Simulating Physics - Developing Games With Ruby - page 95

def draw_bounding_box
$window . rotate(object . direction, x, y) do
w = @body . width
h = @body . height
$window . draw_quad(
x - w / 2 , y - h / 2 , Gosu :: Color :: RED ,
x + w / 2 , y - h / 2 , Gosu :: Color :: RED ,
x + w / 2 , y + h / 2 , Gosu :: Color :: RED ,
x - w / 2 , y + h / 2 , Gosu :: Color :: RED ,
100 )
end
end
# ...
end
Result is pretty good, we have tank shaped box, so we will be using body image dimensions
to determine our bounding box corners:
Tank's bounding box visualized
There is one problem here though. Gosu::Window#rotate does the rotation math for
us, and we need to perform these calculations on our own. We have four points that we
want to rotate around a center point. It's not very difficult to find how to do this. Here is a
Ruby method for you:
module Utils
# ...
def self . rotate (angle, around_x, around_y, * points)
result = []
points . each_slice( 2 ) do | x, y |
r_x = Math . cos(angle) * (x - around_x) -
Math . sin(angle) * (y - around_y) + around_x
r_y = Math . sin(angle) * (x - around_x) +
Math . cos(angle) * (y - around_y) + around_y