Showing posts with label lighting. Show all posts
Showing posts with label lighting. Show all posts

Saturday, 27 November 2010

Coloured light in Proun

(At Ronimo Games, the Dutch game developer where I am lead programmer, we are currently looking for a coder with experience on the 360 and/or PS3. Interested? Have a look here for more information!)

Last weak I talked a bit about the technical side of lighting in Proun. This week, let's have a look at the more artistic side: the strange light colours I chose for each level.

A very common lighting setup among 3D artists is to let the sky emit a soft blue light, and the sun a bright yellow. This of course makes sense, since these are the colours that the sun and the sky have in the real world.

The fun of having these different colours for the skylight and the sun, is that the sun's shadows become a subtle blue. Brightly lit spots, on the other hand, may become slightly yellow. This fits what my highschool art teacher used to tell me: never paint a shadow with black, always add colour. (Of course, I didn't really understand her at the time...) Since I like this setup, I used it for Proun's first track.

For the second track, I wanted to use a totally different colour palette. Now I am not very knowledgeable in colour theory, but I did notice that yellow and blue are exactly opposite colours. So again I chose opposite colours and after a lot of experimenting with the colour scheme that I had in mind, I came up with a cyan/blue sun and an orange skylight. That is one really weird lighting setup, but I do think it looks good:

The third track is probably the weirdest. A greenish/blueish sun is combined with a pinkish skylight. I think this mainly proves that as long as two colours are chosen that work well together, the colours can be as crazy as you like. So no need to go for the standard lighting setups any more!

So, as these images show, the bright colours of Proun's objects are combined with much more subtle colour effects from the lights. Having just the bright colours worked perfectly well for many works by Kandinsky and Mondriaan, but I think in Proun's case, the subtle colours and shades that the lights add are what really make the graphics shine.

Saturday, 20 November 2010

Lighting in Proun

Proun is getting a lot of very positive responses to how it looks. Most people seem to think that the depth of field blur is the core reason for this, but the game still looks pretty good when that is turned off. What really makes the biggest difference, is the careful lighting.

Since most of Proun's environments are static, the lighting is calculated beforehand and stored in lightmaps. Calculating lighting beforehand is called baking. Baking should not be confused with cooking, which stands for saving memory directly to disc (this is used to speed-up loading times, because you don't have to parse cooked data). Interestingly, I have heard rumours that the terms baking and cooking are also sometimes used for certain algorithms that are used in kitchens, but I don't know anything about that.

Lightmaps take up a lot of space (one third of Proun's total size), but they have some big benefits. Because lighting is calculated beforehand on the developer's computer, it doesn't matter if it takes a lot of time. This means that much more complex lighting can be used than when it is calculated in real-time. In Proun, I use this a lot. I think calculating all the lightmaps for just the second track cost my laptop about 30 hours!

The further a shadow is from the object that casts it, the blurrier is gets, especially if the light source is large. Lights that cast shadows that get blurrier with distance are usually called area lights. In practice, it is hardly ever possible to calculate this in real-time, so most games have either fully sharp shadows (as if the light source is infinitely small), or a fixed blur that ignores distance.

(On a sidenote: as soon as Proun is finished, I am going to implement a technique that I have come up with that makes it possible to render real-time area light shadows in games with a Diablo-like perspective.)

In the real world, a lot of light does not come directly from the sun: part of the light is scattered by the atmosphere and comes from all directions. Such light from all directions is called skylight. Skylight makes shadows less deep and add a lot of subtle shadow effects to the world.

Objects reflect light. So if light falls on a red object, then this object will reflect a little bit of red light onto the objects around it. This is called global illumination. This is a very subtle effect, but because of Proun's bright colours it is clearly visible in a couple of places.

All of these things are only possible because in Proun, lights don't move and almost all objects are static. I could not have used lightmaps otherwise. The levels are also small enough to store high quality lightmaps of all objects.

The things I discussed here today are pretty technical. In a future blogpost I will talk a bit about the artistic side of Proun's lighting: crazy light colours.

Saturday, 13 November 2010

Sun rays

Writing shaders is one of the things that I enjoy most in making games. Kind of surprising, really, because generally I dislike doing low-level coding and optimisation. Shaders are among the worst in terms of dirty hacks and hardware specific code. So why do I enjoy writing them, then? I think shaders attract me because of this: they are so limited, that science and optics become totally useless. The way real light works is so much more complex than what you can do in a shader, that you need to just make something up that kind of looks similar, although it is often totally unrealistic. Physically, most shaders are utter nonsense. So instead of being all about knowledge and math, shaders centre on creativity and experimenting. Now that's fun! (At least, to a special kind of people, also known as Joosts.)

One of the nicest examples of creativity in shaders is how light shafts are rendered in games. Light shafts are also known as god rays, volume light, sun rays or Jacob's ladders. They are what you see when a light shines through misty air. The microscopic particles in the air are lit and become visible.

Rendering volume light realistically takes a lot of computation time. You need to trace rays through air, take into account the density of the mist, and for a large number of points in the air you need to calculate whether the particles there are illuminated by your light. This includes doing shadow calculations for each of these points in the air. This is way too complex to do well in real-time.

So, some clever programmer somewhere (not me) came up with a trick that looks great and is a whole lot simpler to do. The idea is really simple: you just walk over the image from the pixel towards the sun, and look how much light there is in the image.

Click here for the original article about this technique, which is also the source of these images.

Things like volume, fog density and shadow are completely ignored. There is hardly any relation between this technique and how real volume light works, but somehow it looks very similar and really convincing. Games like Far Cry 2 and Crysis use it to create beautiful lighting effects through the leaves.

There are some limitations to this technique, though. Most importantly, it only works if the light source itself is actually in view. For example, using this technique, it is impossible to render the effect of a flashlight that is pointing away from the viewer.

Rendering light shafts this way not only looks awesome; it is also one of the most beautiful, simple and ingenious shader techniques I know of. Since I like this effect so much, I couldn't help myself but add it to Proun's third track. The track's graphics are far from final, but the light shafts are there. The little video at the beginning of this post shows how dynamic the effect looks in motion.

Saturday, 18 September 2010

Overbright colours, blur and faking it

Last week I talked about depth of field blur, a very obvious and visible graphical effect in Proun. Now let's look at one that is a lot more subtle: blurred HDRI.

In computer games, colours are usually stored with values from 0 to 255, with 0 being black and 255 being white. Few people realise that this introduces some limitations.

The problem is that when an object is lit by a very bright light, its colour might actually have brightness 400 instead of 255. To solve this, graphics cards usually just round this down to 255, since your monitor or television cannot show anything brighter than that anyway.

But what happens when we blur such a bright area with its dark surroundings? Without blur, a white square with value 255 looks the same as one with value 400, because monitors cannot show anything brighter than 255. However, when blurred, there is a big difference, as you can see in this image:

As you can see here, when blurred, really bright objects should look like they grow: they overshine the area around them. Dark details around overbright objects can even totally disappear this way. In Proun, this can be seen clearly in the white boxes at the start of the first track: in the distance, their black outlines disappear. I love to look at this effect:

Allowing colours to go beyond 255 is called HDRI (High Dynamic Range Lighting). On the graphics hardware, to make this happen, you can simply turn this on. (In technical terms: switch the render buffer from 8 bit fixed point per colour channel to 16 bit floating point).

However, that is pretty slow, especially on slightly older videocards. So to save a lot of performance in Proun, I faked the HDRI in a pretty easy way. Objects are simply rendered half as bright as they really are and then after the depth of field blur has been applied, the pixels are made twice as bright again. The end result looks just like HDRI, but without the slowness.

There are two drawbacks to this, though: values cannot go above 511, so there is still some rounding down of the colours going on, and when made more extreme (as is done in the tunnels in Proun), artefacts become visible because everything is made so much brighter. Those artefacts are rarely visible in Proun, but they are in this specific tunnel (still quite subtle, so this may be difficult to see on some monitors):

An extra benefit of doing HDRI, is that bright colours combine into new colours when blurred. This is kind of a weird side effect, but it looks really cool in the places where the spheres overlap in this image:

Which reminds me: I need to do something with explicitly coloured glow in a future game. Maybe have a bright brown object with a green glow or something like that. :)

Sunday, 5 September 2010

Failed/fixed leashing in Proun

Any level designer knows the word leashing: to lure the player into the right direction using things like light, colour and bright shiny power-ups. If you put the player in a large, open forest, you can still be almost certain where the player will go by making the entire forest slightly dark and lighting one patch really brightly. The player feels like he has the freedom to go where he wants, but he is on a psychological leash and the level designer gets to pull it. Come here, doggy, fetch the stick!

In track 2 in Proun, at the end of the lap there is a tunnel. There are obstacles in this tunnel and the player needs to avoid them, like this big yellow circle thingie:

Oddly, during playtests, I saw that about one in four players would rotate towards the obstacles, instead of avoiding them. Really strange, because in every other part of that track they immediately understood where they needed to go.

Then one of my testing victims (Marlies Barends, accidentally also the creator of this awesome animation) explained to me what was going wrong: the obstacle that you need to avoid has a bright colour, while the tunnel is a dull grey. Also known as: bad leashing!

The solution is simple: I put the light behind the obstacle instead of in front of it. Now the obstacle is in shadow and the tunnel behind it is brightly lit:

I haven't tested this on real dogs yet, but I expect them to know where to fetch the stick now! :)