Explosion in VEX

[Ostap]

Hi:

If the wall is already broken into pieces (eg by the method of Voronoi), possibly do without DOPs, POPs SOLVER (do not need collision) to animate the explosion on pure mathematics for maximum speed and flexability ?

In this case, was meant: something impact on the wall and from this place fly away parts.

///

Error in name topic, was meant "Explosion without simulations"

Edited December 23, 2010 by Ostap

[pclaes]

It is possible, but it will require a bit of work to implement it. Sorry I can't share a scene file on this at the moment.

http://en.wikipedia.org/wiki/Trajectory_of_a_projectile

**EDIT

You would need to use a sopsolver (but only for the points that you will be instancing/copying/delayed loading your pieces onto)-> you need to iterate over time, so you can't really get around that.

Alright, you don't really need a sopsolver, you could use simply update the point along the arc defined by the equation by using $FF or any parameter/slider you want to link to it. I find sopsolvers handy as they allow me to store a history and calculate/trigger all kinds of other secondary usefull information + once it is cached you can scrub.

In terms of visualisation you could previs by building the lines/arcs first and then use a carve sop to extract points from those arcs. This is of course heavier and less accurate than using the equation to get the point - but you see what you are doing.

**END EDIT

This will help you get more speed: declare all your attributes on your initial geometry, do not create any new attributes as you go as this slows the multithreading of vex. When points become inactive, delete them from the simulation so they are not going to be calculated - this progressively speeds up your sim.

In regards to your attributes, make sure you update your up vector and N over time otherwise you will have issues when you need to instance your objects onto it. You can sort of give it a fake orientation linked to the change of rate of v, but that doesn't always work.

You can previs the paths of the pieces as they are just lines mapped to the equations of the trajectories. In terms of coordinate system all the wiki stuff is "2D", I would recommend sticking with that and add the 3rd coordinate by converting from x,y,z to polar coordinates. That way you are left with: angle of elevation (this will define your arc) and angle of rotation (generally around the y-axis, this will orient the initial v to face the target).

This will help you map those curves:

http://en.wikipedia.org/wiki/Range_of_a_projectile

In terms of control it is up to you if you rather set the initial velocity and/or angle of elevation, or if you rather use a target point that the piece is supposed to hit and calculate the other attributes from that target point.

This hopefully gives you a starting point.

Edited December 23, 2010 by pclaes

[Macha]

If you look at the last file I posted here:

Perhaps that gives you a slightly different pop-way to solve the problem.

[Ostap]

thanks Peter Claes, but should be simpler ways.

thanks "Macha", but you used POPs.

Edited December 24, 2010 by Ostap

[pclaes]

There used to be this tutorial as well:

http://www.vfxtalk.com/forum/two-hot-new-free-houdini-video-tutorials-t5077.html

But I can't find it, perhaps someone else knows if it's still around. That used a simple transform or a point sop to move the pieces around.

That won't give you very reallistic motion, but if it is just for impact and nothing much beyond that, even an animated displacement on a grid could do the job. Mixed with a blendshape of the target positions, that will give you arcing motion as well - completely non-physically correct, but it might work for your needs.

Have a look at the scene file for an easy mockup of the technique - It's fast, but needs tweaking to get it to look more real (that's where the phyics come in).

fake_explosion_01.hip

[Ostap]

Yes

pureMathematicExplode.hip

Edited December 23, 2010 by Ostap

[Ostap]

Yes, very similar to what I meant, but it seems I found a better way.

[pclaes]

Very clean! Nice!