From a65a977df6fa8fee831c91cdc754d62e023b6630 Mon Sep 17 00:00:00 2001
From: Eleni Maria Stea <estea@igalia.com>
Date: Sat, 26 Jan 2019 20:29:25 +0200
Subject: [PATCH] Failed hack for collision detection with a sphere.

---
 src/hair.cc   |   24 +++++++++++++++++++++++-
 src/hair.h    |    4 ++++
 src/main.cc   |   36 ++++++++++++++++++++++++++++++++++++
 src/object.cc |   16 ++++++++++++++++
 src/object.h  |   17 +++++++++++++++++
 5 files changed, 96 insertions(+), 1 deletion(-)
 create mode 100644 src/object.cc
 create mode 100644 src/object.h

diff --git a/src/hair.cc b/src/hair.cc
index c86044b..b99d133 100644
--- a/src/hair.cc
+++ b/src/hair.cc
@@ -185,8 +185,30 @@ void Hair::update(float dt)
 
 		Vec3 accel = force; /* mass 1 */
 		hair[i].velocity += ((-hair[i].velocity * DAMPING) + accel) * dt;
-		hair[i].pos += hair[i].velocity * dt;
+		Vec3 new_pos = hair[i].pos + hair[i].velocity * dt;
+
+		hair[i].pos = handle_collision(new_pos);
 
 		dbg_force = force;
 	}
 }
+
+void Hair::add_collider(CollSphere *cobj) {
+	colliders.push_back(cobj);
+}
+
+Vec3 Hair::handle_collision(const Vec3 &v) const
+{
+	/* if we transform the center and the radius of the collider sphere
+	 * we might end up with a spheroid, so better just multiply the 
+	 * position with the inverse transform before check for collisions :*/
+
+	Vec3 new_v = inverse(xform) * v;
+
+	for(size_t i=0; i<colliders.size(); i++) {
+		if(colliders[i]->contains(new_v)) {
+			new_v = colliders[i]->project_surf(new_v);
+		}
+	}
+	return xform * new_v;
+}
diff --git a/src/hair.h b/src/hair.h
index 5ef54d0..9ef5130 100644
--- a/src/hair.h
+++ b/src/hair.h
@@ -4,6 +4,7 @@
 #include <gmath/gmath.h>
 
 #include "mesh.h" 
+#include "object.h"
 
 struct HairStrand {
 	Vec3 pos;
@@ -17,6 +18,7 @@ private:
 	float hair_length;
 	std::vector<HairStrand> hair;
 	Mat4 xform;
+	std::vector<CollSphere *> colliders;
 
 public:
 	Hair();
@@ -27,6 +29,8 @@ public:
 
 	void set_transform(Mat4 &xform);
 	void update(float dt);
+	void add_collider(CollSphere *cobj);
+	Vec3 handle_collision(const Vec3 &v) const;
 };
 
 #endif //PARTICLES_H_
diff --git a/src/main.cc b/src/main.cc
index 54959a8..01f6716 100644
--- a/src/main.cc
+++ b/src/main.cc
@@ -10,6 +10,7 @@
 
 #include "mesh.h"
 #include "hair.h"
+#include "object.h"
 
 #define MAX_NUM_SPAWNS 400
 #define THRESH 0.5
@@ -32,6 +33,7 @@ static int win_width, win_height;
 static float cam_theta, cam_phi = 25, cam_dist = 8;
 static float head_rz, head_rx; /* rot angles x, z axis */
 static Mat4 head_xform;
+static CollSphere coll_sphere; /* sphere used for collision detection */
 
 int main(int argc, char **argv)
 {
@@ -103,11 +105,16 @@ static bool init()
 		return false;
 	}
 
+	coll_sphere.radius = 1.0;
+	coll_sphere.center = Vec3(0, 0.6, 0.53);
+
 	if(!hair.init(mesh_head, MAX_NUM_SPAWNS, THRESH)) {
 		fprintf(stderr, "Failed to initialize hair\n");
 		return false;
 	}
 
+	hair.add_collider(&coll_sphere);
+
 	return true;
 }
 
@@ -139,15 +146,44 @@ static void display()
 	/* multiplying with the head rot matrix */
 	glPushMatrix();
 	glMultMatrixf(head_xform[0]);
+	glPushAttrib(GL_LINE_BIT);
+	glLineWidth(1);
+	glPolygonMode(GL_FRONT_AND_BACK, GL_LINE);
 	for(size_t i=0; i<meshes.size(); i++) {
 		meshes[i]->draw();
 	}
+	glPolygonMode(GL_FRONT_AND_BACK, GL_FILL);
+	glPopAttrib();
+
 	glPopMatrix();
 
 	hair.set_transform(head_xform);
 	hair.update(dt);
 	hair.draw();
 
+/*
+	glPushAttrib(GL_ENABLE_BIT);
+	glDisable(GL_DEPTH_TEST);
+	glDisable(GL_LIGHTING);
+	glBegin(GL_POINTS);
+	for (int i=0; i<500; i++) {
+		Vec3 p;
+		p.x = (float)rand() / RAND_MAX * 8 - 4;
+		p.y = (float)rand() / RAND_MAX * 4;
+		p.z = 0;
+
+		Vec3 tmp = inverse(head_xform) * p;
+		if(coll_sphere.contains(tmp)) {
+			glColor3f(1, 0, 0);
+		}
+		else glColor3f(0, 1, 0);
+
+		glVertex3f(p.x, p.y, p.z);
+	}
+	glEnd();
+	glPopAttrib();
+	*/
+
 	glutSwapBuffers();
 	assert(glGetError() == GL_NO_ERROR);
 }
diff --git a/src/object.cc b/src/object.cc
new file mode 100644
index 0000000..ae33bb1
--- /dev/null
+++ b/src/object.cc
@@ -0,0 +1,16 @@
+#include "object.h"
+
+CollSphere::CollSphere()
+{
+	radius = 1.0;
+}
+
+bool CollSphere::contains(const Vec3 &v) const
+{
+	return length_sq(v - center) <= radius * radius;
+}
+
+Vec3 CollSphere::project_surf(const Vec3 &v) const
+{
+	return center + normalize(v - center) * radius;
+}
diff --git a/src/object.h b/src/object.h
new file mode 100644
index 0000000..2efedf7
--- /dev/null
+++ b/src/object.h
@@ -0,0 +1,17 @@
+#ifndef OBJECT_H_
+#define OBJECT_H_
+
+#include <gmath/gmath.h>
+
+class CollSphere {
+public:
+	float radius;
+	Vec3 center;
+
+	CollSphere();
+
+	bool contains(const Vec3 &v) const;
+	Vec3 project_surf(const Vec3 &v) const;
+};
+
+#endif // OBJECT_H_
-- 
1.7.10.4