flying-balls/balls.c

#include <stdlib.h>
#include <math.h>
#include <assert.h>

#include "game.h"
#include "balls.h"
#include "gravity.h"

unsigned int radius_min = 5;
unsigned int radius_max = 10;

unsigned int v_max = 100;
unsigned int v_min = 0;

unsigned int v_angle_min = 0;
unsigned int v_angle_max = 100;

struct ball * balls = 0;
unsigned int n_balls = 50;

static void random_velocity(struct ball * p) {
    double r2;
    do {
	p->v_x = v_min + rand() % (v_max + 1 - v_min);
	p->v_y = v_min + rand() % (v_max + 1 - v_min);
	r2 = p->v_x*p->v_x + p->v_y*p->v_y;
    } while (r2 > v_max*v_max || r2 < v_min*v_min);
}

void balls_init_state () {
    static const unsigned int border = 10;
    unsigned int w = width < 2*border ? 1 : width - 2*border;
    unsigned int h = height < 2*border ? 1 : height - 2*border;

    for (unsigned int i = 0; i < n_balls; ++i) {
	balls[i].x = border + rand() % w;
	balls[i].y = border + rand() % h;
	random_velocity(balls + i);
	if (rand() % 2)
	    balls[i].v_x = -balls[i].v_x;
	if (rand() % 2)
	    balls[i].v_y = -balls[i].v_y;
	balls[i].radius = radius_min + rand() % (radius_max + 1 - radius_min);
	unsigned int v_angle_360 = (v_angle_min + rand() % (v_angle_max + 1 - v_angle_min)) % 360;
	balls[i].v_angle = 2*M_PI*v_angle_360/360;
	balls[i].angle = (rand() % 360)*2*M_PI/360;
    }
}

void ball_update_state (struct ball * p) {
    struct gravity_vector g;
    gravity_get_vector (&g, p);

    p->x += delta*p->v_x + delta*delta*g.x/2.0;
    p->v_x += delta*g.x;

    p->y += delta*p->v_y + delta*delta*g.y/2.0;
    p->v_y += delta*g.y;

    if (p->x + p->radius > width) { /* right wall */
	if (p->v_x > 0) {
	    p->x -= p->x + p->radius - width;
	    p->v_x = -p->v_x;
	}
    } else if (p->x < p->radius) { /* left wall */
	if (p->v_x < 0) {
	    p->x += p->radius - p->x;
	    p->v_x = -p->v_x;
	}
    } 

    if (p->y + p->radius > height) { /* bottom wall */
	if (p->v_y > 0) {
	    p->y -= p->y + p->radius - height;
	    p->v_y = -p->v_y;
	}
    } else if (p->y < p->radius) { /* top wall */
	if (p->v_y < 0) {
	    p->y += p->radius - p->y;
	    p->v_y = -p->v_y;
	}
    } 
    p->angle += delta*p->v_angle;
    while (p->angle >= 2*M_PI)
	p->angle -= 2*M_PI;
    while (p->angle < 0)
	p->angle += 2*M_PI;
}

void ball_elastic_collision (struct ball * p, struct ball * q) {
    double dx = q->x - p->x;
    double dy = q->y - p->y;
    double d2 = dx*dx + dy*dy;
    double r = p->radius + q->radius;
    if (d2 <= r*r) {
	double dv_x = q->v_x - p->v_x;
	double dv_y = q->v_y - p->v_y;

	double mp = p->radius * p->radius;
	double mq = q->radius * q->radius;

	double f = dv_x*dx + dv_y*dy;

	if (f < 0) {
	    f /= d2*(mp + mq);
	    p->v_x += 2*mq*f*dx;
	    p->v_y += 2*mq*f*dy;

	    q->v_x -= 2*mp*f*dx;
	    q->v_y -= 2*mp*f*dy;
	}
    }
}

void ball_reposition (struct ball * b) {
    if (b->x < b->radius)
	b->x = b->radius;
    else if (b->x + b->radius > width)
	b->x = width - b->radius;
    if (b->y < b->radius)
	b->y = b->radius;
    else if (b->y + b->radius > height)
	b->y = height - b->radius;
}

const char * face_filename = 0;
int face_rotation = 0;

static const double linear_rotation_unit = 2.0;

static unsigned int faces_count;
static struct ball_face ** faces;

struct ball_face {
    unsigned int rotations;
    cairo_surface_t ** c_faces;
};

static double random_color_component() {
    return 1.0*(rand() % 200 + 56)/255;
};

static struct ball_face * new_ball_face(unsigned int radius, cairo_surface_t * face, int rotation) {
    struct ball_face * f = malloc(sizeof(struct ball_face));
    if (!f)
	return 0;
    if (face && rotation) {
	f->rotations = 2*M_PI * radius / linear_rotation_unit;
    } else {
	f->rotations = 1;
    }
    f->c_faces = malloc(sizeof(cairo_surface_t *)*f->rotations);
    if (!f->c_faces) {
	free(f);
	return 0;
    }
    for (int i = 0; i < f->rotations; ++i) {
	f->c_faces[i] = gdk_window_create_similar_surface(gtk_widget_get_window(canvas),
							  CAIRO_CONTENT_COLOR_ALPHA,
							  2*radius, 2*radius);
	assert(f->c_faces[i]);
	cairo_t * ball_cr = cairo_create(f->c_faces[i]);
	cairo_translate(ball_cr, radius, radius);
	cairo_arc(ball_cr, 0.0, 0.0, radius, 0, 2 * M_PI);
	cairo_clip(ball_cr);

	if (face) {
	    int face_x_offset = cairo_image_surface_get_width (face) / 2;
	    int face_y_offset = cairo_image_surface_get_height (face) / 2;
	    cairo_rotate(ball_cr, i*2*M_PI/f->rotations);
	    cairo_scale (ball_cr, 1.0 * radius / face_x_offset, 1.0 * radius / face_y_offset);
	    cairo_set_source_surface(ball_cr, face, -face_x_offset, -face_y_offset);
	    cairo_paint(ball_cr);
	} else {
	    cairo_pattern_t *pat;
	    pat = cairo_pattern_create_radial (-0.2*radius, -0.2*radius, 0.2*radius,
					       -0.2*radius, -0.2*radius, 1.3*radius);
	    double col_r = random_color_component();
	    double col_g = random_color_component();
	    double col_b = random_color_component();
	    cairo_pattern_add_color_stop_rgba (pat, 0, col_r, col_g, col_b, 1);
	    cairo_pattern_add_color_stop_rgba (pat, 1, col_r/3, col_g/3, col_b/3, 1);
	    cairo_set_source (ball_cr, pat);
	    cairo_arc (ball_cr, 0.0, 0.0, radius, 0, 2 * M_PI);
	    cairo_fill (ball_cr);
	}
	cairo_surface_flush(f->c_faces[i]);
	cairo_destroy(ball_cr);
    }
    return f;
}

static void balls_init_faces () {
    cairo_surface_t * face_surface = 0;

    if (face_filename) {
	face_surface = cairo_image_surface_create_from_png (face_filename);
	if (cairo_surface_status(face_surface) != CAIRO_STATUS_SUCCESS) {
	    cairo_surface_destroy (face_surface);
	    face_surface = 0;
	    fprintf(stderr, "could not create surface from PNG file %s\n", face_filename);
	}
    }
    if (face_surface) {
	faces_count = radius_max + 1 - radius_min;
	faces = malloc(sizeof(struct ball_face *)*faces_count);
	for (unsigned int i = 0; i < faces_count; ++i)
	    faces[i] = 0;
	for(struct ball * b = balls; b != balls + n_balls; ++b) {
	    unsigned int r_idx = b->radius - radius_min;
	    if (!faces[r_idx])
		faces[r_idx] = new_ball_face(b->radius, face_surface, face_rotation);
	    b->face = faces[r_idx];
	}
	cairo_surface_destroy (face_surface);
    } else {
	faces_count = n_balls;
	faces = malloc(sizeof(struct ball_face *)*faces_count);
	for (unsigned int i = 0; i < n_balls; ++i)
	    balls[i].face = faces[i] = new_ball_face(balls[i].radius, 0, face_rotation);
    }
}

void balls_draw (cairo_t * cr) {
    for (const struct ball * b = balls; b != balls + n_balls; ++b) {
	cairo_save(cr);
	cairo_translate(cr, b->x - b->radius, b->y - b->radius);
	unsigned int face_id;
	if (b->face->rotations == 1)
	    face_id = 0;
	else {
	    face_id = b->face->rotations*b->angle/(2*M_PI);
	    assert(face_id < b->face->rotations);
	    if (face_id >= b->face->rotations)
		face_id %= b->face->rotations;
	}
	cairo_set_source_surface(cr, b->face->c_faces[face_id], 0, 0);
	cairo_paint(cr);
	cairo_restore(cr);
    }
}

static void balls_destroy_faces () {
    if (!faces)
	return;
    for (int i = 0; i < faces_count; ++i) {
	if (faces[i]) {
	    if (faces[i]->c_faces) {
		for (unsigned int j = 0; j < faces[i]->rotations; ++j)
		    cairo_surface_destroy(faces[i]->c_faces[j]);
		free(faces[i]->c_faces);
	    }
	    free(faces[i]);
	}
    }
    free (faces);
    faces = 0;
    faces_count = 0;
}

void balls_destroy () {
    balls_destroy_faces ();
    free (balls);
}

void balls_init () {
    balls = malloc(sizeof(struct ball)*n_balls);
    assert(balls);
    balls_init_state ();
    balls_init_faces ();
}