common and potential mistakes:
 - forget to reset homogeneous coordinates correctly (points: 1, vectors: 0)
 - normalize some vectors when you shouldn't (e.g., ray directions)
 - forget to normalize vectors when you should (e.g., normals)
 - forget to update inverse transformation matrices (e.g., _imat)
 - forget to update inner matrices with updateTransform(), or update at a wrong time
 - incorrectly marking ray tracing as hit/miss
 - recursively ray-trace at the same point (of the same object)
 - use exact equality for floating-point numbers (precision errors)

debugging tips:
 - to debug or visualize normal vectors, you may use their coordinates as actual object colors. In this case, you may have to adjust value ranges from [-1,1] to [0,1]. Then the colors should vary smoothly on smooth surfaces.

Suggested controls for adding/removing objects:
 - to add an object, press 'n' followed by a number, or 'n' again to cancel adding
 - to remove the selected object, press 'm'
 - print to the console informative messages for how to add/remove objects

Report any bug

inverse matrix already computed when checking ray-object intersection

bullets: Release (146s) vs Debug (557s)