For more context on this, https://www.youtube.com/watch?v=bkNMM8uiMww. Brunelleschi already had a mathematical approach to drawing perspective, the setup with the mirror was to actually check that the perspective matched up with what he saw in the real world. By bringing the mirror closer or farther, he could check that the painting and real world aligned.
For more context on this, https://www.youtube.com/watch?v=bkNMM8uiMww. Brunelleschi already had a mathematical approach to drawing perspective, the setup with the mirror was to actually check that the perspective matched up with what he saw in the real world. By bringing the mirror closer or farther, he could check that the painting and real world aligned.