# HG changeset patch
# User John Tsiombikas <nuclear@member.fsf.org>
# Date 1452536653 -7200
# Node ID dc15b741486c40a6179dd4710464bb8facc4427a
# Parent  ef0c22554406d8b8fadd1ba5305aaf782cdf2486
exploding cloth

diff -r ef0c22554406 -r dc15b741486c src/cloth.cc
--- a/src/cloth.cc	Mon Jan 11 16:51:16 2016 +0200
+++ b/src/cloth.cc	Mon Jan 11 20:24:13 2016 +0200
@@ -9,6 +9,7 @@
 	mass = 1.0;
 	elast = 0.8;
 	spring_k = 1.0;
+	damping = 0.01;
 	grav = Vector3(0, -9, 0);
 }
 
@@ -31,7 +32,7 @@
 			masses[idx].pos.x = (float)j * dx - width / 2.0;
 			masses[idx].pos.y = 0;
 			masses[idx].pos.z = (float)i * dy - height / 2.0;
-			masses[idx].fixed = i == 0 && (j == 0 || j == x - 1);	// XXX debug hack
+			masses[idx].fixed = i == 0;	// XXX debug hack
 			++idx;
 		}
 	}
@@ -43,10 +44,10 @@
 			conn[idx][idx] = -1;
 
 			// connect node to its neighbors
-			for(int ni=0; ni<5; ni++) {
-				for(int nj=0; nj<5; nj++) {
-					int nx = j + nj - 2;
-					int ny = i + ni - 2;
+			for(int ni=0; ni<3; ni++) {
+				for(int nj=0; nj<3; nj++) {
+					int nx = j + nj - 1;
+					int ny = i + ni - 1;
 
 					if(!nx && !ny) continue;
 					if(nx < 0 || nx >= x || ny < 0 || ny >= y) continue;
@@ -63,6 +64,36 @@
 	}
 }
 
+void Cloth::set_mass(float m)
+{
+	mass = m;
+}
+
+void Cloth::set_elasticity(float e)
+{
+	elast = e;
+}
+
+void Cloth::set_spring_constant(float k)
+{
+	spring_k = k;
+}
+
+void Cloth::set_damping(float d)
+{
+	damping = d;
+}
+
+void Cloth::set_gravity(const Vector3 &g)
+{
+	grav = g;
+}
+
+void Cloth::set_force(const Vector3 &f)
+{
+	forces = f;
+}
+
 void Cloth::transform(const Matrix4x4 &xform)
 {
 	for(size_t i=0; i<masses.size(); i++) {
@@ -79,25 +110,35 @@
 {
 	int num_masses = (int)masses.size();
 
+	Vector3 *newp = new Vector3[num_masses];
+
 	for(int i=0; i<num_masses; i++) {
-		if(masses[i].fixed) continue;
-
-		Vector3 newpos = masses[i].pos + masses[i].vel * dt;
+		if(masses[i].fixed) {
+			newp[i] = masses[i].pos;
+			continue;
+		}
 
 		Vector3 force = grav + forces;
 
 		for(int j=0; j<num_masses; j++) {
-			if(conn[i][j] <= 0.0) continue;	// skip unconnected
+			if(i == j || conn[i][j] <= 0.0) {
+				continue;	// skip unconnected
+			}
 
 			Vector3 dir = masses[j].pos - masses[i].pos;
 			float dist = length(dir);
+			float disp = dist - conn[i][j];
+			if(fabs(disp) < 1e-5) disp = 0.0f;
 
 			// apply an impulse based on the displacement from the original state
-			force += dir * (dist - conn[i][j]) * spring_k;
+			force += dir * ((disp * spring_k) / dist * 0.5);
 		}
 
 		// update the velocity by integrating the accumulation of all forces
-		masses[i].vel += force * dt;
+		Vector3 accel = force / mass;
+		masses[i].vel = masses[i].vel * (1.0 - damping) + accel * dt;
+
+		Vector3 newpos = masses[i].pos + masses[i].vel * dt;
 
 		Ray ray;
 		ray.origin = masses[i].pos;
@@ -108,8 +149,15 @@
 			newpos = pt.pos;
 			masses[i].vel = reflect(masses[i].vel, pt.normal) * elast;	// TODO collider elasticity
 		}
-		masses[i].pos = newpos;
+		//masses[i].pos = newpos;
+		newp[i] = newpos;
 	}
+
+	for(int i=0; i<num_masses; i++) {
+		masses[i].pos = newp[i];
+	}
+
+	delete [] newp;
 }
 
 bool Cloth::find_collision(const Ray &ray, HitPoint *hit) const
diff -r ef0c22554406 -r dc15b741486c src/cloth.h
--- a/src/cloth.h	Mon Jan 11 16:51:16 2016 +0200
+++ b/src/cloth.h	Mon Jan 11 20:24:13 2016 +0200
@@ -16,6 +16,7 @@
 private:
 	float mass, elast;	// global mass attributes
 	float spring_k;		// spring constant for all springs
+	float damping;
 	Vector3 grav, forces;
 
 	std::vector<ClothMass> masses;
@@ -30,6 +31,13 @@
 
 	void create_rect(int x, int y, float width, float height);
 
+	void set_mass(float m);
+	void set_elasticity(float e);
+	void set_spring_constant(float k);
+	void set_damping(float d);
+	void set_gravity(const Vector3 &g);
+	void set_force(const Vector3 &f);
+
 	void transform(const Matrix4x4 &xform);
 
 	void add_collider(Object *o);
diff -r ef0c22554406 -r dc15b741486c src/main.cc
--- a/src/main.cc	Mon Jan 11 16:51:16 2016 +0200
+++ b/src/main.cc	Mon Jan 11 20:24:13 2016 +0200
@@ -19,7 +19,7 @@
 void mouse(int bn, int st, int x, int y);
 void motion(int x, int y);
 
-float cam_theta, cam_phi, cam_dist = 8;
+float cam_theta, cam_phi = 25, cam_dist = 10;
 
 Cloth cloth;
 
@@ -55,13 +55,17 @@
 	//glEnable(GL_LIGHTING);
 	glEnable(GL_LIGHT0);
 
-	cloth.create_rect(32, 32, 10, 10);
+	cloth.create_rect(4, 4, 10, 10);
 
 	Matrix4x4 xform = Matrix4x4(1, 0, 0, 0,
 								0, 1, 0, 0,
 								0, 0, 1, 0,
-								0, 1, 0, 1);
+								0, 1, 1, 1);
 	cloth.transform(xform);
+	cloth.set_mass(0.1);
+	cloth.set_spring_constant(0.1);
+	cloth.set_gravity(Vector3(0, -0.1, 0));
+	cloth.set_damping(0.1);
 
 
 	return true;
@@ -73,6 +77,14 @@
 
 void display()
 {
+	static unsigned int prev_upd;
+	unsigned int msec = glutGet(GLUT_ELAPSED_TIME);
+
+	if(!prev_upd) prev_upd = msec;
+	float dt = (msec - prev_upd) / 1000.0f;
+
+	cloth.step(dt);
+
 	glClear(GL_COLOR_BUFFER_BIT | GL_DEPTH_BUFFER_BIT);
 
 	glMatrixMode(GL_MODELVIEW);