1. Draw the main part of the mask first, as shown in the following figure:
2. Because the mask is axisymmetric, we must draw the center line, as shown in the following figure:
3. Draw the nose clip strip, as shown in the following figure:
4. Around the periphery of the mask, we locate four points, as shown in the following figure:
5. As shown in the following figure:
7. Start drawing the breathing valve, as shown in the following figure:
8. The breathing valve is a combination of a circle and a square, as shown in the following figure:
9. The outside of the breathing valve is hollowed out, and we want to show this feature, as shown in the following figure:
1. Continue to add details, as shown in the following figure:
11.