Add String constraints and redo the grid with strings instead.

1 files changed, 82 insertions, 19 deletions

diff --git a/akamaru.c b/akamaru.c
index 8fa2ec0..fe14d20 100644
--- a/akamaru.c
+++ b/akamaru.c
@@ -35,6 +35,7 @@ struct _xy_pair {
 
 typedef struct _Object Object;
 typedef struct _Stick Stick;
+typedef struct _String String;
 typedef struct _Offset Offset;
 typedef struct _Model Model;
 
@@ -54,6 +55,11 @@ struct _Stick {
   int length;
 };
 
+struct _String {
+  Object *a, *b;
+  int length;
+};
+
 struct _Offset {
   Object *a, *b;
   int dx, dy;
@@ -64,6 +70,8 @@ struct _Model {
   Object *objects;
   int num_sticks;
   Stick *sticks;
+  int num_strings;
+  String *strings;
   int num_offsets;
   Offset *offsets;
   double k;
@@ -86,6 +94,9 @@ model_init_snake (Model *model)
   model->num_objects = num_objects;
   model->sticks = g_new (Stick, num_sticks);
   model->num_sticks = num_sticks;
+  model->strings = NULL;
+  model->num_strings = 0;
+  model->offsets = NULL;
   model->num_offsets = 0;
 
   for (i = 0; i < num_objects; i++) {
@@ -121,6 +132,8 @@ model_init_rope (Model *model)
   model->num_objects = num_objects;
   model->sticks = g_new (Stick, num_sticks);
   model->num_sticks = num_sticks;
+  model->strings = NULL;
+  model->num_strings = 0;
   model->offsets = NULL;
   model->num_offsets = 0;
 
@@ -156,6 +169,8 @@ model_init_curtain (Model *model)
   model->num_objects = num_objects;
   model->sticks = g_new (Stick, num_sticks);
   model->num_sticks = num_sticks;
+  model->strings = NULL;
+  model->num_strings = 0;
   model->offsets = g_new (Offset, num_ropes - 1);
   model->num_offsets = num_ropes - 1;
 
@@ -191,27 +206,29 @@ model_init_curtain (Model *model)
 static void
 model_init_grid (Model *model)
 {
-  const int num_ropes = 15;
-  const int num_rope_objects = 15;
+  const int num_ropes = 4;
+  const int num_rope_objects = 4;
   const int num_objects = num_ropes * num_rope_objects;
-  const int num_sticks = num_ropes * (num_rope_objects - 1) +
+  const int num_strings = num_ropes * (num_rope_objects - 1) +
     (num_ropes - 1) * num_rope_objects;
-  const int stick_length = 10;
-  const int rope_offset = 10;
+  const int string_length = 30;
+  const int rope_offset = 30;
   double x, y;
-  int i, j, index, stick_index;
+  int i, j, index, string_index;
 
   model->objects = g_new (Object, num_objects);
   model->num_objects = num_objects;
-  model->sticks = g_new (Stick, num_sticks);
-  model->num_sticks = num_sticks;
+  model->sticks = NULL;
+  model->num_sticks = 0;
+  model->strings = g_new (String, num_strings);
+  model->num_strings = num_strings;
   model->offsets = g_new (Offset, num_ropes - 1);
   model->num_offsets = num_ropes - 1;
 
   for (i = 0; i < num_ropes; i++) {
     for (j = 0; j < num_rope_objects; j++) {
       x = 200 + i * rope_offset;
-      y = 40 + j * stick_length;
+      y = 40 + j * string_length;
       index = i * num_rope_objects + j;
       model->objects[index].position.x = x;
       model->objects[index].position.y = y;
@@ -219,18 +236,18 @@ model_init_grid (Model *model)
       model->objects[index].previous_position.y = y;
 
       if (i + 1 < num_ropes) {
-	stick_index = i * num_rope_objects + j;
-	model->sticks[stick_index].a = &model->objects[index];
-	model->sticks[stick_index].b = &model->objects[index + num_rope_objects];
-	model->sticks[stick_index].length = stick_length;
+	string_index = i * num_rope_objects + j;
+	model->strings[string_index].a = &model->objects[index];
+	model->strings[string_index].b = &model->objects[index + num_rope_objects];
+	model->strings[string_index].length = string_length;
       }
 
       if (j + 1 < num_rope_objects) {
-	stick_index =
+	string_index =
 	  (num_ropes - 1) * num_rope_objects + i * (num_rope_objects - 1) + j;
-	model->sticks[stick_index].a = &model->objects[index];
-	model->sticks[stick_index].b = &model->objects[index + 1];
-	model->sticks[stick_index].length = stick_length;
+	model->strings[string_index].a = &model->objects[index];
+	model->strings[string_index].b = &model->objects[index + 1];
+	model->strings[string_index].length = string_length;
       }
     }
 
@@ -254,6 +271,9 @@ model_fini (Model *model)
   g_free (model->sticks);
   model->sticks = NULL;
   model->sticks = 0;
+  g_free (model->strings);
+  model->strings = NULL;
+  model->strings = 0;
   g_free (model->offsets);
   model->offsets = NULL;
   model->num_offsets = 0;
@@ -266,7 +286,7 @@ model_accumulate_forces (Model *model)
 
   for (i = 0; i < model->num_objects; i++) {
     model->objects[i].force.x = 0;
-    model->objects[i].force.y = 2;
+    model->objects[i].force.y = 3;
   }
 }
 
@@ -350,6 +370,22 @@ model_constrain (Model *model, double step)
     model->offsets[i].b->position.y = y + model->offsets[i].dy / 2;
   }
 
+  /* String constraints. */
+  for (i = 0; i < model->num_strings; i++) {
+    x = model->strings[i].a->position.x;
+    y = model->strings[i].a->position.y;
+    dx = model->strings[i].b->position.x - x;
+    dy = model->strings[i].b->position.y - y;
+    distance = sqrt (dx * dx + dy * dy);
+    if (distance < model->strings[i].length)
+      continue;
+    fraction = (distance - model->strings[i].length) / distance / 2;
+    model->strings[i].a->position.x = x + dx * fraction;
+    model->strings[i].a->position.y = y + dy * fraction;
+    model->strings[i].b->position.x = x + dx * (1 - fraction);
+    model->strings[i].b->position.y = y + dy * (1 - fraction);
+  }
+
 #if 1
   /* Stick constraints. */
   for (i = 0; i < model->num_sticks; i++) {
@@ -390,7 +426,7 @@ model_step (Model *model, double delta_t)
   model_accumulate_forces (model);
   model_integrate (model, delta_t);
 
-  for (i = 0; i < 15; i++)
+  for (i = 0; i < 35; i++)
     model_constrain (model, delta_t);
 
   model->theta += delta_t;
@@ -456,6 +492,31 @@ draw_sticks (cairo_t *cr,
 }
 
 static void
+draw_strings (cairo_t *cr,
+	      Model   *model,
+	      Color   *color)
+{
+  int i;
+
+  cairo_set_source_rgba (cr, color->red, color->green, color->blue, 1);
+  cairo_new_path (cr);
+  cairo_set_line_width (cr, 1);
+  cairo_set_line_join (cr, CAIRO_LINE_JOIN_ROUND);
+  cairo_set_line_cap (cr, CAIRO_LINE_CAP_ROUND);
+
+  for (i = 0; i < model->num_strings; i++) {
+    cairo_move_to (cr,
+		   model->strings[i].a->position.x,
+		   model->strings[i].a->position.y);
+    cairo_line_to (cr,
+		   model->strings[i].b->position.x,
+		   model->strings[i].b->position.y);
+  }
+
+  cairo_stroke (cr);
+}
+
+static void
 draw_offsets (cairo_t *cr,
 	      Model   *model,
 	      Color   *color)
@@ -512,6 +573,7 @@ draw_objects (cairo_t *cr, Model *model, Color *color)
 }
 
 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 };
@@ -531,6 +593,7 @@ expose_event (GtkWidget      *widget,
 
   draw_constraints (cr, model, &red);
   draw_sticks (cr, model, &black);
+  draw_strings (cr, model, &green);
   draw_offsets (cr, model, &blue);
   draw_objects (cr, model, &white);