘custom_{COMPONENT_NAME}.py'.

3. Import the original component and relevant modules in the new custom component.

4. Extend the original component, rewrite the functions you wish to change.

5. Change the SICConnector and SICComponentManager to match the new component name.

6. Import the new connector for the custom component in your scripts that use it.

7. Run the new custom component in place of the old one.

Setup (steps 1 and 2)

First, we have already decided we are going to change the ‘detect’ function of the FaceDetectionComponent. So secondlynext, we create a ‘custom_components’ folder in our repo if we do not have one already, and within that add a ‘custom_{COMPONENT}’ script:

...

...

Now run ‘pip install -e .’ within your SIC repository. This will create a link in your environment to the custom_components folder so that you can easily import your custom components within your other scripts.

Writing the new component (steps 3, 4, and 5)

Inside the new custom component script, we import the old component, as well as the SICComponentManager, SICConnector, and anything the new custom component may need:

...

class CustomFaceDetectionComponent(FaceDetectionComponent):
    def __init__(self, *args, **kwargs):
        super(CustomFaceDetectionComponent, self).__init__(*args, **kwargs)
        self.scaleFactor = 1.2
        self.minNeighbors = 3

    def detect(self, image):
        # Override the detect function with custom behavior
        img = array(image).astype(np.uint8)

        gray = cv2.cvtColor(img, cv2.COLOR_RGB2GRAY)

        faces = self.faceCascade.detectMultiScale(
            gray,
            scaleFactor=self.scaleFactor,  # Example of different scale factornow these variables belong to the class
            minNeighbors=self.minNeighbors,    # Example of different minNeighborsthey can be accessed and changed outside this function
            minSize=(int(self.params.minW), int(self.params.minH)),
        )

        faces = [BoundingBox(x, y, w, h) for (x, y, w, h) in faces]

        return BoundingBoxesMessage(faces)

...

class CustomFaceDetection(SICConnector):
    component_class = CustomFaceDetectionComponent # make sure to change the component name here

def main():
    # register the custom component in the component manager
    SICComponentManager([CustomFaceDetectionComponent])

if __name__ == "__main__":
    main()

Using the new component (step 6)

The work on the new custom component is done. Now, you must change the scripts that you want to use the new component. Here the demo_desktop_camera_facedetection.py is used as an example.

First, make sure your script is able to find your new component. Here is one way of doing so:

import sys
from pathlib import Path
# Get the absolute path to the custom_services folder
custom_services_path = Path(__file__).resolve().parent.parent.parent / "custom_components"
sys.path.append(str(custom_services_path))

Alternatively, you can append the ‘custom_components' folder path to the PYTHONPATH environment variable within the ‘activate’ script of your virtual environment. For example:

export PYTHONPATH="/path/to/custom_components:$PYTHONPATH"

Next, import the new connector rather than the old one

...

import the new connector rather than the old one

### from sic_framework.services.face_detection.face_detection import FaceDetection
from custom_components.custom_face_detection import CustomFaceDetection

...

### face_rec = FaceDetection()
face_rec = CustomFaceDetection()

Run the component (step 7)

Run the new component in a separate shell as if it were the old service (assuming you’re inside ‘custom_components') folder:

...