Monday, February 04, 2008

Impostering

I've now finally implemented the Paged Geometry engine into Ember. This is an component which allows for much more nicer looking foliage through a variety of different techniques. While we've had grass through the use of batched geometry for a while, the implementation wasn't really optimal and it didn't contain the more advanced features needed. The main thing lacking has always been a proper implementation of imposters, which are 2d billboards used in the distance. Instead of burdening the GPU with full geometry for far away trees, which in the end will end up just taking up a few pixels on screen, we render the tree once to a 2d sprite and reuse that. The end result is an enormous speed up for forests scenes, where there can be thousands of trees on the screen at any one time.
All of this is provided by the Paged Geometry engine, which is why I'm very excited to finally have it in place. So far I've partially converted the grass system to use the new engine. It's currently lacking some of the filtering features, which makes the grass appear on paths and other areas where there should be no grass. It's also just randomly dispersed, which makes it look a little bit unnatural. It would preferably be dispersed in a more cluster like fashion, to better simulate the way grass grows in the real world. All of this is currently being addressed however.
The trees now use billboards when viewed from afar. I've extended the Model format to take an additional "rendering scheme" subsection. This allows one to specify different rendering schemes for different models. Thus we can tell Ember to use the rendering scheme "forest" for our trees, which will set up everything and make them switch to imposters at far away distances, while keeping the regular entity rendering at close distance. The Paged Geometry engine allows us to use batched geometry up close, which means that the different entities are "baked" into one large mesh. However, due to the dynamic nature of Ember and the Worldforge world that's not feasible. Thus we need to render the entities normally up close. The current solution is to do that using the regular rendering system and then set max render distance to the same distance as that when imposters take over. But since the imposters work in groups the distance where a certain entity begins to be rendered by imposters isn't exact. This means there are instances where this leads to either both the imposter and the entity being rendered at the same time (not a big problem) or that none gets rendered (a bigger problem). I therefore need to extend the Page Geometry engine with some Ember specific classes which will allow it to smoothly transition between normal entity rendering and imposter rendering.
I've already made some refactoring changes to the Page Geometry, which I intend to try to push back into the main development branch.
I've put up some more screen shots of the imposters and grass over at amber.

On a different note, there have recently been some issue with the Worldforge infrastructure. I've been trying to contact Balinor about the media svn for some time, but have never gotten any response. Last week however the svn server completely broke down: when trying to update I get a message about an internal error. A quick google shows that it stems from the server running out of disc space. This is bad, since not only can no one commit to the repository, no one can even update their local copy against it. I therefore sent some emails to the mailing lists, only to find that they also have been broken. Apparently there was a purge of all the old inactive lists last week, something sorely needed. Instead of having 15+ different lists, we now only have 4, which hopefully will mean that messages won't be lost. Unfortunately this changes seems to have broken the lists, since none of my mails got to the lists. I've been trying to contact the people responsible this weekend to no avail, but hopefully it will be fixed soon.
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