isVisible() default state is true about maratis HOT 4 OPEN

isVisible just returns the state of m_isVisible (usually updated by the 
updateVisibility function)
use isActive first to skip deactivated objects

isVisible() is related to frustum culling (inside the camera view), it doesn't 
take account of walls or other objects occlusion. It is only used during the 
current point of view rendering because it is view dependent.

For a more precise visibility test you can send a ray using the physics context 
or using MMeshTools raytracing (slower).

[deleted comment]

"use isActive first to skip deactivated objects"

I was expecting the isVisible function to perform this check before returning 
the visibility test.

Currently, even if the deactivated object is outside of the point of view, true 
is returned.

both functions don't execute any code, they just return a variable (m_isActive 
and m_isVisible) so both are fast