I need to make a sky for my city. So… I guess I better add one.
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On the computer, it’s possible to draw this box, and then render everything else in the world on top of it, which creates the illusion that the mountains are a huge distance (infinite, actually) away. Now, my skybox isn’t going to be box shaped. Since I’m focusing on making a night time scene, I don’t need the top or bottom. So I’ll make some textures and place them on in side of a shortened tube instead of a cube. So, the viewer of my program is unwittingly wearing a lampshade on their head. Ha ha.
I make a smear of colors and put it on the lampshade.
It’s amazing how you can blur just about any two colors across the view and see it as a horizon. I start with a random warm color, which then fades to a blue, then fades to a very dark blue, and then to black. The specific colors are randomly chosen. I don’t know if it’s supposed to be a sunset or simply city lights bouncing off the atmosphere. It’s a little bright and colorful to be ambient light. But it goes all the way around the horizon, which is something sunsets don’t usually do.
I add some stars.
That’s good, but I’m going to need clouds if I really want to make this lampshade look sky-esque. For some reason, I thought I’d try and generate some puffy clouds fractally. It became apparent very early on that this was a foolhardy approach, but I messed with it a bit longer than I should simply because it was generating such interesting images.
One of the many fractal non-clouds:
Eventually I stop playing around and get back to work. This is very far from my mission parameters. My goal is to sell the scene using simple tricks, and trying to create believable clouds using fractals is the opposite of that. I save the fractal code elsewhere in case I want to play with it again, and devise a simple trick:
I draw my fading circle texture onto the canvas, only I color the circle black. Then I squash it vertically and draw it again, only slightly lighter. The further down the canvas I go, the more I compress my circles vertically. So the circles near the top will be nearly round, but those at the bottom will be nearly a horizontal line. The result:
And now I slap that texture over top of the gradient and the stars:
This is the way to go. I spend some time fussing with the color parameters: Cloud size, opacity, density, the contrast of the lit underside of the cloud, and the degree to which they flatten out as they approach the bottom of the texture. (The horizon, from the user’s point of view.) Unlike the buildings, these parameters aren’t something I can just plug into the random number spewer and create infinite content. Most of these numbers are tradeoffs, and making it look better one way will diminish it in another. Eventually I decide to stop messing with it:
We’re getting close now.
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51 thoughts on “Procedural City, Part 6: Sky”
how big is the code at this stage? still smaller than a non-procedural city? :P
Very nice. I’d mention that what appear to be lights on top of the buildings seem awfully large, and kind of disembodied. And that this is one hell of a densely-packed city so far, but that’s not necessarily a bad thing. You’ve got a believable image here. Under scrutiny, this is still very much a computer-generated cityscape, but at first glance, it’s definitely recognizable for a city at night, and realistic enough that it does take a moment for the eye to realize this isn’t “real”.
This certainly seems to have been a fun project so far, and it goes to show that if what you’re looking for is believable imagery, and you just need fairly generic filler content instead of something hand-crafted, you really can see quite a savings both in artist time and in storage needs by generating some of your content on the fly.
The light atop the “nearest” building is believable, but the other two are a little large as Drew mentioned.
What really blows my mind is that the random dark noise you generated in the lit windows actually fool my eye into thinking I’m seeing silhouettes of people and furnishings. I could swear I see a person in the upper right lit window of the “near” building.
I’m also impressed that the intensity of the color fades out as the scene stretches farther away until the light becomes a dim, hazy blur for the most part. Nice work. Although the green “sunset” throws it off a little bit.
To me, it looks like an underwater city with few spheres of light above the surface of water. Looks good, regardless.
Just a few nitpicks:
I’m not so sure about the clouds and the horizon. The horizon seems to me like it could be quite a bit darker. As it is, it looks like daylight in the distance, as if dusk had suddenly set. Thats not a hard thing to tweak, though.
The clouds look more like ripples on water to me than clouds. They seem to be projecting shadows above/in front of themselves, perhaps you could tweak the degree of darkening? Cites with a great deal of light, as yours has, tend to project that light onto the bottom of clouds. Perhaps the clouds could have a bit of the dominant light color, yellowish?
That effect normally washes out stars, but I would leave those in. It makes the picture more definitively “night” despite a little loss of accuracy.
The fractal clouds look cool. Not very cloud-like though.
I was having trouble seeing the blue meeting the red as a horizon, but with the new clouds in place, it seems a bit easier to see.
I’d agree that the horizon is too light. Most city lights around here are a harsh sulfurous orange-yellow that does often reflect this brightly off the clouds (particularly in winter when it is snowing), but it’s a dark color, not that pale, and it doesn’t graduate out to blue but to a darker and duller shade of orange. So you’d probably be better off with a single color.
Is there any way to make distant objects look a little more hazy (particularly the clouds, which are too clear and too opaque to my mind). This is a good perspective trick because even in clear weather things get hazier with distance because we can only focus our eyes so well. If you could make the red lights on the top of the buildings really bright and sharp when they are close up and then smaller and hazier with distance, that’d go a long way toward reducing some of the perspective “flattening” you have now, as well.
The problem with the red lights is that they’re quite blurred out across many pixels, as though seen through fog…but there’s no noticeable blurring on the other parts of the image that are supposed to be the same distance away. The red lights wind up coming across as giant UFOs off in the far sky.
If, as I’m guessing, they’re supposed to be the aircraft-warning beacons on top of the buildings’ antennas, then they ought to be very bright but very small…each smaller than a window of the corresponding building, so basically a point at this distance. (Either that, or there ought to be a *lot* more fog blurring on the buildings, windows, &c. than there is.)
Aside from that, and the overbright horizon, though…wow. That’s a pretty good cityscape for a few hours’ work. Nifty! :)
(Edit: Ninja’d by Jennifer Snow on the red lights….)
It’s coming along very nicely. A few suggestions:
When I first saw the red lights atop the taller buildings, I had no idea what they were (fairies?). I then realized they were probably supposed to be those low-aircraft warning lights. If so, the light is far too dispersed. Tower lights are very “tight”; a few pixels is all they need to be at that scale.
The clouds are fairly believable, but you shouldn’t be able to see stars through them.
And speaking of stars, in a city that big, with that much light pollution, you’d only be able to see a few dozen of the brightest stars in the sky. With all that cloud cover, and it being only about an hour after sunset (judging from the light on the horizon), you’d see even less.
Still, you’re not trying to make this photo-realistic, and for the time you’ve put into it, I think it’s fantastic.
Edit: Gah. Ninja’d x 2.
Horizon too light, probably too high also. Cloud effect is a good start, but it seems like there’s too many or something.
I agree with Mari that one of the best parts of the code so far is the random noise generated in the windows. It really does make it look like it’s a true building that is populated with furniture, plants, and people.
As far as the lights on the buildings… To much… bloom, I guess would be the word. Even the close light looks like you are seeing just the light through squinted eyes, or a distortion lens of some sort. If we were on the ground looking up at the lights that might be more believable but since we’re fairly close to the same height it seems as though the lights should only have a very slight glow coming from them and be primarily hard points of light. Also, if you are going to have lights there needs to be an obvious structure holding it up, possibly revealed by the glow of the light (which could end up being too complicated as that means you would also want to make the light reflect off of other roof objects as well… but it’s an idea at least).
I preferred the red to blue to black horizon in the second to last image much more than the last horizon which appeared to be much to bright. With the last horizon I feel as though I should be seeing a lot more detail than I am, whereas the second to last feels pretty much spot on.
Also, a short note on the clouds… keep working on them… it seems like in the last image they are just dark streaks across a semi-lit sky. I’m at a loss as for how you would improve them though.
Overall, it’s coming along nicely and I can’t wait to see the final product!
Edit: Doh! Took to long writing all this up… still multiple people saying the same thing is a good thing, right? … Right?
@mark: I think a non-procedural city of the same graphical fidelity would actually be a much smaller code footprint. Instead of a whole lineup of functions to generate buildings, windows, textures, etc…you’d just be loading art assets from a file and rendering them.
edit: I think a quick fix for the red lights on the buildings would be to just make them a lot smaller and stick them on top of a stick/antenna to hint at more structure underneath.
Sometimes those lights look big and blurry like that in photographs because cameras don’t have high dynamic range like human eyes. It looks ok in a still, but I suspect it will look really strange when animated.
I suspect that part of the reason the city feels so crowded is that the buildings are fairly tall right to the edges, which doesn’t really match the behavior of non-huge cities. If you look at the skyline of most cities under 1 million people, they have a relatively concentrated area of tall buildings, which rapidly tapers off as you go out to either side. Only in very large cities are the tall buildings spread out.
The clouds look, to me, like ripples in either water or cloth. The scene was more convincing without them.
That said, everything else is hugely effective.
i request wallpaper-quality images.
especially of the fourth image, with the sky and starfield but no clouds.
Now I have no idea how to do anything like this, so I have no stand to criticize from, however… those clouds look like wrinkles in the canvas of the painted backdrop, ana translight. I have no clue what to suggest, to me the background now looks very fake and made up.
BTW, those fractal clouds looks like something out of Cthulhu!
The clouds do look lit from underneath, but the sky is too blue for dawn or dusk, because the sunlight is entering the atmosphere at it’s maximum angle from vertical and is therefore less blue. I believe refraction should push the color towards red/yellow the closer it is the horizon.
Because of the flatness of the squashed circles, the eye interprets the shadow above as being the actual cloud. Either the shadow needs to get brighter, the cloud get darker, or possible some of both.
I would also shift the horizon line down slightly, but that could just be me
I’m with illiterate up there. Let’s see some high-res images.
That is looking REALLY neat. I like the layered cloud effect. (also in the “sutset-is-too-bright camp” though I don’t think it detracts from the image) I LOVE how the buildings are silhouetted against the background though. Very striking!
This would be really cool if you made a little video flying through the city, around and between buildings.
I think there’s too many windows. I know it’s hard to see the building with less windows, but it just seems rather crowded to me.
Are there no houses in this city? There should be a few areas which have houses and shops and no tower blocks at all… And parks! I know we’re looking at the city-center but still.
I think less windows, maybe not as bright, might look better. Less clouds too. Sometimes less is more…
Just so people stop asking:
Houses, fancy tower-tops, parks, stadiums, shops, etc:
That goes WAY beyond the scope of the project. Yes, cities have that stuff in them, and yes the verisimilitude of this city suffers a bit without them, but those are very complex objects and systems. It was about a week to get the buildings looking right. Each of those things would require almost that much time again to make them look passable. So, no.
The stuff everyone is saying about the sky being too bright & colorful has been noted. The sky & clouds probably need another hour of tweaking. The project is still very much duct tape & cardboard at this point. I want something striking (and something against which the buildings can stand out) but if it looks too cartoon-y it will undo all the more subtle tricks I have going elsewhere in the scene.
I’ll discuss something slightly different here.
If you look up at the night sky in a densely-lit city, you’ll notice that you’d be hard press to see a single star, because of all the light noise from the city. The ones you do see are quite bright and easy to spot.
I’m not looking at a high-resolution image here, but the one with the fractal clouds shows me that the star distribution is fairly high, and the intensity may not be bright enough.
A zoom-in on the panorama view shows me that there’s lots of stars, but none of them are very bright.
one word: wow
And I don’t mean the MMORPG
very much worth the wait to see what your city looks like, especially with a sky.
Those scenes are very cool!
Hot damn the picture of the non clouds is awesome. I kinda want one as my background.
I think this needs some basic fogging.
Very simple technique that would help buildings further away look further away.
Besides that it’s coming along very nicely.
Are you planning on releasing the source code when you’re done playing?
Yep, a very small amount of distance fog is the way to go. Lose the stars (don’t need ’em,) do a much more subtle fading from pink to dark blue, and lose the halo in the red lights. Don’t worry if the red light is a full-bright-red pixel.
This shot shows a really interesting gradient (and no stars!):
There’s too much contrast between the horizon (which seems a bit too high) and the clouds toward the bottom of the texture.
They should grow more translucent, or whatever the Open GL equivalent of that is instead of becoming a series of black stripes on a bright background.
The stripey effect makes it look like something out of an old VGA adventure game or something.
This looks awesome. I’m going to have to dissent here from some of the critics and say that I think the last picture looks quite believable. I think a lot of it depends on what cities you’re used to and where you live. The clouds look very “right” to me because I’m used to dense cloud cover. (The biggish city I’m most familiar with is Seattle.)
The blue clouds make me think of dawn, and it looks realistic to my eye.
The red lights I want to say should be tiny and on the corners instead of big and above the middle if you want them to be air warning lights. As-is, they look most like radio towers.
I think the stars look fine, though I suppose due simply to light pollution they probably shouldn’t be there. But I still think it looks better with the stars.
I have a couple of suggestions to make for your subconscious to turn over. My credentials for offering suggestions: I spent 8 years teaching and doing celestial navigation, therefore I spent a lot of time studying the sky at dusk. Naturally you should feel free to dismiss me like the internet crank I am.
You have said that the sky gradient light problem has been noted. A suggestion to make it more believable: start with darker colors near the horizon sure, but also don’t extend the gradient to black. Very few skies are actually black at night, if you can see stars. And especially if there’s still some light at the horizon. The parameters used in the second from last screenshot are closer to the mark than in the last screenshot in my opinion. The last screenshot changes abruptly from light sky to almost black.
Also, while it’s true that clouds frequently go all the way down to the horizon, the distortion and thickening of atmosphere plus the great distance at the horizon frequently make things blurry there. Also, if there’s an edge to the cloud pattern anywhere within several hundred miles (like a new air mass)that edge will be visible near the horizon. Think about those cloudy days when the sun peeks out just at sunrise for a few orange-golden blissful minutes as it figuratively goes below the level of the cloud ceiling. At any rate, the concrete suggestion here is to have your clouds finish their approach to infinity somewhere between 5-8 degrees above the horizon. Leave it clear below that. True, the buildings might obscure most of the horizon at that level, but I think that this small detail is the kind of thing that will add a bit of verisimilitude.
Finally, I see what people are saying about the ripples and such. I’m not sure how to help with that. You’re the creative genius around here. But in my observation, clouds frequently appear lighter than the night sky because the reflect the light which is otherwise scattered. Both from the dusk at the horizon and the streetlights etc. So you might change the color palette visible in the clouds to reflect this idea. Oy, what a terrible play on words. Sorry.
I would also like to say that this series has been a true delight. Candy for my brain. It may be ‘off subject’ in your eyes, but I’m loving it. Thanks.
Erg. I missed my window to edit or something because I had to put the baby back to sleep. Please change ‘sunrise’ to ‘sunset’ in the previous post.
The buildings all look a bit too uniform in brightness. You might try varying the brightness a bit.
Well, it looks like my original comments about the color of the sky (cloudy city skies look orangey at night) and the problem with the red lights on the building (the colour is bleeding like it’s foggy, but the sky looks clear everywhere else) has already been covered, and responded to. So I’m going to suggest something.
Since skies looks so good as a gradient, and since you are using a cylinder to represent the back ground, you could possibly create a daytime sky and a nighttime sky and trasition between them by simply pasting the entire gradient on the cylinder, with night at the top and day at the bottom, and then moving the cylinder down as day progresses to night. If you tie the background color of the building to the height of the cylinder (ie, grey when the cylinder is high, purply-red sunset colours when the cylinder is medium, and then orangey streetlight color when the cylinder is low) you’ll get the effect of the entire city changing, with just a few variables.
There is at least one problem I see: sunset colours don’t spread through the sky in such a nice orderly fashion, so an actual sunset is unlikely. But there might be a nice effect in there somewhere.
Shamus, do you live in a large city? You can’t see stars there at night, as the light of the skyline is far brighter than what reaches us from the stars. ;)
Now that looks awesome.
If you’re interested in generating clouds procedurally, you might want to take a look at http://freespace.virgin.net/hugo.elias/models/m_clouds.htm
Flaw spotted (In the nicest possible way…):
Just had a thought, the setting of the sun effect doesn’t happen evenly around the horizon. There are some bits that are darker than others.
I can only see one part of the skyline in this, but I assume that since you say this is created as a cylinder, it would have the same effect all the way around.
-Even so, from that one angle that I have seen, it does look pretty good.
Sorry if someone said this before, I couldn’t be bothered to read all the comments as I have got to go and walk my dog
And who says clouds have to look like clouds?
A little artistic license goes a long way.
Besides which, if you put those fractal things in the sky most people will be too busy staring at them to study the rest of the scene too closely. :)
I wonder if you could generate buildings fractally, I suspect some architects have tried it.
Oh, and one other thing, from that cityscape posted above, it looks like you could very easily generate at least some degree of low building zoning on the edges of the city just by scattering lights across the floor.
That’s about it, really, you city looks great otherwise.
But I dare you to find a single reference photo that doesn’t have carlights in the streets below.
Some of the comments in this thread seem inexplicably confrontational or rude. Lists of feature demands, or people questioning if I’ve ever seen a city before like I’m some kind of imbecile. I have no idea what’s inciting this reaction in people, who seem to be offended by the omissions in the reality I’m crafting. Some of the imperfections in the scene aren’t because I’m too stupid to know that sunsets don’t go all the way around the sky, but because I’m not trying to simulate the entire freaking world with perfect fidelity.
I’m not John Carmack. I’m just a guy noodling around with a short-lived hobby project. Let’s keep this in perspective.
I think the city looks awesome and am, like you, confused about the number of nitpicks.
Side note: Reading through the terrain project, I was inspired to take a crack at learning OpenGL. Hope we get to see the source for this as well.
Wow, this looks really awesome. Something about the idea of procedurally generated content really appeals to me, I’d like to learn more about it at some stage.
About all the nitpicking: yeah, I’ve been working on my own creative project (a multiplayer browser game), and the nitpicking and suggestions can get a bit wearying at times. I’m used to it now and appreciate the feedback, but at first I was tempted to ram my keyboard down some people’s throats.
It’s not nice having your ‘baby’ criticised, especially if it’s something you’re doing for fun. But I think the nitpicks are a sign that this project is already pretty awesome, and appears tantalisingly close to perfection. I think everyone is impressed, even those who just posted criticisms.
It’s not that sky is severely flawed. It’s just that, when compared to an otherwise very realistic-looking city, the sky seems a bit off, if you understand what I mean.
Most people have said that the horizon line is too bright. I think the problem is not with the brightness, but that the gradient from warm colours to blue is a bit abrupt.
Other than that, I can’t say anything that hasn’t been said already. I love how this project is coming out, and I enjoy seeing it evolve from just black boxes with tinier white boxes in them to a very believable city.
Oh, and I wonder: are you planning on making some streets wider to suggest avenues and the like? I don’t know anything about programming, but at least it doesn’t sound difficult to implement.
I think this project is totally cool. Reminds me that when I was in high school, my ambition was to be a programmer of awesome 3d games and graphics like this. For some reason I decided against it – something about not wanting to stare at a computer screen all day. The irony is that I went on to study/practice Engineering then Physics and now Statistics, and all of these have involved heavy computing hours and programming. Dang! I’ll just have to live vicariously through people like Shamus – so thanks!
Wow, dude. You’re getting flamed for trying to show people something interesting. I’m digging how this is going so far. I kinda liked the fractal cloud thing – reminded me a bit of the art style of Monkey Island 3. It gives me urges to try build something entirely fractally (spell check says that isn’t a word but I say different). Looking forward to the next step in this project.
Increasingly demanding feedback is, unconsciously, a compliment of your work. It happens because like-minded people see the potential in something you’re doing, see that you’ve caught the spirit of it, and the crowd surges forward to take advantage of the opportunity.
Because geeks tend to be concerned only with ideas and the expression thereof, the feedback is insensitive and selfish.
At least it’s a sign of success.
If you’re surprised by the demanding reaction to a 30-hour hobby program, try devoting 3 years of your life to an old FPS mod. Now that’s a sharp lesson in human ingratitude :P
Shamus, I dunno – those clouds look to me like an inverted sea of water with gently rolling waves.
You may not realize it, but you already knew how to generate clouds years ago. There’s no getting around the fact that clouds are fractal. One can get pretty good clouds using a fractal terrain generator, in which one generates opacities instead of elevations.
One can also do tricks like pre-biasing the landscape elevations (skyscape opacities) to give higher opacity toward the horizon, and even have a nonlinear transparency “waterline” that changes “elevation” toward the horizon.
Of course, you’d then project all this onto your horizon bitmap so you don’t have to worry about rendering the skyscape.
I think you’ll be pleased with the clouds you get using a fractal landscape algorithm. It might be just a few tweaks on your existing past work.
Firstly, I would like to apologise for any anguish, mental or otherwise that I have caused by my previous post. This was not my intention. I guess that I thought since so many other people have been commenting on the project, one more wouldn’t hurt, however since mine was one of the comments specifically picked out in your response, I guess it must have.
I have re-read my original comment above, and while I can appreciate that nitpicking is not a good thing, having thought about it, I think that different people value different parts of a project differently.
To be honest, I don’t understand much programming, but I do know what a sunset looks like. I would have made the buildings blocks with random blobs of light as windows and called it a day with them, but those extra steps you took make it look a lot more interesting.
Likewise, I would have spent more time on the skyline, because I don’t know how to make a car overtake another one, but I do know how a skyline should look.
These are just different flavours of awesomesauce.
It was my impression that you were trying to make something that looks ok from a distance, but wouldn't stand up to close scrutiny. Amongst a city made of buildings which look pretty good, having a skyline which has a literal line all the way around it didn't feel up to the same standard. Since you normally have such attention to detail, I wondered whether looking at still images with a band of sunset had prompted something like my 5th comment in the 2.5 years I have been reading the site.
I really do appreciate that you create posts such as this one, that is after all the reason why I keep coming back to this blog, and it is the only blog that I regularly read.
Over a whole day has passed since your comment and this response. I have actually been thinking about this, and commenting on blogs in general because such things prey on my mind sometimes.
I know a lot of the ‘u r teh suxxors’ type comments come from the fact that the Internet gives you anonymity, and when re-reading my comment, I wondered whether if we were face to face I would have said the same thing.
I came to the conclusion that, yes, I probably would have.
However, I don’t think that I would have got the same sort of reaction (Except the bit about the dog) because if we were talking, then it would have come as part of a discussion, rather than an unexpected stab from the shadows.
As a person who takes such things seriously; does that make it alright? Ultimately, I guess that only you can decide how you feel.
The Internet is an impersonal medium, which is why things like real shops will probably never truly disappear, as the ability to look at the things that you are buying will always be liked, but the art of conversation is being hurt by the fact that people can say whatever they want.
Hmm, my last sentence made me think that you have full editing / deleting facilities for comments, so if they bother you, no one need ever know that these comments ever existed, but that is the subject for another 500 word long comment, so for now I leave you with the following:
You = great
My previous comment (Plus a few comments from others) = great -1
My future comments = 0
Once again, apologies for any annoyance caused, I suggest you name a zombie after me on Left 4 Dead if you feel that bad.
P/S by the way, the dog enjoyed the walk.
Alan: No, the fault is mine. I put this stuff up for everyone to see. It’s quite natural for people to simply say what they’re thinking. That’s the very best sort of feedback, even if it doesn’t feel good. I was just grouchy after a few dozen of them. Perhaps I need to read them in smaller doses.
Please don’t stop giving feedback. :)
Concurring in the general hope that nothing I’ve said came across as demanding; none of it was meant to. It’s just that I don’t know anything about the programming involved here, so all I can do is alternately be awed by the results and nitpick them, without any real sense of which reaction is truly more appropriate at any given moment. :)
Long as I’m in nitpick mode, though, one additional random thought: would it be feasible to take the sky “lampshade” and tilt it a few degrees off vertical? That might be enough to give you a quasi-realistic sunset effect extending just partway around the horizon.
On the other hand, it might be hard to implement for reasons I wouldn’t understand, or it might just not look right. I dunno. This is the Internet; I don’t have to have a clue in order to type stuff here…. ;)
I really appreciate this post. I’ve been looking all over for this! Thank goodness I found it on Bing. You have made my day! Thank you again
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