Add spring forces.

1 files changed, 99 insertions, 6 deletions

diff --git a/akamaru.c b/akamaru.c
index b26adea..17c70e9 100644
--- a/akamaru.c
+++ b/akamaru.c
@@ -38,6 +38,7 @@ struct _xy_pair {
 typedef struct _Object Object;
 typedef struct _Stick Stick;
 typedef struct _String String;
+typedef struct _Spring Spring;
 typedef struct _Polygon Polygon;
 typedef struct _Offset Offset;
 typedef struct _Model Model;
@@ -69,6 +70,11 @@ struct _Offset {
   int dx, dy;
 };
 
+struct _Spring {
+  Object *a, *b;
+  int length;
+};
+
 struct _Polygon {
   int num_points;
   Point *points;
@@ -85,6 +91,8 @@ struct _Model {
   String *strings;
   int num_offsets;
   Offset *offsets;
+  int num_springs;
+  Spring *springs;
   int num_polygons;
   Polygon *polygons;
   double k;
@@ -184,6 +192,7 @@ model_init_snake (Model *model)
     model->objects[i].position.y = random() % 200 + 20;
     model->objects[i].previous_position.x = random() % 200 + 20;
     model->objects[i].previous_position.y = random() % 200 + 20;
+    model->objects[i].mass = 1;
 
     if (i + 1 < num_objects) {
       model->sticks[i * 2].a = &model->objects[i];
@@ -220,6 +229,7 @@ model_init_rope (Model *model)
     model->objects[i].position.y = 40 + i * stick_length;
     model->objects[i].previous_position.x = 200;
     model->objects[i].previous_position.y = 40 + i * stick_length;
+    model->objects[i].mass = 1;
 
     if (i + 1 < num_objects) {
       model->sticks[i].a = &model->objects[i];
@@ -266,6 +276,7 @@ model_init_curtain (Model *model)
       model->objects[index].position.y = y;
       model->objects[index].previous_position.x = x;
       model->objects[index].previous_position.y = y;
+      model->objects[i].mass = 1;
 
       if (j + 1 < num_rope_objects) {
 	stick_index = i * (num_rope_objects - 1) + j;
@@ -317,6 +328,7 @@ model_init_grid (Model *model)
       model->objects[index].position.y = y;
       model->objects[index].previous_position.x = x;
       model->objects[index].previous_position.y = y;
+      model->objects[index].mass = 1;
 
       if (i + 1 < num_ropes) {
 	string_index = i * num_rope_objects + j;
@@ -341,6 +353,39 @@ model_init_grid (Model *model)
 }
 
 static void
+model_init_molecule (Model *model)
+{
+  const int num_objects = 8;
+  const int num_springs = num_objects * 2;
+  const int spring_length = 50;
+  int i;
+
+  memset (model, 0, sizeof *model);
+  model->objects = g_new (Object, num_objects);
+  model->num_objects = num_objects;
+  model->springs = g_new (Spring, num_springs);
+  model->num_springs = num_springs;
+  model->k = 0.2;
+
+  for (i = 0; i < num_objects; i++) {
+    model->objects[i].position.x = 200 + i * 20;
+    model->objects[i].position.y = 200;
+    model->objects[i].previous_position.x = 200 + i * 20;
+    model->objects[i].previous_position.y = 200;
+    model->objects[i].mass = 0;
+  }
+
+  for (i = 0; i < num_objects; i++) {
+    model->springs[i * 2].a = &model->objects[i];
+    model->springs[i * 2].b = &model->objects[(i + 1) % num_objects];
+    model->springs[i * 2].length = spring_length;
+    model->springs[i * 2 + 1].a = &model->objects[i];
+    model->springs[i * 2 + 1].b = &model->objects[(i + 2) % num_objects];
+    model->springs[i * 2 + 1].length = spring_length;
+  }
+}
+
+static void
 model_fini (Model *model)
 {
   g_free (model->objects);
@@ -354,10 +399,27 @@ static void
 model_accumulate_forces (Model *model)
 {
   int i;
+  double x, y, dx, dy, distance, displacement;
+  Vector u;
 
   for (i = 0; i < model->num_objects; i++) {
     model->objects[i].force.x = 0;
-    model->objects[i].force.y = 3;
+    model->objects[i].force.y = 3 * model->objects[i].mass;
+  }
+
+  for (i = 0; i < model->num_springs; i++) {
+    x = model->springs[i].a->position.x;
+    y = model->springs[i].a->position.y;
+    dx = model->springs[i].b->position.x - x;
+    dy = model->springs[i].b->position.y - y;
+    distance = sqrt (dx * dx + dy * dy);
+    u.x = dx / distance;
+    u.y = dy / distance;
+    displacement = distance - model->springs[i].length;
+    model->springs[i].a->force.x += u.x * model->k * displacement;
+    model->springs[i].a->force.y += u.y * model->k * displacement;
+    model->springs[i].b->force.x -= u.x * model->k * displacement;
+    model->springs[i].b->force.y -= u.y * model->k * displacement;
   }
 }
 
@@ -374,9 +436,9 @@ model_integrate (Model *model, double step)
     y = o->position.y;
     
     o->position.x =
-      x + 0.9 * (x - o->previous_position.x) + o->force.x * step * step;
+      x + 0.8 * (x - o->previous_position.x) + o->force.x * step * step;
     o->position.y =
-      y + 0.9 * (y - o->previous_position.y) + o->force.y * step * step;
+      y + 0.8 * (y - o->previous_position.y) + o->force.y * step * step;
 
     o->previous_position.x = x;
     o->previous_position.y = y;
@@ -663,6 +725,31 @@ draw_offsets (cairo_t *cr,
 }
 
 static void
+draw_springs (cairo_t *cr,
+	      Model   *model,
+	      Color   *color)
+{
+  int i;
+
+  cairo_set_source_rgba (cr, color->red, color->green, color->blue, 0.4);
+  cairo_new_path (cr);
+  cairo_set_line_width (cr, 2);
+  cairo_set_line_join (cr, CAIRO_LINE_JOIN_ROUND);
+  cairo_set_line_cap (cr, CAIRO_LINE_CAP_ROUND);
+
+  for (i = 0; i < model->num_springs; i++) {
+    cairo_move_to (cr,
+		   model->springs[i].a->position.x,
+		   model->springs[i].a->position.y);
+    cairo_line_to (cr,
+		   model->springs[i].b->position.x,
+		   model->springs[i].b->position.y);
+  }
+
+  cairo_stroke (cr);
+}
+
+static void
 draw_polygons (cairo_t *cr, Model *model, Color *color)
 {
   Polygon *p;
@@ -686,7 +773,12 @@ draw_objects (cairo_t *cr, Model *model, Color *color)
 {
   int i;
 
+  cairo_set_source_rgba (cr, color->red, color->green, color->blue, 0.4);
   for (i = 0; i < model->num_objects; i++) {
+    cairo_arc (cr, model->objects[i].position.x,
+	       model->objects[i].position.y,
+	       3, 0, 2*M_PI);
+    cairo_fill (cr);
   }
 }
 
@@ -694,7 +786,6 @@ static Color blue = { 0, 0, 1 };
 static Color green = { 0, 1, 0 };
 static Color red = { 1, 0, 0 };
 static Color black = { 0, 0, 0 };
-static Color white = { 1, 1, 1 };
 
 typedef struct _Closure Closure;
 struct _Closure {
@@ -719,8 +810,9 @@ draw_model (GtkWidget *widget, Model *model)
   draw_polygons (cr, model, &blue);
   draw_sticks (cr, model, &black);
   draw_strings (cr, model, &green);
+  draw_springs (cr, model, &black);
   draw_offsets (cr, model, &blue);
-  draw_objects (cr, model, &white);
+  draw_objects (cr, model, &red);
 
   cairo_destroy (cr);
 }
@@ -818,7 +910,8 @@ create_model_store (void)
     { "Rope", model_init_rope },
     { "Snake", model_init_snake },
     { "Curtain", model_init_curtain },
-    { "Grid", model_init_grid }
+    { "Grid", model_init_grid },
+    { "Molecule", model_init_molecule }
   };
 
   GtkTreeIter iter;