Each shape is rendered into an off-screen Framebuffer with its id encoded as
a color. Move your pointer over the canvas — a one-pixel readback under
the cursor identifies the shape with no CPU ray-casting and no scene graph.
id 4 · 0.0 ms
Framebuffer · readPixels
The id buffer re-renders only when the scene changes; picking is just
readPixels(x, y, 1, 1) against it. The same pattern scales to thousands of
objects — ids are cheap. API reference:
Framebuffer readback.