Grass in toxiclibs - Verlet Physics?

bjzaba

Grass in toxiclibs - Verlet Physics?

in Contributed Library Questions • 2 years ago

I'd like to make some grass that responds to wind and gravity:

I've been struggling with this for over week now (yes, I'm an artist - ie. not a very good programmer). Today my friend suggested I look into Verlet Physics, and to my delight I found that it was sitting right there under my nose in toxiclibs. The bundled examples are quite helpful, especially the one called 'ThreadDemo'.

I managed to get some gravity and wind working in ThreadDemo adding some physics behaviours:

physics.addBehavior(new GravityBehavior(new Vec2D(0, 0.5)));
physics.addBehavior(new ConstantForceBehavior(new Vec2D(0.2, 0)));

The problems I'm facing are:

preserving the length between the particles (I don't want the blades of grass to look like elastic bands).
giving the particle string some rotational stiffness (so that it can counteract the net force of the wind and gravity).

Replies(4)

bjzaba

Re: Grass in toxiclibs - Verlet Physics?

2 years ago

Ok, new problem (on top of the others):

When I try to use the same physics behaviours in Eclipse instead of the processing IDE, I get this:

bjzaba

Re: Re: Grass in toxiclibs - Verlet Physics?

2 years ago

Ok, well I worked out a hacky solution to this:

// initialise forces
Vec2D gravity = new Vec2D (0, 1);
Vec2D wind = new Vec2D (0.5f, 0);
// add this to the draw function
for (VerletParticle2D particle : physics.particles) {
particle.addForce(gravity);
particle.addForce(wind);
}

Shame the inbuilt behaviours don't work though.

I'm actually thinking this may lead to a solution to the grass problem though. Now that I've worked out that I can alter the properties of each individual particle, perhaps I could implement something similar to the rotational stiffness mentioned in the wikipedia article I posted previously:

A body may also have a rotational stiffness, k, given by

$k=\frac {M} {\theta}$

where

M is the applied moment

θ is the rotation

In the SI system, rotational stiffness is typically measured in newton-metres per radian .

In the SAE system, rotational stiffness is typically measured in inch- pounds per degree .

Further measures of stiffness are derived on a similar basis, including:

shear stiffness - ratio of applied shear force to shear deformation

torsional stiffness - ratio of applied torsion moment to angle of twist

Any thoughts would be most appreciated!

toxmeister

Re: Re: Grass in toxiclibs - Verlet Physics?

2 years ago

Hey, my guess is that you have accidentally imported the 3d verlet physics packages and not the 2d versions. you need to use these two import statements for 2d:

import toxi.physics2d.*;

import toxi.physics2d.behaviors.*;

GravityBehavior & ConstantForceBehavior (as 95% of the whole physics API) are available for both 2d & 3d, but each can only be used with their related version of VerletPhysics or VerletPhysics2D...

Hth! K.

http://postspectacular.com | http://toxiclibs.org

bjzaba

Re: Grass in toxiclibs - Verlet Physics?

2 years ago

Wow! That worked, thanks for that! :)

Any quickish suggestions on the grass front?

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