Second Life Forums Archive - question on reflections

paulie Femto

Into the dark

Join date: 13 Sep 2003

Posts: 1,098

12-14-2005 18:01

I'm standing with the sun at my back, looking at a stream in front of me. I dont see any reflection of the sun (above and behind me) in the stream. However, if I cross the stream and look at the water from the opposite bank, I see a reflection of the sun in the water.

My question: is this physically (realworld) correct? I suspect it is not. Shouldn't the sun be reflected in the water no matter which side of the stream I am standing on?

I suspect that the "reflection" only shows up if the "sun" is being drawn and since the sun is not being drawn (for me) when it is behind me, I get no reflection.

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Zapoteth Zaius

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Join date: 14 Feb 2004

Posts: 5,634

12-14-2005 18:14

Lol this is a world where objects and avatar clothing ripple along with ripple water if you stand in front of it.. I doubt its correct..

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Siggy Romulus

DILLIGAF

Join date: 22 Sep 2003

Posts: 5,711

12-14-2005 22:57

waves go in one direction too - from my home the waves roll out from the shore..

Still - its a frickin neat looking effect - and I'm not gonna nitpick - certainly better than it was - I didn't see the old ripple effect (piss poor vid card at the time) - so I can't compare.

Definately worth the handfull of of fps.

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Beatfox Xevious

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12-14-2005 22:59

Actually, Paulie, that is entirely correct.

Imagine that the water is actually the divider between our world and the "mirror world". Everything that exists above the waterline has a mirrored twin below the waterline. Positionwise, twins always share the same latitude and longitude; they only differ in altitude.

This means that if the "normal" sun is above and behind you, its mirror-world twin is below and behind you. There's no way you could see either one without turning around.

Likewise, if the "normal" sun is above and in front of you, its twin is below and in front of you... floating in the water for you to see.

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paulie Femto

Into the dark

Join date: 13 Sep 2003

Posts: 1,098

...

12-16-2005 17:42

interesting... and it sounds right. So would the solution be for SL to implement reflection maps?

Anyone else care to respond?

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Beatfox Xevious

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12-17-2005 23:56

From: paulie Femto

interesting... and it sounds right. So would the solution be for SL to implement reflection maps?

Er... solution to what? I'm not sure what the problem is.

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Frans Charming

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Join date: 28 Jan 2005

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12-18-2005 03:44

From: Beatfox Xevious

Actually, Paulie, that is entirely correct.

Imagine that the water is actually the divider between our world and the "mirror world". Everything that exists above the waterline has a mirrored twin below the waterline. Positionwise, twins always share the same latitude and longitude; they only differ in altitude.

This means that if the "normal" sun is above and behind you, its mirror-world twin is below and behind you. There's no way you could see either one without turning around.

Likewise, if the "normal" sun is above and in front of you, its twin is below and in front of you... floating in the water for you to see.

That is only true for completly flat water, but we are seeing waves wich in reality would have to cause some reflection of the sun back to us.

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Beatfox Xevious

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12-18-2005 14:42

From: Frans Charming

That is only true for completly flat water, but we are seeing waves wich in reality would have to cause some reflection of the sun back to us.

From what I can see, the ripples (I hesitate to call them full-on waves) are reflecting some sunlight back the other way. But keep in mind this only occurs according to the "depth" of the ripples. SL's ripples aren't exactly deep.

Now, the question of whether they should be deeper is a whole other can of worms...

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Runitai Linden

Linden Lab Employee

Join date: 29 Aug 2005

Posts: 52

12-18-2005 17:04

There really is no sun reflection in the ripple water. It's really just a very hard specular highlight, which looks an awful lot like a reflection. It's computed by taking the vector from the wave to your eye, reflecting it off the wave, doing a dot product off the vector from the wave to the sun, and then blasting everything to some ridiculous exponent somewhere between 16 and 512, I think.

You can see all the math in app_settings/waterF.cg

The reason I went to all that trouble was because the sun isn't in the reflection map. Second Life has one reflection map which gets put on everything, so it has to stay generic. Putting the sun in the reflection map would look wierd for shiny things that are inside. The reason you don't get the shine of the sun in the water looking away from the water is because none of the waves are steep enough to reflect back the sun. This is more or less in-line with reality.

Schwanson Schlegel

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Join date: 15 Nov 2003

Posts: 2,721

12-18-2005 17:12

Thanks for clearing that up, Runitai.

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Beatfox Xevious

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12-18-2005 17:42

Yes, thank you Runitai! That's pretty much a technicalized version of what I'd been trying to say. I knew the water wasn't really reflecting the "actual" SL sun, but I just wanted to keep everything simplified for the topic at hand.

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paulie Femto

Into the dark

Join date: 13 Sep 2003

Posts: 1,098

materials system

12-18-2005 20:21

When we change to a "materials" based texture system, here's hoping we can apply some decent gloss maps, reflection maps, specular maps, cube maps, displacement or parallax maps, etc, etc to "water."

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Argent Stonecutter

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Join date: 20 Sep 2005

Posts: 20,263

12-18-2005 21:42

From: Runitai Linden

There really is no sun reflection in the ripple water. It's really just a very hard specular highlight, which looks an awful lot like a reflection. It's computed by taking the vector from the wave to your eye, reflecting it off the wave, doing a dot product off the vector from the wave to the sun, and then blasting everything to some ridiculous exponent somewhere between 16 and 512, I think.

That sounds like a raytraced reflection to me.

question on reflections
paulie Femto Into the dark Join date: 13 Sep 2003 Posts: 1,098	12-14-2005 18:01 I'm standing with the sun at my back, looking at a stream in front of me. I dont see any reflection of the sun (above and behind me) in the stream. However, if I cross the stream and look at the water from the opposite bank, I see a reflection of the sun in the water. My question: is this physically (realworld) correct? I suspect it is not. Shouldn't the sun be reflected in the water no matter which side of the stream I am standing on? I suspect that the "reflection" only shows up if the "sun" is being drawn and since the sun is not being drawn (for me) when it is behind me, I get no reflection. _____________________ REUTERS on SL: "Thirty-five thousand people wearing their psyches on the outside and all the attendant unfettered freakishness that brings."
Zapoteth Zaius Is back Join date: 14 Feb 2004 Posts: 5,634	12-14-2005 18:14 Lol this is a world where objects and avatar clothing ripple along with ripple water if you stand in front of it.. I doubt its correct.. _____________________ I have the right to remain silent. Anything I say will be misquoted and used against me. --------------- Zapoteth Designs, Temotu (100,50) ---------------
Siggy Romulus DILLIGAF Join date: 22 Sep 2003 Posts: 5,711	12-14-2005 22:57 waves go in one direction too - from my home the waves roll out from the shore.. Still - its a frickin neat looking effect - and I'm not gonna nitpick - certainly better than it was - I didn't see the old ripple effect (piss poor vid card at the time) - so I can't compare. Definately worth the handfull of of fps. _____________________ The Second Life forums are living proof as to why it's illegal for people to have sex with farm animals. From: Jesse Linden I, for one, am highly un-helped by this thread
Beatfox Xevious is THOUSANDS OF PEOPLE Join date: 1 Jun 2004 Posts: 879	12-14-2005 22:59 Actually, Paulie, that is entirely correct. Imagine that the water is actually the divider between our world and the "mirror world". Everything that exists above the waterline has a mirrored twin below the waterline. Positionwise, twins always share the same latitude and longitude; they only differ in altitude. This means that if the "normal" sun is above and behind you, its mirror-world twin is below and behind you. There's no way you could see either one without turning around. Likewise, if the "normal" sun is above and in front of you, its twin is below and in front of you... floating in the water for you to see. _____________________ My Beatworks: Zephyr Chimes wind chimes, the KanaMaster Japanese kana tutor, and the FREE Invisibility Prim Public. Look for them at the Luskwood General Store in Lusk (144, 165). "You have been frozen. You cannot move or chat. A pony will contact you via instant message (IM)." - mysterious system message I received after making off with Pony Linden
paulie Femto Into the dark Join date: 13 Sep 2003 Posts: 1,098	... 12-16-2005 17:42 interesting... and it sounds right. So would the solution be for SL to implement reflection maps? Anyone else care to respond? _____________________ REUTERS on SL: "Thirty-five thousand people wearing their psyches on the outside and all the attendant unfettered freakishness that brings."
Beatfox Xevious is THOUSANDS OF PEOPLE Join date: 1 Jun 2004 Posts: 879	12-17-2005 23:56 From: paulie Femto interesting... and it sounds right. So would the solution be for SL to implement reflection maps? Er... solution to what? I'm not sure what the problem is. _____________________ My Beatworks: Zephyr Chimes wind chimes, the KanaMaster Japanese kana tutor, and the FREE Invisibility Prim Public. Look for them at the Luskwood General Store in Lusk (144, 165). "You have been frozen. You cannot move or chat. A pony will contact you via instant message (IM)." - mysterious system message I received after making off with Pony Linden
Frans Charming You only need one Frans Join date: 28 Jan 2005 Posts: 1,847	12-18-2005 03:44 From: Beatfox Xevious Actually, Paulie, that is entirely correct. Imagine that the water is actually the divider between our world and the "mirror world". Everything that exists above the waterline has a mirrored twin below the waterline. Positionwise, twins always share the same latitude and longitude; they only differ in altitude. This means that if the "normal" sun is above and behind you, its mirror-world twin is below and behind you. There's no way you could see either one without turning around. Likewise, if the "normal" sun is above and in front of you, its twin is below and in front of you... floating in the water for you to see. That is only true for completly flat water, but we are seeing waves wich in reality would have to cause some reflection of the sun back to us. _____________________
Beatfox Xevious is THOUSANDS OF PEOPLE Join date: 1 Jun 2004 Posts: 879	12-18-2005 14:42 From: Frans Charming That is only true for completly flat water, but we are seeing waves wich in reality would have to cause some reflection of the sun back to us. From what I can see, the ripples (I hesitate to call them full-on waves) are reflecting some sunlight back the other way. But keep in mind this only occurs according to the "depth" of the ripples. SL's ripples aren't exactly deep. Now, the question of whether they should be deeper is a whole other can of worms... _____________________ My Beatworks: Zephyr Chimes wind chimes, the KanaMaster Japanese kana tutor, and the FREE Invisibility Prim Public. Look for them at the Luskwood General Store in Lusk (144, 165). "You have been frozen. You cannot move or chat. A pony will contact you via instant message (IM)." - mysterious system message I received after making off with Pony Linden
Runitai Linden Linden Lab Employee Join date: 29 Aug 2005 Posts: 52	12-18-2005 17:04 There really is no sun reflection in the ripple water. It's really just a very hard specular highlight, which looks an awful lot like a reflection. It's computed by taking the vector from the wave to your eye, reflecting it off the wave, doing a dot product off the vector from the wave to the sun, and then blasting everything to some ridiculous exponent somewhere between 16 and 512, I think. You can see all the math in app_settings/waterF.cg The reason I went to all that trouble was because the sun isn't in the reflection map. Second Life has one reflection map which gets put on everything, so it has to stay generic. Putting the sun in the reflection map would look wierd for shiny things that are inside. The reason you don't get the shine of the sun in the water looking away from the water is because none of the waves are steep enough to reflect back the sun. This is more or less in-line with reality.
Schwanson Schlegel SL's Tokin' Villain Join date: 15 Nov 2003 Posts: 2,721	12-18-2005 17:12 Thanks for clearing that up, Runitai. _____________________
Beatfox Xevious is THOUSANDS OF PEOPLE Join date: 1 Jun 2004 Posts: 879	12-18-2005 17:42 Yes, thank you Runitai! That's pretty much a technicalized version of what I'd been trying to say. I knew the water wasn't really reflecting the "actual" SL sun, but I just wanted to keep everything simplified for the topic at hand. _____________________ My Beatworks: Zephyr Chimes wind chimes, the KanaMaster Japanese kana tutor, and the FREE Invisibility Prim Public. Look for them at the Luskwood General Store in Lusk (144, 165). "You have been frozen. You cannot move or chat. A pony will contact you via instant message (IM)." - mysterious system message I received after making off with Pony Linden
paulie Femto Into the dark Join date: 13 Sep 2003 Posts: 1,098	materials system 12-18-2005 20:21 When we change to a "materials" based texture system, here's hoping we can apply some decent gloss maps, reflection maps, specular maps, cube maps, displacement or parallax maps, etc, etc to "water." _____________________ REUTERS on SL: "Thirty-five thousand people wearing their psyches on the outside and all the attendant unfettered freakishness that brings."
Argent Stonecutter Emergency Mustelid Join date: 20 Sep 2005 Posts: 20,263	12-18-2005 21:42 From: Runitai Linden There really is no sun reflection in the ripple water. It's really just a very hard specular highlight, which looks an awful lot like a reflection. It's computed by taking the vector from the wave to your eye, reflecting it off the wave, doing a dot product off the vector from the wave to the sun, and then blasting everything to some ridiculous exponent somewhere between 16 and 512, I think. That sounds like a raytraced reflection to me.

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