useCapture() gives the game a camera of its own. capture({ region, hide, width, height }) resolves on the next frame with the photo: its pixels, as the player sees them, and boxes, what came out in it, each with how much of it is in (seen, from 0 to 1) and where.
region is a rectangle of the screen or a box: here the viewfinder, measured even though the viewfinder itself is left out with hide, along with the HUD. The print in the corner is a picture painted in code (createPixels, createPixelTexture) that each photo is copied into before updatePixelTexture.
Click the preview first so it hears the keyboard. The arrows move the viewfinder and space takes the photo: the score says how much of the bird you caught.