softgym/PyFlex/demo/scenes/flag.h

class FlagCloth: public Scene
{
public:

	FlagCloth(const char* name) : Scene(name) {}

	void Initialize()
	{
		int dimx = 64;
		int dimz = 32;
		float radius = 0.05f;

		float stretchStiffness = 0.9f;
		float bendStiffness = 1.0f;
		float shearStiffness = 0.9f;
		int phase = NvFlexMakePhase(0, eNvFlexPhaseSelfCollide);
	
		CreateSpringGrid(Vec3(0.0f, 0.0f, -3.0f), dimx, dimz, 1, radius, phase, stretchStiffness, bendStiffness, shearStiffness, 0.0f, 1.0f);

		const int c1 = 0;
		const int c2 = dimx*(dimz-1);

		g_buffers->positions[c1].w = 0.0f;
		g_buffers->positions[c2].w = 0.0f;

		// add tethers
		for (int i=0; i < int(g_buffers->positions.size()); ++i)
		{
			// hack to rotate cloth
			swap(g_buffers->positions[i].y, g_buffers->positions[i].z);
			g_buffers->positions[i].y *= -1.0f;

			g_buffers->velocities[i] = RandomUnitVector()*0.1f;

			float minSqrDist = FLT_MAX;

			if (i != c1 && i != c2)
			{
				float stiffness = -0.8f;
				float give = 0.1f;

				float sqrDist = LengthSq(Vec3(g_buffers->positions[c1])-Vec3(g_buffers->positions[c2]));

				if (sqrDist < minSqrDist)
				{
					CreateSpring(c1, i, stiffness, give);
					CreateSpring(c2, i, stiffness, give);

					minSqrDist = sqrDist;
				}
			}
		}
		
		g_params.radius = radius*1.0f;
		g_params.dynamicFriction = 0.25f;
		g_params.dissipation = 0.0f;
		g_params.numIterations = 4;
		g_params.drag = 0.06f;
		g_params.relaxationFactor = 1.0f;

		g_numSubsteps = 2;

		// draw options
		g_drawPoints = false;
		g_drawSprings = false;
		g_windFrequency *= 2.0f;
		g_windStrength = 10.0f;

	}

	void Update()
	{
		const Vec3 kWindDir = Vec3(3.0f, 15.0f, 0.0f);
		const float kNoise = fabsf(Perlin1D(g_windTime*0.05f, 2, 0.25f));
		Vec3 wind = g_windStrength*kWindDir*Vec3(kNoise, kNoise*0.1f, -kNoise*0.1f);
				
		g_params.wind[0] = wind.x;
		g_params.wind[1] = wind.y;
		g_params.wind[2] = wind.z;	
	}
};