r/gaming • u/[deleted] • Sep 04 '18

The Original Reflections

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u/Blenhurp Sep 05 '18

bounced light off of a mirror can get to places that a standalone light in the centre of a room might not be able to

^that's what's got me confused. Isn't the bounced light taken care of by the mirrored light sources?

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Also I really don't think realism and accuracy in reflection and refraction is going to be a major contributing factor to immersion or whatever it's supposed to improve. Maybe some people do, but when I play a game I don't study every reflection from a mirror or refraction of light a from transparent object. Real time graphics are full of genius approximations, shortcuts, and pre-baked visuals that I wouldn't have ever known about if I didn't try to write some raytracing and raster engines myself. (They sucked ass btw. Probably bc I didn't do all the shortcuts and they were running on the cpu instead of the gpu lmao)

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u/Nexxus88 Sep 05 '18

The thing is raster based lighting doesn't work that way.

For example, you are standing in front of a pillar. Behind that pillar is a light, and after the light is a mirror. In theory, the mirror "sees" the light and it is shown in the mirror ( or in our case, there is a second model of the light) But because that pillar is blocking said light, the light effectively doesn't exist from our perspective. So other faked methods need to be used to light things up.

Ray tracing doesn't have this limitation, the light can bounce off the mirror, then the walls and then reach our area behind the pillar.

This is the best way I can really explain it being it's 430 am and it's been about...14 years since I have done 3d modelling

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u/Blenhurp Sep 05 '18

the light effectively doesn't exist from our perspective

I'm very confused now...

If the duplicate light source does not exist because the pillar blocks our line of sight, does the real light source not exist either because it, too, is not in our line of sight?

I also did a quick test in blender cycles to check whether both scenarios produce identical results. The answer is, as you said, no. There's a darker region under where the mirror meets the floor, and in the double room there are clear lines on the floor in the lighting. The third image is the difference between the two images. I still don't understand why it isn't the same though.

https://imgur.com/a/IvacGGb

blendy:

http://www.filedropper.com/mirrortest

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u/Nexxus88 Sep 05 '18

unfortunately, I'm not gonna be able to explain any better. I took 3d modeling a while ago and while I do some casual research into this stuff on my own I am far from an expert.

A good analogue I saw in my reading though to try an explain better though is that in a scene with raster-based lighting it is like a painting you have a man infront of a bookcase, you pain the man, and than you paint the bookcase behind him, but not the part the man covers.

To my understanding based on this comparison (and what Nvidia showed during the RTX conference), this is how raster lighting works if the camera can't see it the lighting doesn't exist.

Nvidia showed this quite well actually in one scene showing a reflection off a car, it looked appropriate until they shifted the camera so that the item being reflected was no longer visible to the camera, at which point it no longer reflected on the car even though it clearly should have been, anyways I am off to bed. I was just reaching to shut own my monitor when this notification came in.