How we trashed buildings in SimCity 4

At it's heart, SimCity 4 was a giant, realtime compositing engine. The city was displayed isometrically, so we could render stuff to the screen, and not update it until something changed.
Since we didn't have to redraw everything 30 times per second, I could overlay many layers to build up the visual richness that I was after.

Here's one example that I mocked up while trying to figure out how we were going to represent building decay (an important game feedback that needed to read clearly).

Let's say that you start out with this brand new, squeaky clean building:


Each building could have it's own custom, automatically generated "crud" map (a combination of ambient occlusion and 3D noise rendered through the source geometry).
Just multiply it over the base building to make it dirty.


Each building could also have automatically generated window masks (normally used to make the windows glow at night). Just multiply those over the building and the windows start looking dark and dingy.


We could break the window masks into sections and apply them independently for a further stage of decay (we didn't wind up doing that, having to save memory as I recall)


As things go from bad to worse, we could mask a tiling boarded-up-window texture through one of the window channels.


Since the game was in an isometric perspective, we could pre-render "crater" decals and lay them over the building, making it look like parts of the facade had fallen off.



And lastly, for that 12 Monkey's, abandoned Philadelphia look, we could overlay an automatically generated snow mask.


In the end we didn't wind up doing all of these things, running short of memory and disk space for all of the masks I wanted (times 4 rotations and 5 zooms!) But this was what I was after, and (thanks to Paul Pedriana's graphics engine) we got pretty close.

O.