Painting with motion tracking? 'Grow hair' along track, dynamic paint, bevel curve.

Dear community,
so after a few years I’m back to blender for a media project I’m launching and, just to say, how the program has grown is AWESOME! :smiley:

I got one problem I can’t find a solution. The idea is that I’m in front of the camera, and paint into the air with a nice, clear, very professionally looking line :wink:

So, for example, in this test I’m in front of the cam and the saccharine in my hand is tracked.

Now I’d like the line to be a nice, rounded line.

One way to do it is to make a UV sphere follow the track, add a plane as a canvas and use dynamic paint. The disadvantage of this is that to make it very precise, the paintmap needs to have a very high resolution and many substeps. Nevertheless, if I don’t find another way, that’ll be how I do it.

Another maybe something with particle systems. In the image a 1-vertex object emits particles. One obvious way to get to a line is to simply increase particles until they connect :wink: But is there a less messy way to ‘connect’ these particles? Like make a hair grow along the animated path of an object?

My preferred option would be if there were an option to convert the motion tracking into a curve! Because then I could simply animate the bevel of the curve – which since 2.71 with CND’s Bevel Factor Mapping isn’t a problem any more :slight_smile: That would be by far the most efficient and neat solution I think. So is there a way to convert all positions of a motion tracking track into a curve?

Thanks very much for your attention.

Regards, Marc

a quick thing I just tried…

  1. track your object from video
  2. solve > geometry > link empty to track
  3. track object panel > calculate Motion Path
  4. run this little script to get a curve from the motionpath
  5. bevel the curve -Map Taper option can give nice shapes-
  6. animate bevel End factor, set interpolation to linear

seems to work but may be smarter ways to do it -or a script could take care of all steps-

@liero: i’m very sorry i never saw this message! :slight_smile: thanks a lot! i’ll use that in the future!