Implement general polygon constraints.

Also, replace ad-hoc ledge and ground constraints with polygons.

1 files changed, 175 insertions, 79 deletions

diff --git a/akamaru.c b/akamaru.c
index 14d0601..af0a0f1 100644
--- a/akamaru.c
+++ b/akamaru.c
@@ -11,8 +11,10 @@
  *
  * TODO:
  *
- *     - Add code to add boxes
- *     - Add circle object
+ * - Add code to add boxes
+ * - Add circle object
+ * - Try out this idea: make constraint solver take mean of all
+ *   corrections at the end instead of meaning as it goes.
  */
 
 #include <gtk/gtk.h>
@@ -20,6 +22,7 @@
 #include <cairo-xlib.h>
 #include <gdk/gdkx.h>
 #include <stdlib.h>
+#include <string.h>
 #include <sys/time.h>
 #include <math.h>
 
@@ -37,6 +40,7 @@ struct _xy_pair {
 typedef struct _Object Object;
 typedef struct _Stick Stick;
 typedef struct _String String;
+typedef struct _Polygon Polygon;
 typedef struct _Offset Offset;
 typedef struct _Model Model;
 
@@ -66,6 +70,13 @@ struct _Offset {
   int dx, dy;
 };
 
+struct _Polygon {
+  int num_points;
+  Point *points;
+  Vector *normals;
+  int edge;
+};
+
 struct _Model {
   int num_objects;
   Object *objects;
@@ -75,6 +86,8 @@ struct _Model {
   String *strings;
   int num_offsets;
   Offset *offsets;
+  int num_polygons;
+  Polygon *polygons;
   double k;
   double friction;
 
@@ -85,20 +98,87 @@ struct _Model {
 };
 
 static void
+polygon_init (Polygon *p, int num_points, ...)
+{
+  double dx, dy, length;
+  int i, j;
+  va_list ap;
+
+  /* Polygons are defined counter-clock-wise in a coordinate system
+   * with the y-axis pointing down. */
+
+  va_start (ap, num_points);
+  p->num_points = num_points;
+  p->points = g_new (Point, num_points);
+
+  for (i = 0; i < num_points; i++) {
+    p->points[i].x = va_arg (ap, double);
+    p->points[i].y = va_arg (ap, double);
+  }
+  va_end (ap);
+  
+  p->normals = g_new (Vector, p->num_points);
+  /* Compute outward pointing normals.  p->normals[i] is the normal
+   * for the edged between p->points[i] and p->points[i + 1]. */
+ for (i = 0; i < p->num_points; i++) {
+    j = (i + 1) % p->num_points;
+    dx = p->points[j].x - p->points[i].x;
+    dy = p->points[j].y - p->points[i].y;
+    length = sqrt (dx * dx + dy * dy);
+    p->normals[i].x = -dy / length;
+    p->normals[i].y = dx / length;
+  }
+}
+
+static void
+polygon_init_diamond (Polygon *polygon, double x, double y)
+{
+  return polygon_init (polygon, 5, 
+		       x, y, 
+		       x + 10, y + 40,
+		       x + 90, y + 40,
+		       x + 100, y,
+		       x + 50, y - 20);
+}
+
+static void
+polygon_init_rectangle (Polygon *polygon, double x0, double y0,
+			double x1, double y1)
+{
+  return polygon_init (polygon, 4, x0, y0, x0, y1, x1, y1, x1, y0);
+}
+
+static void
+model_init_polygons (Model *model)
+{
+  const int num_polygons = 5;
+
+  model->polygons = g_new (Polygon, num_polygons);
+  polygon_init_diamond (&model->polygons[0], 250, 300);
+  polygon_init_diamond (&model->polygons[1], 400, 150);
+  polygon_init_rectangle (&model->polygons[2], -100, 200, 200, 250);
+  polygon_init_rectangle (&model->polygons[3], -200, ground_level,
+			  1200, ground_level + 400);
+
+  polygon_init_rectangle (&model->polygons[4], 300, 320, 400, 350);
+
+
+  model->num_polygons = num_polygons;
+}
+
+static void
 model_init_snake (Model *model)
 {
   const int num_objects = 20;
   const int num_sticks = num_objects * 2 - 3;
   int i;
 
+  memset (model, 0, sizeof *model);
   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->strings = NULL;
-  model->num_strings = 0;
-  model->offsets = NULL;
-  model->num_offsets = 0;
+  model_init_polygons (model);
 
   for (i = 0; i < num_objects; i++) {
     model->objects[i].position.x = random() % 200 + 20;
@@ -126,17 +206,15 @@ model_init_rope (Model *model)
 {
   const int num_objects = 20;
   const int num_sticks = num_objects - 1;
-  const int stick_length = 5;
+  const int stick_length = 10;
   int i;
 
+  memset (model, 0, sizeof *model);
   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->strings = NULL;
-  model->num_strings = 0;
-  model->offsets = NULL;
-  model->num_offsets = 0;
+  model_init_polygons (model);
 
   for (i = 0; i < num_objects; i++) {
     model->objects[i].position.x = 200;
@@ -166,14 +244,14 @@ model_init_curtain (Model *model)
   double x, y;
   int i, j, index, stick_index;
 
+  memset (model, 0, sizeof *model);
   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->strings = NULL;
-  model->num_strings = 0;
   model->offsets = g_new (Offset, num_ropes - 1);
   model->num_offsets = num_ropes - 1;
+  model_init_polygons (model);
 
   for (i = 0; i < num_ropes; i++) {
     for (j = 0; j < num_rope_objects; j++) {
@@ -217,14 +295,14 @@ model_init_grid (Model *model)
   double x, y;
   int i, j, index, string_index;
 
+  memset (model, 0, sizeof *model);
   model->objects = g_new (Object, num_objects);
   model->num_objects = num_objects;
-  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;
+  model_init_polygons (model);
 
   for (i = 0; i < num_ropes; i++) {
     for (j = 0; j < num_rope_objects; j++) {
@@ -267,17 +345,10 @@ static void
 model_fini (Model *model)
 {
   g_free (model->objects);
-  model->objects = NULL;
-  model->num_objects = 0;
   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;
+  memset (model, 0, sizeof *model);
 }
 
 static void
@@ -304,9 +375,9 @@ model_integrate (Model *model, double step)
     y = o->position.y;
     
     o->position.x =
-      x + (x - o->previous_position.x) + o->force.x * step * step;
+      x + 0.9 * (x - o->previous_position.x) + o->force.x * step * step;
     o->position.y =
-      y + (y - o->previous_position.y) + o->force.y * step * step;
+      y + 0.9 * (y - o->previous_position.y) + o->force.y * step * step;
 
     o->previous_position.x = x;
     o->previous_position.y = y;
@@ -336,8 +407,67 @@ estimate_distance (double dx, double dy, double r)
 #endif
 }
 
+static int
+polygon_contains_point (Polygon *polygon, Point *point)
+{
+  int i;
+  double dx, dy;
+
+  for (i = 0; i < polygon->num_points; i++) {
+    dx = point->x - polygon->points[i].x;
+    dy = point->y - polygon->points[i].y;
+
+    if (polygon->normals[i].x * dx + polygon->normals[i].y * dy >= 0)
+      return FALSE;
+  }
+
+  return TRUE;
+}
+
+static void
+polygon_reflect_object (Polygon *polygon, Object *object)
+{
+  int i, edge;
+  double d, distance;
+  Vector *n;
+
+  distance = -1000;
+  for (i = 0; i < polygon->num_points; i++) {
+    d = polygon->normals[i].x * (object->position.x - polygon->points[i].x) +
+      polygon->normals[i].y * (object->position.y - polygon->points[i].y);
+
+    if (d > distance) {
+      distance = d;
+      edge = i;
+      polygon->edge = i;
+      n = &polygon->normals[i];
+    }
+  }
+
+  object->position.x -= (1 + elasticity) * distance * n->x;
+  object->position.y -= (1 + elasticity) * distance * n->y;
+
+  distance =
+    n->x * (object->previous_position.x - polygon->points[edge].x) +
+    n->y * (object->previous_position.y - polygon->points[edge].y);
+
+  object->previous_position.x -= (1 + elasticity) * distance * n->x;
+  object->previous_position.y -= (1 + elasticity) * distance * n->y;
+}
+
 static void
-model_constrain (Model *model, double step)
+model_constrain_polygon (Model *model, Polygon *polygon)
+{
+  int i;
+
+  for (i = 0; i < model->num_objects; i++) {
+    if (polygon_contains_point (polygon, &model->objects[i].position))
+      polygon_reflect_object (polygon, &model->objects[i]);
+  }
+}
+
+static void
+model_constrain (Model *model)
 {
   double dx, dy, x, y, distance, fraction;
   int i;
@@ -350,40 +480,6 @@ model_constrain (Model *model, double step)
     model->anchor_object->previous_position.y = model->anchor_position.y;
   }
 
-  /* FIXME: this should be "is point inside box" test instead. Figure
-   * out from previous_position which edge the point has passed
-   * through and reflect in that. */
-  for (i = 0; i < model->num_objects; i++) {
-    x = model->objects[i].position.x;
-    y = model->objects[i].position.y;
-    if (box_top - edge_fuzz <= y &&
-	model->objects[i].previous_position.y <= box_top + edge_fuzz &&
-	x < box_left) {
-      model->objects[i].position.y = box_top - (y - box_top) * elasticity;
-      model->objects[i].previous_position.y =
-	box_top - (model->objects[i].previous_position.y - box_top) * elasticity;
-    }
-  }
-
-  /* Ground collision detection constraints.  This puts a ground level
-   * in to make sure the points don't fall off the screen. */
-  for (i = 0; i < model->num_objects; i++) {
-    x = model->objects[i].position.x;
-    y = model->objects[i].position.y;
-
-    if (model->objects[i].position.y > ground_level) {
-      model->objects[i].position.y =
-	ground_level - (model->objects[i].position.y - ground_level) * elasticity;
-      model->objects[i].previous_position.y =
-	ground_level - (model->objects[i].previous_position.y - ground_level) * elasticity;
-
-      /* Friction on impact */
-      model->objects[i].position.x =
-	model->objects[i].position.x * (1 - ground_friction) +
-	model->objects[i].previous_position.x * ground_friction;
-    }
-  }
-
   /* Offset constraints. */
   for (i = 0; i < model->num_offsets; i++) {
     x = (model->offsets[i].a->position.x + model->offsets[i].b->position.x) / 2;
@@ -423,6 +519,10 @@ model_constrain (Model *model, double step)
     model->sticks[i].b->position.x = x + dx * (1 - fraction);
     model->sticks[i].b->position.y = y + dy * (1 - fraction);
   }
+
+  /* Polygon constraints. */
+  for (i = 0; i < model->num_polygons; i++)
+    model_constrain_polygon (model, &model->polygons[i]);
 }
 
 static void
@@ -434,7 +534,7 @@ model_step (Model *model, double delta_t)
   model_integrate (model, delta_t);
 
   for (i = 0; i < 100; i++)
-    model_constrain (model, delta_t);
+    model_constrain (model);
 
   model->theta += delta_t;
 }
@@ -549,25 +649,22 @@ draw_offsets (cairo_t *cr,
 }
 
 static void
-draw_constraints (cairo_t *cr,
-		  Model	  *model,
-		  Color   *color)
+draw_polygons (cairo_t *cr, Model *model, Color *color)
 {
-  cairo_set_source_rgba (cr, color->red, color->green, color->blue, 0.5);
-
-  cairo_move_to (cr, 0, ground_level);
-  cairo_line_to (cr, 1500, ground_level);
-  cairo_line_to (cr, 1500, ground_level + 10);
-  cairo_line_to (cr, 0, ground_level + 10);
-  cairo_close_path (cr);
+  Polygon *p;
+  int i, j;
 
-  cairo_move_to (cr, 0, box_top);
-  cairo_line_to (cr, box_left, box_top);
-  cairo_line_to (cr, box_left, box_bottom);
-  cairo_line_to (cr, 0, box_bottom);
-  cairo_close_path (cr);
+  for (i = 0; i < model->num_polygons; i++) {
+    p = &model->polygons[i];
+    cairo_set_source_rgba (cr, color->red, color->green, color->blue, 0.4);
 
+    
+    for (j = 0; j < p->num_points; j++)
+      cairo_line_to (cr, p->points[j].x, p->points[j].y);
+    cairo_close_path (cr);
+  }
   cairo_fill (cr);
+
 }
 
 static void
@@ -608,7 +705,7 @@ expose_event (GtkWidget      *widget,
   cairo_set_source_rgb (cr, 1, 1, 1);
   cairo_paint (cr);
 
-  draw_constraints (cr, closure->model, &red);
+  draw_polygons (cr, closure->model, &blue);
   draw_sticks (cr, closure->model, &black);
   draw_strings (cr, closure->model, &green);
   draw_offsets (cr, closure->model, &blue);
@@ -825,7 +922,6 @@ static gint
 timeout_callback (gpointer data)
 {
   Closure *closure = data;
-  int i;
 
   model_step (closure->model, 1);
 
@@ -877,7 +973,7 @@ main (int argc, char *argv[])
   closure.model = &model;
   closure.frame_count = 0;
   gettimeofday (&closure.start, NULL);
-  g_timeout_add (40, timeout_callback, &closure);
+  g_timeout_add (50, timeout_callback, &closure);
   gtk_main ();
 
   return 0;