Posts Tagged ‘fog’

Cityscape – Update 8

Wednesday, May 27th, 2009

Unfortunately, today’s minimised screenshot doesn’t look so hot (I guess it’s something to do with Flickr’s contrast enhancing algorithm), so if you want to get an idea of the latest developments, you should probably click through to the original image on Flickr to see it properly.

The big news this time is that I’ve added lighting attentuation and fogging – cities are big, nasty polluted things, and it’s rare that you can see more than a couple of blocks anyway – plus, it means that when I add in distance culling in a while, I we hopefully shouldn’t see things pop in and out too obviously 🙂

Lighting attenuation is just the light falloff as things get further away from the light – I’m not 100% convinced it’s worthwhile at the moment, though. Fogging is very similar: a gradual blend towards the fogging colour (in this case, it’s the same colour as the sky) as distance from the viewer increases.

Both of them are very simple to implement in our shaders – a couple of parameters to control falloff and fog colour, and a little bit of extra code to calculate the light falloff/fogging amount – basically, 1/(distance * k), where k is a more-or-less arbitrary fudge factor. The actual fog blending has to be done in the pixel shader, as we need to interpolate between the final resultant colour, lighting, texture and all, and the fog colour. This unfortunately utterly kills framerate on Intel integrated graphics chipsets; their poor little pixel pipelines just can’t take it. There’s actually a better way to do fogging than this on shader model 1.1 chipsets – the shader model actually supports fogging parameters – so I might implement a version for Intel chipsets that uses this mechanism and see if it improves matters.

I’ve also changed the building generation code: I’ve factored out an IBuilding interface and a BaseBuilding that can be simply inherited from to create different building types – I’ve renamed my existing building class UglyModernBuilding, and added a SimpleBuilding (a straightforward single block building). I’ve also factored out the actual geometry generation methods into another class, BuildingBuilder. I’m beginning to think Building.cs is getting a bit unweildy now, so there might be more changes/tidyups to come.

So, you’ll notice the polys/sec is well down: about 8 million polys per second now. I’m not entirely sure what’s causing this – turning any one of my individual effects off doesn’t seem to recover the framerate so it’s probably something more subtle. I’m not that worried about this right now, as 8 million polys per second is still pretty respectable, but I’ve got plans for more complex buildings pretty soon, which is going to eat into that budget pretty quickly, and necessitate either finding some more polys/sec, or implementing some sort of distance culling or LOD twiddling fairly soon.

Anyway, the latest bzr revision is 23; have a look if you like.