[Sidefx-houdini-list] tracking via cops/pic()

Alvin Yap alvinyapvfx at gmail.com
Thu Aug 20 18:58:10 EDT 2009

Hmmm... let's say you have a 1 red sphere moving on a black background.
Use the pic expression to pull in the color data from cops to sops
Time shift the geometry by -1F.
Merge the timeshifted geo with the current time's geo.
Instance geometry onto those red points.
Use a bounding box or some xmax-xmin expression to determine how large the
bounding box is for this frame and last frame.
Hence if the bounding box between the last and current frame is very small,
less movement. If the returned bounding box is huge, lots of movement.
Use that to drive particles?

Too lazy to boot up houdini now- whole day on it ;-)


On Thu, Aug 20, 2009 at 11:31 PM, jacob fisher <jacobfshr at gmail.com> wrote:

> Hopefully this will be a simple question I have and you all won't
> think less of me, but here goes.
> I have an image sequence I imported into COPs and I have it copied to
> a grid via a pic() command in the point node.
> What I'd like to do is have a reaction based off the movement of an
> object in the image sequence.
> As a sphere moves from right to left, I would like a particle
> simulation to occur.  However, I would like the particle simulation to
> be varied depending on how quickly the sphere is moving.  So if it's
> moving at 3 pixels/rows/columns/whatever a frame it will release more
> particles than if it moves at 1 pixel per frame.
> How would I go about tracking this?
> Thanks for any tips you can think of.
> -jake
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