Collision with a block of the level during a c_move instruction
or physics entity movement. The entity must not be PASSABLE and
value must be 0 or less. On start of the event function,
the event_type variable is set to EVENT_BLOCK, the vector normal is
set to a direction perpendicular to that surface, and the vector bounce is
set to the direction into which the entity would bounce off.
must be smaller or equal to 0.
must not be set.
normal - Surface normal vector bounce - Surface reflection vector