So, one of the things the project I’m ripping off did to add variety was to make some buildings slightly yellow, and some buildings slightly blue. Yesterday’s update was still looking a bit homogenous, so in the spirit of ripping off everything, I decided to implement the same thing. And it now look like this:

Now, this took a bit of doing. Because we batch up all our rendering, we try to change as little state during rendering as we possibly can – so, for example, we could have added an extra parameter to the shader to add a tint to everything rendered. However, this parameter would only have been changable between batches, which means we’d have to batch like-coloured buildings together – which would be entirely possible, at the moment, but later on I plan to exploit spatial proximity between buildings to produce batches for culling, and having to produce three batches per region would add complexity and potentially reduce performance.

So, the other place we can pass in static data? In the vertices. Each vertex could have a colour attached to it – this way, so far as our batching is concerned, all buildings are still equal. The downside is, there’s no space in our current vertex format (VertexPositionNormalTexture) for this information. One possibility is to turn off lighting (the city is at night-time, remember?) but I’ve got other plans for that, too, so the best option seemed to be to roll my own vertex format – VertexPositionNormalTextureMod – which simply adds another Vector3 to VertexPositionNormalTexture. Then it’s just a case of changing all my buffers over to use this format, add the relevant extra data and make the appropriate changes to the shaders to do the actual tinting.

Pleasingly, this didn’t seem to affect framerates at all (at least, not on the number of buildings I’m working with at the moment), and the effect is quite lovely – it adds some much needed variety to the scene.

The latest revision is 21 in the repository – there wasn’t a trunk revision attached to update 6, but you can check out revision 7.1.13 if you want to have a look at that.

Tags: batching, c#, Cityscape, custom vertex format, prettification, programming, XNA

This entry was posted on Monday, May 25th, 2009 at 2:55 pm and is filed under Cityscape. You can follow any responses to this entry through the RSS 2.0 feed. Both comments and pings are currently closed.