# Ambient occlusion textures - As part of the lighting setup, we run a radiosity simulation over the entire city which works by firing 16 million million photons (that is 16x (10^12) photons) into the geometry). Their effect is then measured at approximately 32,000 million points. We save out the results as textures and apply these to the environment. We wrote our own custom tools to achieve this which, as well as being of a much higher quality than those from our 3-D package, they also meant a 100X reduction in computation time!
# Surface textures - To get all the detail, blending, and radiosity effects in the environment requires no less that six texture maps - four for colour, and two for lighting. Also, the blends between all those maps vary across the surface to provide more variation which is a gigantic amount of data to set up on each surface. Again our need for full precision control meant we produced custom tools for the job.
# Outlines on everything – This is a fundamental part of the game style and we wrote three versions before finding a method that was antialiased and had a reasonable render cost. We're achieving the effect by leveraging the Xenon's MSAA hardware in a new and unusual way.
# Fake window interiors – The technology we're using for windows is the next generation beyond parallax mapping. For every pixel of every window, the shader simulates raytracing through the blinds, through the interior window box, and finally into the room until it hits the floor or ceiling. And after that, the full lighting equation is run.
# Procedural Sky – The whole sky including the clouds is completely procedurally generated. The sky is blue and sunsets are red because of Rayleigh scattering - the effect of blue wavelengths of light being more likely to bounce off air molecules than red ones are. We run an approximation to the double integral needed to compute Rayleigh scattering - and we do it for every pixel of sky, for every frame. In addition, the shape of the clouds is procedurally generated by the GPU. Like the sky, all the lighting on the clouds is run by the GPU for every single pixel of sky, every single frame.
Our decision to go with our impressive deferred lighting technique to allow thousands of lights visible across the world at any given time was the making of the night time vista and this was the icing on the cake that we think helped people to truly appreciate the decisions we’d made. This can only be hinted at in a screenshot but to see the entire city with thousands of streetlights to the distance, thousands of characters walking around and hundreds of moving vehicles with headlights really is an impressive sight
Well designed lighting was going to be the key to the success of the Crackdown look but after some months experimenting with the basic system, it was evident that it wasn’t going to cut it. The exaggerated palette was very sensitive to even the slightest lighting changes and on occasion this unfortunately meant we submitted screens from builds with some pretty garish colouring (our orange and purple extravaganza at X05 was not one of our finest moments )
