From 6a6b355866e9c227415ed028966362d3760353de Mon Sep 17 00:00:00 2001
From: Eleni Maria Stea <estea@igalia.com>
Date: Sun, 6 Jan 2019 09:34:48 +0200
Subject: [PATCH] added forces + damping, k factors

---
 src/hair.cc |   52 +++++++++++++++++++++++++++++++++++++++++-----------
 src/hair.h  |    1 +
 src/main.cc |   15 +++++++++++----
 3 files changed, 53 insertions(+), 15 deletions(-)

diff --git a/src/hair.cc b/src/hair.cc
index 2431f50..0fc026d 100644
--- a/src/hair.cc
+++ b/src/hair.cc
@@ -8,6 +8,11 @@
 #include "kdtree.h"
 #include "hair.h"
 
+/* spring constant */
+
+#define K_ANC 4.0
+#define DAMPING 1.5
+
 struct Triangle {
 	Vec3 v[3];
 	Vec3 n[3];
@@ -122,7 +127,7 @@ bool Hair::init(const Mesh *m, int max_num_spawns, float thresh)
 
 	for(size_t i=0; i<hair.size(); i++) {
 		hair[i].pos = hair[i].spawn_pt + hair[i].spawn_dir * hair_length;
-		
+
 		/* orthonormal basis */
 		Vec3 vk = hair[i].spawn_dir;
 		Vec3 vi = Vec3(1, 0, 0);
@@ -137,7 +142,7 @@ bool Hair::init(const Mesh *m, int max_num_spawns, float thresh)
 
 		for(int j=0; j<3; j++) {
 			float angle = (float)j / 3.0 * 2 * M_PI;
-			/* dir of each anchor relative to hair end */
+			/* dir of each anchor relative to hair root */
 			Vec3 dir = Vec3(cos(angle), sin(angle), 0);
 			dir = basis * dir;
 			hair[i].anchor_dirs[j] = hair[i].pos + dir - hair[i].spawn_pt;
@@ -146,32 +151,40 @@ bool Hair::init(const Mesh *m, int max_num_spawns, float thresh)
 	return true;
 }
 
+static Vec3 dbg_force;
 void Hair::draw() const
 {
 	glPushAttrib(GL_ENABLE_BIT);
 //	glDisable(GL_DEPTH_TEST);
 	glDisable(GL_LIGHTING);
 	glPointSize(5);
-	glLineWidth(2);
+	glLineWidth(3);
 
 	glBegin(GL_LINES);
 	for(size_t i=0; i<hair.size(); i++) {
 		glColor3f(1, 0, 1);
-		glVertex3f(hair[i].pos.x, hair[i].pos.y, hair[i].pos.z);
-		Vec3 p = hair[i].spawn_pt;
+		Vec3 p = xform * hair[i].spawn_pt;
 		glVertex3f(p.x, p.y, p.z);
+		Vec3 dir = normalize(hair[i].pos - p) * hair_length;
+		Vec3 end = p + dir;
+		glVertex3f(end.x, end.y, end.z);
+/*
+		glColor3f(1, 1, 0);
+		glVertex3f(hair[i].pos.x, hair[i].pos.y, hair[i].pos.z);
+		Vec3 end = hair[i].pos + dbg_force * 2.0;
+		glVertex3f(end.x, end.y, end.z);
+		*/
 	}
 	glEnd();
 
+	/*
 	glBegin(GL_POINTS);
 	glColor3f(0.5, 1.0, 0.5);
-	for(size_t i=0; i<hair.size(); i++) {
-		for(int j=0; j<3; j++) {
-			Vec3 p = hair[i].spawn_pt + hair[i].anchor_dirs[j];
-			glVertex3f(p.x, p.y, p.z);
-		}
+	for(size_t i = 0; i < hair.size(); i++) {
+		Vec3 p = xform * (hair[i].spawn_pt + hair[i].spawn_dir * hair_length);
+		glVertex3f(p.x, p.y, p.z);
 	}
-	glEnd();
+	glEnd();*/
 
 	glPopAttrib();
 }
@@ -180,3 +193,20 @@ void Hair::set_transform(Mat4 &xform)
 {
 	this->xform = xform;
 }
+
+void Hair::update(float dt)
+{
+	for(size_t i = 0; i < hair.size(); i++) {
+		/* in local space */
+		Vec3 hair_end = hair[i].spawn_pt + hair[i].spawn_dir * hair_length;
+		Vec3 anchor = xform * hair_end;
+
+		Vec3 force = (anchor - hair[i].pos) * K_ANC;
+
+		Vec3 accel = force; /* mass 1 */
+		hair[i].velocity += ((-hair[i].velocity * DAMPING) + accel) * dt;
+		hair[i].pos += hair[i].velocity * dt;
+
+		dbg_force = force;
+	}
+}
diff --git a/src/hair.h b/src/hair.h
index 23aff83..6cbf14e 100644
--- a/src/hair.h
+++ b/src/hair.h
@@ -28,6 +28,7 @@ public:
 	void draw() const;
 
 	void set_transform(Mat4 &xform);
+	void update(float dt);
 };
 
 #endif //PARTICLES_H_
diff --git a/src/main.cc b/src/main.cc
index 307f647..54959a8 100644
--- a/src/main.cc
+++ b/src/main.cc
@@ -11,7 +11,7 @@
 #include "mesh.h"
 #include "hair.h"
 
-#define MAX_NUM_SPAWNS 4
+#define MAX_NUM_SPAWNS 400
 #define THRESH 0.5
 
 static bool init();
@@ -120,6 +120,11 @@ static void cleanup()
 
 static void display()
 {
+	static unsigned long prev_time;
+	unsigned long msec = glutGet(GLUT_ELAPSED_TIME);
+	float dt = (float)(msec - prev_time) / 1000.0;
+	prev_time = msec;
+
 	glClear(GL_COLOR_BUFFER_BIT | GL_DEPTH_BUFFER_BIT);
 
 	head_xform = Mat4::identity;
@@ -131,14 +136,16 @@ static void display()
 	glTranslatef(0, 0, -cam_dist);
 	glRotatef(cam_phi, 1, 0, 0);
 	glRotatef(cam_theta, 0, 1, 0);
-
+	/* multiplying with the head rot matrix */
+	glPushMatrix();
 	glMultMatrixf(head_xform[0]);
-
 	for(size_t i=0; i<meshes.size(); i++) {
 		meshes[i]->draw();
 	}
+	glPopMatrix();
 
 	hair.set_transform(head_xform);
+	hair.update(dt);
 	hair.draw();
 
 	glutSwapBuffers();
@@ -211,7 +218,7 @@ static void motion(int x, int y)
 			if(head_rx > 45) head_rx = 45;
 
 			if(head_rz < -90) head_rz = -90;
-			if(head_rz > 90) head_rx = 90;
+			if(head_rz > 90) head_rz = 30;
 		}
 	}
 	else {
-- 
1.7.10.4