mirror of
https://github.com/brl/mutter.git
synced 2024-11-28 11:00:54 -05:00
428 lines
9.1 KiB
C
428 lines
9.1 KiB
C
#include "spring-model.h"
|
|
#include <math.h>
|
|
|
|
struct XYPair
|
|
{
|
|
double x, y;
|
|
};
|
|
|
|
#define GRID_WIDTH 4
|
|
#define GRID_HEIGHT 4
|
|
|
|
#define MODEL_MAX_OBJECTS (GRID_WIDTH * GRID_HEIGHT)
|
|
#define MODEL_MAX_SPRINGS (MODEL_MAX_OBJECTS * 2)
|
|
|
|
#define DEFAULT_SPRING_K 5.0
|
|
#define DEFAULT_FRICTION 1.4
|
|
|
|
struct Spring {
|
|
Object *a;
|
|
Object *b;
|
|
/* Spring position at rest, from a to b:
|
|
offset = b.position - a.position
|
|
*/
|
|
Vector offset;
|
|
};
|
|
|
|
struct Object {
|
|
Vector force;
|
|
|
|
Point position;
|
|
Vector velocity;
|
|
|
|
double mass;
|
|
double theta;
|
|
|
|
int immobile;
|
|
};
|
|
|
|
struct Model {
|
|
int num_objects;
|
|
Object objects[MODEL_MAX_OBJECTS];
|
|
|
|
int num_springs;
|
|
Spring springs[MODEL_MAX_SPRINGS];
|
|
|
|
Object *anchor_object;
|
|
Vector anchor_offset;
|
|
|
|
double friction;/* Friction constant */
|
|
double k;/* Spring constant */
|
|
|
|
double last_time;
|
|
double steps;
|
|
};
|
|
|
|
static void
|
|
object_init (Object *object,
|
|
double position_x, double position_y,
|
|
double velocity_x, double velocity_y, double mass)
|
|
{
|
|
object->position.x = position_x;
|
|
object->position.y = position_y;
|
|
|
|
object->velocity.x = velocity_x;
|
|
object->velocity.y = velocity_y;
|
|
|
|
object->mass = mass;
|
|
|
|
object->force.x = 0;
|
|
object->force.y = 0;
|
|
|
|
object->immobile = 0;
|
|
}
|
|
|
|
static void
|
|
spring_init (Spring *spring,
|
|
Object *object_a, Object *object_b,
|
|
double offset_x, double offset_y)
|
|
{
|
|
spring->a = object_a;
|
|
spring->b = object_b;
|
|
spring->offset.x = offset_x;
|
|
spring->offset.y = offset_y;
|
|
}
|
|
|
|
static void
|
|
model_add_spring (Model *model,
|
|
Object *object_a, Object *object_b,
|
|
double offset_x, double offset_y)
|
|
{
|
|
Spring *spring;
|
|
|
|
g_assert (model->num_springs < MODEL_MAX_SPRINGS);
|
|
|
|
spring = &model->springs[model->num_springs];
|
|
model->num_springs++;
|
|
|
|
spring_init (spring, object_a, object_b, offset_x, offset_y);
|
|
}
|
|
|
|
static void
|
|
object_apply_force (Object *object, double fx, double fy)
|
|
{
|
|
object->force.x += fx;
|
|
object->force.y += fy;
|
|
}
|
|
|
|
/* The model here can be understood as a rigid body of the spring's
|
|
* rest shape, centered on the vector between the two object
|
|
* positions. This rigid body is then connected by linear-force
|
|
* springs to each object. This model does degnerate into a simple
|
|
* spring for linear displacements, and does something reasonable for
|
|
* rotation.
|
|
*
|
|
* There are other possibilities for handling the rotation of the
|
|
* spring, and it might be interesting to explore something which has
|
|
* better length-preserving properties. For example, with the current
|
|
* model, an initial 180 degree rotation of the spring results in the
|
|
* spring collapsing down to 0 size before expanding back to it's
|
|
* natural size again.
|
|
*/
|
|
|
|
static void
|
|
spring_exert_forces (Spring *spring, double k)
|
|
{
|
|
Vector da, db;
|
|
Vector a, b;
|
|
|
|
a = spring->a->position;
|
|
b = spring->b->position;
|
|
|
|
/* A nice vector diagram would likely help here, but my ASCII-art
|
|
* skills aren't up to the task. Here's how to make your own
|
|
* diagram:
|
|
*
|
|
* Draw a and b, and the vector AB from a to b
|
|
* Find the center of AB
|
|
* Draw spring->offset so that its center point is on the center of AB
|
|
* Draw da from a to the initial point of spring->offset
|
|
* Draw db from b to the final point of spring->offset
|
|
*
|
|
* The math below should be easy to verify from the diagram.
|
|
*/
|
|
|
|
da.x = 0.5 * (b.x - a.x - spring->offset.x);
|
|
da.y = 0.5 * (b.y - a.y - spring->offset.y);
|
|
|
|
db.x = 0.5 * (a.x - b.x + spring->offset.x);
|
|
db.y = 0.5 * (a.y - b.y + spring->offset.y);
|
|
|
|
object_apply_force (spring->a, k * da.x, k * da.y);
|
|
object_apply_force (spring->b, k * db.x, k * db.y);
|
|
}
|
|
|
|
static void
|
|
model_step_object (Model *model, Object *object)
|
|
{
|
|
Vector acceleration;
|
|
|
|
object->theta += 0.05;
|
|
|
|
/* Slow down due to friction. */
|
|
object->force.x -= model->friction * object->velocity.x;
|
|
object->force.y -= model->friction * object->velocity.y;
|
|
|
|
acceleration.x = object->force.x / object->mass;
|
|
acceleration.y = object->force.y / object->mass;
|
|
|
|
if (object->immobile)
|
|
{
|
|
object->velocity.x = 0;
|
|
object->velocity.y = 0;
|
|
}
|
|
else
|
|
{
|
|
object->velocity.x += acceleration.x;
|
|
object->velocity.y += acceleration.y;
|
|
|
|
object->position.x += object->velocity.x;
|
|
object->position.y += object->velocity.y;
|
|
}
|
|
|
|
object->force.x = 0.0;
|
|
object->force.y = 0.0;
|
|
}
|
|
|
|
static void
|
|
model_init_grid (Model *model, MetaRectangle *rect, gboolean expand)
|
|
{
|
|
int x, y, i, v_x, v_y;
|
|
int hpad, vpad;
|
|
|
|
model->num_objects = MODEL_MAX_OBJECTS;
|
|
|
|
model->num_springs = 0;
|
|
|
|
i = 0;
|
|
if (expand)
|
|
{
|
|
hpad = rect->width / 3;
|
|
vpad = rect->height / 3;
|
|
}
|
|
else
|
|
{
|
|
hpad = rect->width / 6;
|
|
vpad = rect->height / 6;
|
|
}
|
|
|
|
#define EXPAND_DELTA 4
|
|
|
|
for (y = 0; y < GRID_HEIGHT; y++)
|
|
for (x = 0; x < GRID_WIDTH; x++)
|
|
{
|
|
if (expand)
|
|
{
|
|
if (y == 0)
|
|
v_y = - EXPAND_DELTA * g_random_double();
|
|
else if (y == GRID_HEIGHT - 1)
|
|
v_y = EXPAND_DELTA * g_random_double();
|
|
else
|
|
v_y = 2 * EXPAND_DELTA * g_random_double() - EXPAND_DELTA;
|
|
|
|
if (x == 0)
|
|
v_x = - EXPAND_DELTA * g_random_double();
|
|
else if (x == GRID_WIDTH - 1)
|
|
v_x = EXPAND_DELTA * g_random_double();
|
|
else
|
|
v_x = 2 * EXPAND_DELTA * g_random_double() - EXPAND_DELTA;
|
|
}
|
|
else
|
|
{
|
|
v_x = v_y = 0;
|
|
}
|
|
|
|
#if 0
|
|
if (expand)
|
|
object_init (&model->objects[i],
|
|
rect->x + x * rect->width / 6 + rect->width / 4,
|
|
rect->y + y * rect->height / 6 + rect->height / 4,
|
|
v_x, v_y, 20);
|
|
else
|
|
#endif
|
|
{
|
|
#if 0
|
|
g_print ("obj: %d %d\n", rect->x + x * rect->width / 3,
|
|
rect->y + y * rect->height / 3);
|
|
#endif
|
|
object_init (&model->objects[i],
|
|
rect->x + x * rect->width / 3,
|
|
rect->y + y * rect->height / 3,
|
|
v_x, v_y, 15);
|
|
}
|
|
|
|
if (x > 0)
|
|
model_add_spring (model,
|
|
&model->objects[i - 1],
|
|
&model->objects[i],
|
|
hpad, 0);
|
|
|
|
if (y > 0)
|
|
model_add_spring (model,
|
|
&model->objects[i - GRID_WIDTH],
|
|
&model->objects[i],
|
|
0, vpad);
|
|
|
|
i++;
|
|
}
|
|
}
|
|
|
|
static void
|
|
model_init (Model *model, MetaRectangle *rect, gboolean expand)
|
|
{
|
|
model->anchor_object = NULL;
|
|
|
|
model->k = DEFAULT_SPRING_K;
|
|
model->friction = DEFAULT_FRICTION;
|
|
|
|
model_init_grid (model, rect, expand);
|
|
model->steps = 0;
|
|
model->last_time = 0;
|
|
}
|
|
|
|
Model *
|
|
model_new (MetaRectangle *rect, gboolean expand)
|
|
{
|
|
Model *model = g_new0 (Model, 1);
|
|
|
|
model_init (model, rect, expand);
|
|
|
|
return model;
|
|
}
|
|
|
|
static double
|
|
object_distance (Object *object, double x, double y)
|
|
{
|
|
double dx, dy;
|
|
|
|
dx = object->position.x - x;
|
|
dy = object->position.y - y;
|
|
|
|
return sqrt (dx*dx + dy*dy);
|
|
}
|
|
|
|
static Object *
|
|
model_find_nearest (Model *model, double x, double y)
|
|
{
|
|
Object *object = &model->objects[0];
|
|
double distance, min_distance = 0.0;
|
|
int i;
|
|
|
|
for (i = 0; i < model->num_objects; i++) {
|
|
distance = object_distance (&model->objects[i], x, y);
|
|
if (i == 0 || distance < min_distance) {
|
|
min_distance = distance;
|
|
object = &model->objects[i];
|
|
}
|
|
}
|
|
|
|
return object;
|
|
}
|
|
|
|
void
|
|
model_begin_move (Model *model, int x, int y)
|
|
{
|
|
if (model->anchor_object)
|
|
model->anchor_object->immobile = 0;
|
|
|
|
model->anchor_object = model_find_nearest (model, x, y);
|
|
|
|
model->anchor_offset.x = x - model->anchor_object->position.x;
|
|
model->anchor_offset.y = y - model->anchor_object->position.y;
|
|
|
|
g_print ("ypos: %f %f\n", model->anchor_object->position.y,
|
|
model->anchor_object->position.x);
|
|
|
|
g_print ("anchor offset: %f %f\n",
|
|
model->anchor_offset.x,
|
|
model->anchor_offset.y);
|
|
|
|
model->anchor_object->immobile = 1;
|
|
}
|
|
|
|
void
|
|
model_set_anchor (Model *model,
|
|
int x,
|
|
int y)
|
|
{
|
|
if (model->anchor_object)
|
|
model->anchor_object->immobile = 0;
|
|
|
|
model->anchor_object = model_find_nearest (model, x, y);
|
|
model->anchor_offset.x = model->anchor_object->position.x - x;
|
|
model->anchor_offset.y = model->anchor_object->position.y - y;
|
|
|
|
model->anchor_object->immobile = 1;
|
|
}
|
|
|
|
void
|
|
model_update_move (Model *model, int x, int y)
|
|
{
|
|
model->anchor_object->position.x = x - model->anchor_offset.x;
|
|
model->anchor_object->position.y = y - model->anchor_offset.y;
|
|
}
|
|
|
|
static void
|
|
on_end_move (Model *model)
|
|
{
|
|
if (model->anchor_object)
|
|
{
|
|
model->anchor_object->immobile = 0;
|
|
model->anchor_object = NULL;
|
|
}
|
|
}
|
|
|
|
#define EPSILON 0.02
|
|
|
|
gboolean
|
|
model_is_calm (Model *model)
|
|
{
|
|
int i, j;
|
|
gboolean calm = TRUE;
|
|
|
|
for (i = 0; i < model->num_objects; i++)
|
|
{
|
|
if (model->objects[i].velocity.x > EPSILON ||
|
|
model->objects[i].velocity.y > EPSILON ||
|
|
model->objects[i].velocity.x < - EPSILON ||
|
|
model->objects[i].velocity.y < - EPSILON)
|
|
{
|
|
return FALSE;
|
|
}
|
|
}
|
|
|
|
return TRUE;
|
|
}
|
|
|
|
void
|
|
model_step (Model *model)
|
|
{
|
|
int i;
|
|
|
|
for (i = 0; i < model->num_springs; i++)
|
|
spring_exert_forces (&model->springs[i], model->k);
|
|
|
|
for (i = 0; i < model->num_objects; i++)
|
|
model_step_object (model, &model->objects[i]);
|
|
}
|
|
|
|
void
|
|
model_destroy (Model *model)
|
|
{
|
|
g_free (model);
|
|
}
|
|
|
|
void
|
|
model_get_position (Model *model,
|
|
int i,
|
|
int j,
|
|
double *x,
|
|
double *y)
|
|
{
|
|
if (x)
|
|
*x = model->objects[j * 4 + i].position.x;
|
|
|
|
if (y)
|
|
*y = model->objects[j * 4 + i].position.y;
|
|
}
|