SimonTheGuy Posted August 23, 2011 Share Posted August 23, 2011 Hey everyone, long time lurker, first time poster. I'm relatively new to Houdini, so I haven't felt confident in offering advice, but hopefully you all can offer me some. I'm working on a visual effect that deals with motion blur on the outline of objects within the scene. I have a camera/VOPSOP setup to affect point velocity along the edge of an object using dot product so that only the outer edge is affected. The purpose is to blend the outlines of the objects with the background. Below is an image of what I have so far which shows the effect but with various strange velocity anomalies. Right now in my VOPSOP I can only affect the point velocity direction through AA-Noise. It gives the blur that I want, but I'd like to be able to be able to have it be directed along the edge of the object rather than jutting out. That way it will be less drastic a change in velocity direction when there is motion. It was suggested to me that I use the Comb node, since the point velocity can be governed by the normal. So if I comb the normals like one would comb fur, the velocity would follow the normal direction and give me what I want. However, changing the normals has lead pretty wacky results. This may be a very "n00b" question, but is there a way I can comb the normals to affect point velocity, yet maintain the original normals for everything else? If not, is there another way? As it stands it changes the displacement I have on the object and makes it very blobby.Thanks for your time and I look forward to any response you might have. Quote Link to comment Share on other sites More sharing options...
Macha Posted August 23, 2011 Share Posted August 23, 2011 You can comb any vector, it doesnt have to be the normal. You could also comb normals, then with an attribute sop change the name from N to v an use a copy attribute sop to get the original normals back (or recalculate them) Quote Link to comment Share on other sites More sharing options...
Macha Posted August 23, 2011 Share Posted August 23, 2011 (edited) Oh, and a more procedural way 'may' be to use an edgeforce, rotate them around the normal so that they form a 0 dot with the eye direction. If you want them to point in the same direction perhaps you cross them with N, and again, add into a matrix get their determinant and flip them if they have differing signs (they idea is to create a matrix of bases and calculate the jacobian). Actually, maybe polyframe could help there. This is just an idea, I haven't tested it. Edited August 23, 2011 by Macha Quote Link to comment Share on other sites More sharing options...
anim Posted August 23, 2011 Share Posted August 23, 2011 here is one VOP SOP method of creating v pointing along edge from camera view, not sure if that's what you want edge_velocity.hip 1 Quote Link to comment Share on other sites More sharing options...
SimonTheGuy Posted August 23, 2011 Author Share Posted August 23, 2011 Wow, thanks a lot for the help guys. anim - I'll definitely play around with the VOP SOP and see how well it works compared to the non-procedural method. Macha - I had been looking at that Override Normal checkbox and thinking it had some sort of use, and sure enough changing it to v allows me to manually comb the velocity direction. I'll compare what it looks like with the two methods and post some results in a bit. Either way, I'm sure one of those two ways will get the job done. Thanks again. Quote Link to comment Share on other sites More sharing options...
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