Hallucination - how good is the processing power in our brains?

I guess I never had a hallucination. But I always wondered how it actually works with regards to the processing power and visual accuracy?
I'm not sure how graphically correct intense hallucinations can be, but sometimes in movies it is depicted as very accurate.
Like someone on drugs seeing monkeys running around the room etc.

Just from a pure processing point of view:
Imagine some 3D-creator had to make such a scene. Monkeys running/climbing around an existing room filled with furniture.
That's some intensive work that had to be done.

- Creating the monkey model
- Texturing the monkey model
- The shaders
- The lighting and illumination
- The animation
...

Our brain is able to create such a scene, not just a single image, but an animated scene out of thin air? On the fly? So realistic that the person having the hallucination actually thinks what they are seing is real? Just for instance, how does the brain know how to cast visually correct shadows of some non-existing but even animated thing moving around a real environment?

Am I overthinking this?
Are hallucinations actually not that good? More like dreams, very diffuse visually? And the person having hallucination is just not able to notice all the graphical inconsistencies?

Or is it visually so good that you can't notice the difference?

via International Skeptics Forum https://ift.tt/3aJMwTW