Physics | Collision

bool circleRectCollide(SDL_Point circle, float r,
                       SDL_Rect rect)
{
    // does this assume that circle x and circle y are the center of the circle?
    float closestX = clamp(circle.x, rect.x, rect.x + rect.w);
    float closestY = clamp(circle.y, rect.y, rect.y + rect.h);

    // this gets the distance form the center of the circle to a side of a
    // rectangle. It could be negative or positive. Because we are squaring them
    // it doesn't matter.
    float dx = circle.x - closestX;
    float dy = circle.y - closestY;

    // use the dot product to determine collision
    return (dx*dx + dy*dy) <= (r*r);
}

bool circlesCollide(Circle a, Circle b) {
    float dx = b.x - a.x;
    float dy = b.y - a.y;
    float distance = sqrtf(dx * dx + dy * dy);

    return distance <= (a.r + b.r);
}