UPDATE: The O2 Engine has come a long way after this post. It is now is directly tied into content pipelines with modelers like Blender and is capable of achieving far better lighting than what is presented here. This post talks about lighting in a fixed function pipeline which is pretty old technology. The Doofus game is released and can be found at www.doofuslongears.com.
Some preview of the lighting technology used in the game. This is not an in-depth explanation of it, but is just a preview so don’t expect technical details here. Maybe sometime later, (I will fill in the details) or you can just ask and I will be glad to explain it.
The lighting in Doofus works on several levels, ie passes. The passes are then composited to give a final image. This technology is not revolutionary and I certainly haven’t invented anything new, but I have used in a clever way so that it can run even on old h/w without much difficulty. It also gives the scene a nice cartoon effect.
First the scene is rendered normally with the basic lighting of OpenGL or DirectX. The O2 engine abstracts over both APIs and can use any one. The results of basic lighting can be seen in this image. (Click on the images to see a larger version of that image.)
This type of lighting is pretty basic. The scene seems pretty bland and devoid of any real excitement. This lighting shown here is the default vertex based lighting given by the rendering APIs.
The real excitement comes to the scene when shadows get added to the scene. In case of the O2 engine and the Doofus game I am using Stencil Shadows. 
Stencil shadows give hard crisp edges. That goes nicely with the cartoon theme of the game. In the next image you can see the shadows added to the scene. Along with shadows I have added a extra brightening pass i.e. Portions not in shadows are brightened up. That gives an illusion of soft sunlight (, the kinda sunlight you have very early in the morning).
Shadows add cohesion and drama to the scene. You can see a stark contrast between the two images, the one above without and the one on the right with shadow. The “drabness” of the scene is gone.
Things don’t end here. To have actual sunlit environments you have to have a super-bright component to the sunlight. Meaning, if you watch actual sunlight you will see that it is extremely bright with a halo like effect created at each shadow’s edge. For this, the engine does on more pass and applies a bloom filter to the scene to emulate sunlight.
The resulting scene looks actually sunlit, with the sunlight shining off bright surfaces. Watch the shadows boundaries closely, you will see what I mean. Now the scene looks correctly lit by sunlight.
Finally I want to show how the engine displays the sun. Observe the image on your right. You can see the sunlight bleeding through the edges of the roof just like an actual sun would when viewed across occluding geometry and notice the sun rays filtering through. The engine uses a similar variation of the multi render pass system explained earlier to achieve this effect. Just comes off looking great!
All images are actual game images captured while running the game in real-time. You can find more images of the game in the gallery section on my site.
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