Stashing some 2d collision routines here

2d collision routines.c

// AABB to AABB collision
//  In case of a hit, the first object is pushed out
static int aabb_aabb(short *x, short *y, unsigned short w, unsigned short h,
			   short ox, short oy, unsigned short ow, unsigned short oh)
{
	// find protrusion into each side
	int p_l = *x + w - ox; if (p_l <= 0) return 0;
	int p_r = ox + ow - *x; if (p_r <= 0) return 0;
	int p_u = *y + h - oy; if (p_u <= 0) return 0;
	int p_d = oy + oh - *y; if (p_d <= 0) return 0;

	// collision.  use minimum dist (above) to figure out which edge to lock to
	if (p_l <= p_r && p_l <= p_u && p_l <= p_d)
		*x = ox - w;
	else if (p_r <= p_u && p_r <= p_d)
		*x = ox + ow;
	else if (p_u <= p_d)
		*y = oy - h;
	else
		*y = oy + oh;

	return 1;
}

// Point to Circle collision
//  In case of a hit, the first object is pushed out
static int point_circle(float *x, float *y,
					  float ox, float oy, unsigned short or)
{
	// check distance
	float d_sqr = sqr(ox - *x) + sqr(oy - *y);

	// too close?
	if (d_sqr >= sqr(or)) return 0;

	// determine angle of intrusion
	float theta = atan2f(oy - *y, ox - *x);
	// push first object away
	*x = ox - or * cos(theta);
	*y = oy - or * sin(theta);

	return 1;
}

// Circle to Circle collision
//  In case of a hit, the first object is pushed out
static int circle_circle(float *x, float *y, unsigned short r,
					  float ox, float oy, unsigned short or)
{
	return point_circle(x, y, ox, oy, r + or);
}

// Circle to AABB collision
//  In case of a hit, the first object is pushed out
static int circle_aabb(float *x, float *y, unsigned short r,
						float ox0, float oy0, float ox1, float oy1)
{
	// find protrusion into each side of an expanded square
	float p_l = *x + r - ox0; if (p_l <= 0) return 0;
	float p_r = ox1 + r - *x; if (p_r <= 0) return 0;
	float p_u = *y + r - oy0; if (p_u <= 0) return 0;
	float p_d = oy1 + r - *y; if (p_d <= 0) return 0;

	// it's in the bounding square.
	//  based on the closest edges, test a corner, or don't
	// collision.  use minimum dist (above) to figure out which edge to lock to
	if (p_l <= p_r && p_l <= p_u && p_l <= p_d)
	{
		// left edge
		if (*y < oy0) return point_circle(x, y, ox0, oy0, r); 
		else if (*y > oy1) return point_circle(x, y, ox0, oy1, r); 
		else *x = ox0 - r;
	} else if (p_r <= p_u && p_r <= p_d) {
		// right edge
		if (*y < oy0) return point_circle(x, y, ox1, oy0, r); 
		else if (*y > oy1) return point_circle(x, y, ox1, oy1, r); 
		else *x = ox1 + r;
	} else if (p_u <= p_d) {
		// top edge
		if (*x < ox0) return point_circle(x, y, ox0, oy0, r); 
		else if (*x > ox1) return point_circle(x, y, ox1, oy0, r); 
		else *y = oy0 - r;
	} else {
		// bottom edge
		// top edge
		if (*x < ox0) return point_circle(x, y, ox0, oy1, r); 
		else if (*x > ox1) return point_circle(x, y, ox1, oy1, r); 
		else *y = oy1 + r;
	}

	return 1;
}

// Ray to AABB collision
//  Return a distance at which the collision happens (or t_start if never)
static float ray_aabb(float x0, float y0, float dx, float dy,
						float ox0, float oy0, float ox1, float oy1)
{
    float tmin = -FLT_MAX; float tmax = FLT_MAX;

//	float ray_dx = x1 - x0;
	if (dx != 0.0) {
        double tx1 = (ox0 - x0)/dx;
        double tx2 = (ox1 - x0)/dx;

        tmin = max(tmin, min(tx1, tx2));
        tmax = min(tmax, max(tx1, tx2));
    }

//	float ray_dy = y1 - y0;
    if (dy != 0.0) {
        double ty1 = (oy0 - y0)/dy;
        double ty2 = (oy1 - y0)/dy;

        tmin = max(tmin, min(ty1, ty2));
        tmax = min(tmax, max(ty1, ty2));
    }

	if (tmax >= tmin) return tmin;
	else return FLT_MAX;
}

// Ray to Circle collision
//  Return a distance at which the collision happens (or t_start if never)
static float ray_circle(float x0, float y0, float dx, float dy,
						float ox, float oy, float or)
{
	// determine the 
    float tmin = -FLT_MAX; float tmax = FLT_MAX;

//	float ray_dx = x1 - x0;
	if (dx != 0.0) {
        double tx1 = (ox0 - x0)/dx;
        double tx2 = (ox1 - x0)/dx;

        tmin = max(tmin, min(tx1, tx2));
        tmax = min(tmax, max(tx1, tx2));
    }

//	float ray_dy = y1 - y0;
    if (dy != 0.0) {
        double ty1 = (oy0 - y0)/dy;
        double ty2 = (oy1 - y0)/dy;

        tmin = max(tmin, min(ty1, ty2));
        tmax = min(tmax, max(ty1, ty2));
    }

	if (tmax >= tmin) return tmin;
	else return FLT_MAX;
}