[EDIT]
This thread has been split due to it having an inappropriate title for the change of direction in the discussion. The original section is here:
http://forums.planetside.co.uk/index.php?topic=2202.0It was initially started by AndyWelder as a bug thread due to extreme displacement spikes being cut off at render time. Andy wanted to render extreme spikes to create grass like surfaces. Volker then posted about a problem he had with sharp spikes not rendering where he wanted to create Mojoesque type spires. He included this as an example and the discussion progressed from there:
We eventually recreated (or rather emulated because Mojoworld has sparse convolution function that can create spikes) the same technique as used in Mojoworld and a final tgd file was created. Some other ideas are in here as well and may be explored further. Thanks to Volker for solving one issue that enabled us to recreate this technique.
[/EDIT]
Off track a bit from Andy's post but it relates due to spike rendering problems.
That's great Volker. I know you have seen my render called Twisters that looks quite Mojo. All I had in that was a terrain from one fractal that had some spikes here and there and my displacements increased scale and amplitude with altitude. There is a thread somewhere on this forum about the scale increase with altitude, but I changed the graph a little - it had some nodes that were not crucial. It's not right yet though. Displacement amplitude works fine because you just manipulate the altitude output to get a suitable result back for the required amplitude but there are some problems with the scale driving by altitude in the way the different dimensions stretch that I have to solve yet.
This is kind of related to your results here but is still totally unrelated to my technique in Twisters. In this example below I used tall fake stones and sent the graph in the screenshot to the stones shader input. Ideally what we really want is a sparse convolution basis because that will get really smooth spikes, not so broken when displaced a lot but there are ways to smooth out the voronoi edges I think, at least I have definitely done that in the past (somehow) but now I can't remember exactly how I did it. Spikes are done with sparse convolution in Mojo. We need spikes that do not end it sharp points because that often ruins the displacement at the point - you can see this in my image and rendering problems occur. The compute normal is there because I displaced by lateral normalized in the displacement shader. Fake stones are convenient at this stage ot experiment being already set up to have a different shader. It's still X,Y,Z (X and Z are multiplied as you can see in the graph and thus stretched out) related though which is not entirely what I want but like I say there are some problems with using altitude to change the scale anyway - which is really what I wanted rather than just stretching in X,Y or Z. I will get my head around that one way or another. Once I get it to something better than has been previously discussed I will post about it.
This is slightly unrelated to Andy's initial post though because he was talking about actually rendering the spikes. I like that idea a lot but for our rock spires we want to actually avoid such sharp spikes so that it all renders and with less distorted displacements at the point.
