That...thing.

[jefequeso]

Ok, at the bottom of a pool at the beginning of the Temple of Vandora, there's...white, blurry stuff. I swim down and take a closer look, and it seems that it's textured, but it has "motion blur" when you look around. What exactly IS it? Is it a missing texture error that has detailing applied? Or is it supposed to be something weird and "Unreal-y"?

[[]KAOS[]Casey]

It's called a "hall of mirrors" effect

[Skywolf]

that is the result you get when you make something translucant while there is nothing on the other side of the surface. i wonder why it is set to small wavy if you look at the surface properties in unrealED.

[Sly.]

I always thought it was caused by a BSP hole due to the many round and detailled BSP structures in the temple...

Whatever it is, I must say one thing:
EFF, YEAH! I love that HoM effect!
(wanted to dig out that one picture I've made but couldn't find it anymore. )

[Skywolf]

true, you can do some pretty neat stuff with this.

[Hellkeeper]

true, you can do some pretty neat stuff with this.

There used to be a french level-designer that made UT2004 maps entirely made of HOMS with only the edges of the map bright solid colours. Trippy effect and very dangerous for epileptics. As far as I know the guy left UT and his maps were lost.

[jefequeso]

So is it there intentionally? I mean, the spot isn't exactly out of the way. There's even a secret area closer to the surface of the pool. So it's not something that you'd expect to get missed by QA.

[Sly.]

Since nobody expected the Hall of Mirror effect when looking down there and "nobody"/just a few knew it then (from other games), maybe they thought it would be dangerous or something and were afraid to further explore that underwater part?
Well, I for my part was scared, scared of dying by getting too close to what I thought was a nasty, deadly BSP hole.

[Trent Hawkins]

Since nobody expected the Hall of Mirror effect when looking down there and "nobody"/just a few knew it then (from other games), maybe they thought it would be dangerous or something and were afraid to further explore that underwater part?
Well, I for my part was scared, scared of dying by getting too close to what I thought was a nasty, deadly BSP hole.

QFT

ME too...

[Buster]

99.999% of the time HoM is NOT desired. More than likely it was just 'missed' and not cleaned up.

Sometimes the HoM effect is caused by the weird scaling of a texture, as well as a transparent texture (mentioned above). I've found a few of these 'errors' left in different levels, but located in areas not seen by the player.

[Bloodshot]

lol you can add me to that list. Building Quake 1 maps with holes in them as a kid gave me a fear of any HoM effects

[jefequeso]

99.999% of the time HoM is NOT desired. More than likely it was just 'missed' and not cleaned up.

Sometimes the HoM effect is caused by the weird scaling of a texture, as well as a transparent texture (mentioned above). I've found a few of these 'errors' left in different levels, but located in areas not seen by the player.

Yeah, but that's the thing... it's NOT in an out-of-the-way area. It's perfectly obvious to anyone who looks down into the pool... which anyone with sense is going to do, since secrets tend to be underwater in Unreal :3.

Either way, it looks cool.

[GreatEmerald]

Perhaps it was created after QA - the LD decided to add a detail he forgot, and accidentally broke the level when rebuilding it.

[jefequeso]

Perhaps it was created after QA - the LD decided to add a detail he forgot, and accidentally broke the level when rebuilding it.

I suppose that's possible.

One other thing, though. This isn't HoM in the traditional sense, where things stay on the screen in that area indefinitely. It's like all white, and any visuals that pass through it have motion blur... kind of like the sort of blur you see when your character gets hit on the head in a modern game. I only mention this because while playing last night I saw some TRUE HoM appear on a small texture until I got close to it, and it looks nothing like the effect in question.

[Hellkeeper]

One other thing, though.  This isn't HoM in the traditional sense, where things stay on the screen in that area indefinitely.  It's like all white, and any visuals that pass through it have motion blur... kind of like the sort of blur you see when your character gets hit on the head in a modern game.  I only mention this because while playing last night I saw some TRUE HoM appear on a small texture until I got close to it, and it looks nothing like the effect in question.

That's a perfectly normal HOM. Here's why it appears white and there is a "motion blur"-like effect.
The texture is set to small wavy and translucent. Because it is translucent, the texture is brighter than the surrounding area (which, as it happens, is pitch-black). Because the texture is set to Small Wavy, it moves all the time, but this is totally irrelevant.

Now, what a Hall of Mirror does is very simple : there is nothing to display at some place on the screen, so it just displays whatever was at this point on the screen the last time the entire screen was updated, which means you will have precisely whatever was there one frame before. That's why firing a Dispersion Pistol projectile towards a HOM will display a long blue trail from your gun to the impact point : at each point, the only "last" thing there was the blue projectile, so the endless repetition of the blue projectile along its trajectory makes it appear as a long blue trail.

Now what's funny about the "translucent" flag is that whatever is seen through a translucent surface appears brighter.

So in our case we have a set of crippled polygon that make whatever is behind them appear a little bit brighter than they sould otherwise, but there is nothing behind. So by default, the engine will display solid black until something goes there. Yet, this black stuff is seen through a translucent surface, so it's a little bit brighter. Let's say a very dark grey. But the next frame, you will see this dark grey through the translucent surface (since it was the last thing displayed on this part of the screen, it fills the HOM, and the engine adds the translucent surface on top of it). So now we have a slightly brighter grey. But on next frame, the same thing will happen to this new shade of grey. It's as if the engine was stacking up piles and piles of translucent surfaces which act as white filters.

Because the screen is refreshed... Let's say 60 times a second (in my case 120), it takes only a few tenths of a second to go from total black to total white. This can be easily recreated : create a new map, subtract a 256*256*256 cube with no texture, add a small 64*64*64 texture against one of the sides and set all its surfaces to translucent. Activate RealTime Preview and Fake Backdrop : voilà, your own white and foggy HOM.

Now let's compare what we have in the game and in the editor.

In the editor, if you go in the pool and look downwards before activating realtime preview and fake backdrop, you will see the texture. Activate RTP and Fake Backdrop, and you will see two different things depengin on the viewport mode : in Textured mode, all will be white down there, because the floor texture itself will be displayed and because it is itself translucent ! The translucent flag will work its white magic. If you are in Lighting mode when you activate the RTP and Fake Backdrop, you will see complete blackness with patches of colour on the small parts of the texture that receive a little bit of light. Why ? Because translucent polygons that receive no light are completely invisible.

So we have asserted two things : all you need for this effect is a translucent surface. However, you also need this surface to receive some light so that its translucence makes it a whitening lens, and not an invisible surface.

If you go outside the pool, looking down, it will go white no matter what mode you are in, because you have to account for the water-textured sheet that is the surface of the pond, which is in itself translucent. No matter if the texture down there is receives light : as long as it is translucent (thus showing the void behind it) and the water-surface is translucent it visible itself, the whitening effect will be provided by the water-surface sheet.

In game, you have the same effect when looking from outside the pond down the well : the translucent polygon that is the surface of the pond brightens the HOM behind it in a split-second. If you go down the pond, however, another thing comes into play : when you are underwater, there is a whitish filter applied to the entire screen to simulate underwater vision. This means that for each pixel that would be a certain colour, it is now a bit lighter. This is exactly the same as putting an fullbright white translucent surface over the entire screen. The same thing will happen then : all parts wich are HOMs will default to the precedent image and brighten it a little bit, until it reaches the brightest it can achieve : complete snowy polar whiteness.

As for the motion blur itself, it's quite simple really : say you are underwater with your gun. The idle animation of the gun is to move slowly up and down to simulate the player breathing (altough beathing underwater is quite an interesting concept in itself, let's assume for the sake of argument he wears the ScubaGEAR) : the gun will occupy various places on the screen through time : its down position, its up position and all intermediary positions. For each frame, the previous positions of the gun will be whitened a bit until they dissappear and blend into the white void. When you move around the central pillar, the same thing happens : you make the pillar appear on several positions on the screen, and because you have a HOM down there, you can see all the positions it occupied, but all the positions it no longer occupies are progressively being washed down into the white abyss.

So there you have it : a completely normal HOM, but it is made white by both the translucent surface you see it through when outside the pond and the white filter applied to the screen when underwater in the game. The fact that it is white in all cases gives the impression it is a quality inherent to the HOM and that this HOM is special, but it is in fact totally dependent on other factors. Like lighting : subtract a 256*256*256 square, set its surfaces to translucent, but add a completely red light in the room (brightness 255; Hue 0; Saturation 0). Activate RealTime Preview and Fake Backdrop : complete red communistness surrounds you instead of the white nothing. Repeat with blue and green : this is the same. What matters is the colour the translucent surfaces are lit with. Remember however that if the colour is not solid colour (like 0 saturation = complete red), but slighly washed down (even a measly 10 saturation) the constant updating will eventually turn the whole screen white, just needing a lot more time, because the brightening of each and every pixel will be very small each frame. This can be easily demonstrated in the map itself : above the well is a light that gives a whitish light to the general area : make it toally purple, and from outside, our beloved HOM will appear as a violet mess. Dive into the water, however, and the white filter for underwater vision makes it white almost instantly.

[jefequeso]

One other thing, though.  This isn't HoM in the traditional sense, where things stay on the screen in that area indefinitely.  It's like all white, and any visuals that pass through it have motion blur... kind of like the sort of blur you see when your character gets hit on the head in a modern game.  I only mention this because while playing last night I saw some TRUE HoM appear on a small texture until I got close to it, and it looks nothing like the effect in question.

That's a perfectly normal HOM. Here's why it appears white and there is a "motion blur"-like effect.
The texture is set to small wavy and translucent. Because it is translucent, the texture is brighter than the surrounding area (which, as it happens, is pitch-black). Because the texture is set to Small Wavy, it moves all the time, but this is totally irrelevant.

Now, what a Hall of Mirror does is very simple : there is nothing to display at some place on the screen, so it just displays whatever was at this point on the screen the last time the entire screen was updated, which means you will have precisely whatever was there one frame before. That's why firing a Dispersion Pistol projectile towards a HOM will display a long blue trail from your gun to the impact point : at each point, the only "last" thing there was the blue projectile, so the endless repetition of the blue projectile along its trajectory makes it appear as a long blue trail.

Now what's funny about the "translucent" flag is that whatever is seen through a translucent surface appears brighter.

So in our case we have a set of crippled polygon that make whatever is behind them appear a little bit brighter than they sould otherwise, but there is nothing behind. So by default, the engine will display solid black until something goes there. Yet, this black stuff is seen through a translucent surface, so it's a little bit brighter. Let's say a very dark grey. But the next frame, you will see this dark grey through the translucent surface (since it was the last thing displayed on this part of the screen, it fills the HOM, and the engine adds the translucent surface on top of it). So now we have a slightly brighter grey. But on next frame, the same thing will happen to this new shade of grey. It's as if the engine was stacking up piles and piles of translucent surfaces which act as white filters.

Because the screen is refreshed... Let's say 60 times a second (in my case 120), it takes only a few tenths of a second to go from total black to total white. This can be easily recreated : create a new map, subtract a 256*256*256 cube with no texture, add a small 64*64*64 texture against one of the sides and set all its surfaces to translucent. Activate RealTime Preview and Fake Backdrop : voilà, your own white and foggy HOM.

Now let's compare what we have in the game and in the editor.

In the editor, if you go in the pool and look downwards before activating realtime preview and fake backdrop, you will see the texture. Activate RTP and Fake Backdrop, and you will see two different things depengin on the viewport mode : in Textured mode, all will be white down there, because the floor texture itself will be displayed and because it is itself translucent ! The translucent flag will work its white magic. If you are in Lighting mode when you activate the RTP and Fake Backdrop, you will see complete blackness with patches of colour on the small parts of the texture that receive a little bit of light. Why ? Because translucent polygons that receive no light are completely invisible.

So we have asserted two things : all you need for this effect is a translucent surface. However, you also need this surface to receive some light so that its translucence makes it a whitening lens, and not an invisible surface.

If you go outside the pool, looking down, it will go white no matter what mode you are in, because you have to account for the water-textured sheet that is the surface of the pond, which is in itself translucent. No matter if the texture down there is receives light : as long as it is translucent (thus showing the void behind it) and the water-surface is translucent it visible itself, the whitening effect will be provided by the water-surface sheet.

In game, you have the same effect when looking from outside the pond down the well : the translucent polygon that is the surface of the pond brightens the HOM behind it in a split-second. If you go down the pond, however, another thing comes into play : when you are underwater, there is a whitish filter applied to the entire screen to simulate underwater vision. This means that for each pixel that would be a certain colour, it is now a bit lighter. This is exactly the same as putting an fullbright white translucent surface over the entire screen. The same thing will happen then : all parts wich are HOMs will default to the precedent image and brighten it a little bit, until it reaches the brightest it can achieve : complete snowy polar whiteness.

As for the motion blur itself, it's quite simple really : say you are underwater with your gun. The idle animation of the gun is to move slowly up and down to simulate the player breathing (altough beathing underwater is quite an interesting concept in itself, let's assume for the sake of argument he wears the ScubaGEAR) : the gun will occupy various places on the screen through time : its down position, its up position and all intermediary positions. For each frame, the previous positions of the gun will be whitened a bit until they dissappear and blend into the white void. When you move around the central pillar, the same thing happens : you make the pillar appear on several positions on the screen, and because you have a HOM down there, you can see all the positions it occupied, but all the positions it no longer occupies are progressively being washed down into the white abyss.

So there you have it : a completely normal HOM, but it is made white by both the translucent surface you see it through when outside the pond and the white filter applied to the screen when underwater in the game. The fact that it is white in all cases gives the impression it is a quality inherent to the HOM and that this HOM is special, but it is in fact totally dependent on other factors. Like lighting : subtract a 256*256*256 square, set its surfaces to translucent, but add a completely red light in the room (brightness 255; Hue 0; Saturation 0). Activate RealTime Preview and Fake Backdrop : complete red communistness surrounds you instead of the white nothing. Repeat with blue and green : this is the same. What matters is the colour the translucent surfaces are lit with. Remember however that if the colour is not solid colour (like 0 saturation = complete red), but slighly washed down (even a measly 10 saturation) the constant updating will eventually turn the whole screen white, just needing a lot more time, because the brightening of each and every pixel will be very small each frame. This can be easily demonstrated in the map itself : above the well is a light that gives a whitish light to the general area : make it toally purple, and from outside, our beloved HOM will appear as a violet mess. Dive into the water, however, and the white filter for underwater vision makes it white almost instantly.

Ahhhhhhh. That explains it then.

Of course, it still looks cool IMO. Even if it isn't intentional.