From ed91d376224c1efe305d483c05f837820df75b71 Mon Sep 17 00:00:00 2001
From: Eleni Maria Stea <estea@igalia.com>
Date: Wed, 21 Nov 2018 16:42:53 +0200
Subject: [PATCH] Added anchor points and hair strands.

---
 Makefile    |    2 +-
 src/hair.cc |   68 +++++++++++++++++++++++++++++++++++++++++++++++++----------
 src/hair.h  |   13 ++++++++++--
 src/main.cc |    5 +++--
 4 files changed, 72 insertions(+), 16 deletions(-)

diff --git a/Makefile b/Makefile
index 517443a..660400a 100755
--- a/Makefile
+++ b/Makefile
@@ -10,7 +10,7 @@ inc = -Isrc -Isrc/shaders -Isrc/math
 
 CXX = g++
 CXXFLAGS = -pedantic -Wall $(dbg) $(opt) $(inc)
-LDFLAGS = -lGL -lGLU -lglut -lGLEW -limago -lassimp
+LDFLAGS = -lGL -lGLU -lglut -lGLEW -limago -lassimp -lgmath
 
 $(bin): $(obj)
 	$(CXX) -o $@ $(obj) $(LDFLAGS)
diff --git a/src/hair.cc b/src/hair.cc
index 33bdd0d..171c7e8 100644
--- a/src/hair.cc
+++ b/src/hair.cc
@@ -13,8 +13,14 @@ struct Triangle {
 	Vec3 n[3];
 };
 
-Hair::Hair() {}
-Hair::~Hair() {}
+Hair::Hair()
+{
+	hair_length = 0.5;
+}
+
+Hair::~Hair()
+{
+}
 
 static Vec3 calc_rand_point(const Triangle &tr, Vec3 *bary)
 {
@@ -34,7 +40,6 @@ static Vec3 calc_rand_point(const Triangle &tr, Vec3 *bary)
 	bary->y = v;
 	bary->z = c;
 
-//	printf("u %f v %f c %f sum: %f\n", u, v, c, u+v+c);
 	return rp;
 }
 
@@ -104,28 +109,69 @@ bool Hair::init(const Mesh *m, int max_num_spawns, float thresh)
 				continue;
 		}
 
+		HairStrand strand;
 		/* weighted sum of the triangle's vertex normals */
-		Vec3 spawn_dir = rtriangle.n[0] * bary.x + rtriangle.n[1] * bary.y + rtriangle.n[2] * bary.z;
-		spawn_directions.push_back(normalize(spawn_dir));
-		spawn_points.push_back(rpoint);
+		strand.spawn_dir = normalize(rtriangle.n[0] * bary.x + rtriangle.n[1] * bary.y + rtriangle.n[2] * bary.z);
+		strand.spawn_pt = rpoint;
+		hair.push_back(strand);
+
 		kd_insert3f(kd, rpoint.x, rpoint.y, rpoint.z, 0);
 	}
 
 	kd_free(kd);
+
+	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);
+		if(fabs(vk.x > 0.99)) {
+			vi = Vec3(0, -1, 0);
+		}
+		Vec3 vj = normalize(cross(vk, vi));
+		vi = cross(vj, vk);
+
+		/* identity when the hair points to the z axis */
+		Mat4 basis = Mat4(vi, vj, vk);
+
+		for(int j=0; j<3; j++) {
+			float angle = (float)j / 3.0 * 2 * M_PI;
+			/* dir of each anchor relative to hair end */
+			Vec3 dir = Vec3(cos(angle), sin(angle), 0);
+			dir = basis * dir;
+			hair[i].anchor_dirs[j] = hair[i].pos + dir - hair[i].spawn_pt;
+		}
+	}
 	return true;
 }
 
 void Hair::draw() const
 {
 	glPushAttrib(GL_ENABLE_BIT);
-	glDisable(GL_DEPTH_TEST);
+//	glDisable(GL_DEPTH_TEST);
 	glDisable(GL_LIGHTING);
-	glPointSize(2);
+	glPointSize(5);
+	glLineWidth(2);
+
+	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;
+		glVertex3f(p.x, p.y, p.z);
+	}
+	glEnd();
+
 	glBegin(GL_POINTS);
-	for(size_t i = 0; i < spawn_points.size(); i++) {
-		glColor3f(1, 1, 0);
-		glVertex3f(spawn_points[i].x, spawn_points[i].y, spawn_points[i].z);
+	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);
+		}
 	}
 	glEnd();
+
 	glPopAttrib();
 }
diff --git a/src/hair.h b/src/hair.h
index 19fa82e..be979ee 100644
--- a/src/hair.h
+++ b/src/hair.h
@@ -5,10 +5,19 @@
 
 #include "mesh.h" 
 
+struct HairStrand {
+	Vec3 pos;
+	Vec3 velocity;
+	/* directions relative to the spawn point */
+	Vec3 anchor_dirs[3];
+	Vec3 spawn_pt;
+	Vec3 spawn_dir;
+};
+
 class Hair {
 private:
-	std::vector<Vec3> spawn_points;
-	std::vector<Vec3> spawn_directions;
+	float hair_length;
+	std::vector<HairStrand> hair;
 
 public:
 	Hair();
diff --git a/src/main.cc b/src/main.cc
index 750a2d8..2bdbad9 100644
--- a/src/main.cc
+++ b/src/main.cc
@@ -9,7 +9,8 @@
 #include "mesh.h"
 #include "hair.h"
 
-#define MAX_NUM_SPAWNS 500
+#define MAX_NUM_SPAWNS 4
+#define THRESH 0.5
 
 static bool init();
 static void cleanup();
@@ -90,7 +91,7 @@ static bool init()
 		return false;
 	}
 
-	if(!hair.init(mesh_head, MAX_NUM_SPAWNS, 0.1)) {
+	if(!hair.init(mesh_head, MAX_NUM_SPAWNS, THRESH)) {
 		fprintf(stderr, "Failed to initialize hair\n");
 		return false;
 	}
-- 
1.7.10.4