Writing ink on paper

[LFX]

Hello all!

A little learning by doing for me. Maybe someone have a better start point for this.

Desired effect:

Animation of writing ink with dry off on paper. In a macro detail.

Current state:

I'm placing a line of particles and copy metaballs on them. Through a channel, which shifting with the animation, the metaballs at the farther get scaled down in Y.

Current Problem:

The result becomes also 'thinner' in the end.

Kind Regards

Edited March 1, 2010 by LFX

[mightcouldb1]

You will get better results if you use a shader for this in my opinion. You can create a wetmap and add some displacement that changes over time. Watch Peter Quint's wetmap tutorial on vimeo or search wetmap on the forums.

Jason

[LFX]

Oh yes, you are right. That way I could just translate it down, instead of scaling. I had a plan with the metaballs regarding the fuzziness on the edges of lines on paper. But I guess there will be a better solution, too.

[Macha]

For the scaling you could add a ramp when you create the attribute and then have very good control of how the thickness evolves.

[LFX]

OK, thanks for the feedback. But the scaling isn't the problem anymore. I would have gone into micro detail with metaballs all the way. I let them fade out now and want to leave an ink line via shading. For this I want to create a bias-map synchronously with COPS.(I leave the wetmap approach for now, because of performance and more control over the line shape.) I translate a dot in an add-COP proportional to the transform of the particle emitter, and add it to the dot from one frame before and so on, till I get the line.

Current Problem:

Houdini doesn't like to load the image it's written one frame before, because the image is not there yet.

[LFX]

After scripting a COP-Network with an add-COP for every emitted particle, I have to admit that it's no performance gain. Beside that, it's working. Will go on now with the wetmap approach. But I don't need the particles for that. So let's see how to save these points and still get a nice drop line.

[LFX]

I've made all a little slick and clean and add a ramp as controller for the drop line. Now I'm into this painting thing. Directly changing the colors of the points gives a too rough representation. I'm a noob when it comes to VOPs, so I ask myself is there any way to color an area with UV coords, like with a bitmap. Because I have this nice particle line which would give positions for the pixels. But I guess there is a much straighter way...

[LFX]

As always, the cleanest result you get with boolean, is with no divisions on one object. This will give me a nice selection for shading, and could come in handy for fancy effects. You see, I came to a point, where I want to make an HDA, and to keep a wide range of possibilities.

There is one thing which makes me wonder. Why does the polygon representation of meta balls looses detail on every added meta ball?

Edited March 22, 2010 by LFX

[old school]

There is one thing which makes me wonder. Why does the polygon representation of meta balls looses detail on every added meta ball?

What you see in the viewport is the polygon representation of the metaballs. You only have so much level of detail.

If you want to see the metaballs converted and renderd more accurately in the viewport, open up the Display Preferences and in the Optimize tab increase the Level of Detail or LOD. This will slow down the viewport update speed.

Sometimes it is better to convert the metaballs in to polys yourself via the Convert SOP or Convert Meta SOP.

[LFX]

OK, after a long period of R&D I can say that the cookie-SOP is not capable of creating a line, as soon as it gets more complex than a ball. I have another technique in mind, but no time anymore. So I will leave the hip-file here for everyone whose interested, in how far you can get with the cookie-SOP.

drawing_tool.hipnc

Edited May 11, 2010 by LFX