made videos links prettier

god github's video thing is scuffed...

README.md

@@ -0,0 +1,70 @@
+# From Flying Balls to Colliding Polygons
+
+## Table of contents
+
+- [Abstract](#abstract)
+- [Before vs After](#before-vs-after)
+  - [Context](#context)
+  - [Before](#before)
+  - [After](#after)
+- [Contact](#contact)
+
+## Abstract
+
+> (text taken from the abstract of my report that you can find
+> [here](https://github.com/karma-riuk/bachelor-project-report/blob/main/bachelorproject.pdf)
+
+Physics engines are a fun and interesting way to learn about the laws of
+physics, as well as computer science. They provide a real-time simulation of
+common physical phenomena, and therefore illustrate theoretical concepts such as
+the equations that dictate the motion of objects.
+
+The goal of this project was to extend an existing physics engine built for
+demonstration purposes. This engine was initially designed and developed to
+simulate circular objects ("balls") in 2D.
+
+With this project, we intended to extend this engine to also simulate arbitrary
+polygons, again in a physically accurate way. The main technical challenges of
+the project is therefore the correct simulation of the dynamics of rigid,
+polygonal objects. In particular, we developed a model of polygonal rigid
+objects:
+
+- we implemented a simulation of their inertial motion, possibly in the
+  presence of a constant force field such as gravity;
+- we detect collisions between objects;
+- we compute and then simulate the dynamic effects of collisions.
+
+The simulations are animated and displayed in real-time. It is also therefore
+crucial that the simulation code be efficient to obtain smooth animations.
+
+## Before vs After
+
+### Context
+
+A little of context for the follow videos:
+
+- in the first video, the special ball with an arrow inside is a "spaceship",
+  that can be controlled by the user;
+- the yellow bar that appears after midway through both videos represent the
+  restitution coefficient of the collision resolution (the lower it is, the
+  greater the dampening on impact between objects);
+- the white line with a ball at the end that appears after the restitution
+  coefficient bar represents the gravity vector that gets applied to the speed
+  of each object at each frame, the ball is the direction the vector is pointing
+  it.
+
+### Before
+
+[before](https://github.com/karma-riuk/flying-balls/assets/30158492/ddc0d608-9667-4a21-8132-e056e443e0e2)
+
+### After
+
+[after](https://github.com/karma-riuk/flying-balls/assets/30158492/bd4013b8-bc01-4d52-aa2f-44dbc25de717)
+
+<!-- ## Controls -->
+<!---->
+<!-- ## Installation -->
+
+## Contact
+
+If you have any question concerning this work, feel free to contact me at [arno.fauconnet@gmail.com](mailto:arno.fauconnet@gmail.com)

game.h

@@ -13,8 +13,8 @@ extern double delta; /* simulation time delta in seconds */
 extern int width;  /* game canvas width */
 extern int height; /* game canvas height */
 
-#define DEFAULT_WIDTH 800
-#define DEFAULT_HEIGHT 800
+#define DEFAULT_WIDTH 1000
+#define DEFAULT_HEIGHT 1000
 
 extern GtkWidget* canvas; /* game canvas object */
 

polygons.cc

@@ -14,7 +14,7 @@
 #include <utility>
 
 #define ARROW_VAL_RATIO 1.7
-
+#define SUBSETPS 5
 
 bool draw_speed = true;
 
@@ -35,6 +35,21 @@ static double random_color_component() {
     return 1.0 * (rand() % 200 + 56) / 255;
 };
 
+static vec2d random_velocity() {
+    double r2;
+    vec2d v;
+    do {
+        v.x = v_min + rand() % (v_max + 1 - v_min);
+        v.y = v_min + rand() % (v_max + 1 - v_min);
+        r2 = vec2d::dot(v, v);
+    } while (r2 > v_max * v_max || r2 < v_min * v_min);
+    if (rand() % 2)
+        v.x = -v.x;
+    if (rand() % 2)
+        v.y = -v.y;
+    return v;
+}
+
 void polygons_init_state() {
     n_polygons = 20;
     polygons = new polygon[n_polygons];
@@ -68,7 +83,6 @@ void polygons_init_state() {
                         .set_center({width / 2., height - height / 17.})
                         .set_angle(45);
 
-
     // ---------- Shapes flying around start here ----------
     polygons[n++] = poly_generate::regular(100, 3)
                         .set_center({100, 400})
@@ -88,9 +102,14 @@ void polygons_init_state() {
                         .set_speed({10, 0});
 
     polygons[n++] = poly_generate::rectangle(100, 150).set_center({600, 200});
+
+    polygons[n++] = poly_generate::regular(72, 8)
+                        .set_center({500, 500})
+                        .set_speed({100, 0});
+
     polygons[n++] = poly_generate::regular(50, 5)
                         .set_center({150, 150})
-                        .set_speed({100, 0});
+                        .set_speed({150, 0});
 
     polygons[n++] = poly_generate::general({{40, 20},
                                             {40, 40},
@@ -232,19 +251,24 @@ static void check_collisions(polygon* current_p) {
 }
 
 void polygons_update_state() {
+    const static float sub_delta = delta / SUBSETPS;
+
+    for (uint i = SUBSETPS; i--;) {
         for (polygon* p = polygons; p != polygons + n_polygons; ++p) {
-        if (p->mass == INFINITY) // immovable objects don't need to be updated
+            // immovable objects don't need to be updated
+            if (p->mass == INFINITY)
                 continue;
             check_collisions(p);
 
-        p->rotate(delta * p->angular_speed);
+            p->rotate(sub_delta * p->angular_speed);
             p->angle = std::fmod(p->angle, 360);
 
-        p->translate(delta * p->speed);
+            p->translate(sub_delta * p->speed);
 
             vec2d g = gravity_vector(p);
-        p->translate(.5 * delta * delta * g);
-        p->speed += delta * g;
+            p->translate(.5 * sub_delta * sub_delta * g);
+            p->speed += sub_delta * g;
+        }
     }
 }
 
@@ -308,7 +332,6 @@ void polygon::draw(cairo_t* cr) const {
     vec2d centroid = this->centroid();
     draw_circle(cr, centroid, 1);
 
-
     // draw speed
     if (draw_speed && this->mass != INFINITY) {
         hsv_t hsv = rgb2hsv(this->color);