Real-Time 3D Graphics with WebGL 2 - Second Edition

Picker Architecture

As you may have noticed, every picker state has a callback function associated with it. The following process outlines what happens in the Picker class when the user clicks the mouse on the canvas, drags it, and releases it:

State	Callback
Picker searches for a hit	hitPropertyCallback(object): This callback informs the picker about which object property to use to make the comparison with the retrieved color from the offscreen framebuffer.
User drags mouse in picking mode	moveCallback(dx, dy): When the picking mode is activated (by having picked at least one object), this callback allows us to move the objects in the picking list (hits). This list is maintained internally by the Picker class.
Remove hit from picking ...