How does ardiono IDE compile successfully？(ESP32-CAM)

[GE_Rita]

board : ESP32-CAM
environment ：arduino IDE(1.8.10)
esp32 core : 1.0.4
PC：win10

When I want to learn about the function of face detection and recognition yesterday，I found that there was no (.c) file to explain this function.
So, I wonder why it managed to compile without this (.c) file.
Or where do I find its (.c)file.(More important)

More detail:
The path of face detection and recognition lib in my computer:

• C:\Users\ASUS\AppData\Local\Arduino15\packages\esp32\hardware\esp32\1.0.4\tools\sdk\include\esp-face

The contents of the folder are shown below:


The (.c)file link I can find on the internet:
esp-face

It's really amazing.
Hope to get your help.
Thank you!

[GE_Rita]

Finally, I got the answer here.