scene:on-click

(scene:on-click v hook)

Calls hook with one argument -- the world point where the click ray meets the plane through the orbit target facing the camera -- every time the view is clicked; nil removes it. A click is a press released without travelling more than a few points, so clicking and orbiting are one gesture and neither needs a modifier. The plane is the one plane a viewer can pick without being told, and it is what makes "click where you see" true from any camera angle; scene:ray is the line itself, for a program that wants a different plane. Part of the scene package, a 3-D viewer for geom solids written in rontolisp over metal and appkit and loaded on first use: macOS (java -jar, the rontolisp binary, or a compiled .class / .jar; never a .wasm), with a display. See the solid modeling guide.

CL-USER> (scene:on-click *v* (lambda (p) (geom:place *marker* :translation p)))
NIL