-- | A very simple physics subsytem. It currently detects shape
-- overlaps only, the actual physics movement is carried out
-- in Yampa itself, as it is very simple using integrals and
-- derivatives.
module Physics.TwoDimensions.Physics where

import FRP.Yampa           as Yampa
import Physics.TwoDimensions.Dimensions

data Shape = Rectangle Pos2D Size2D     -- A corner and the whole size
             -- Circle    Pos2D Float   -- Position and radius -- NOT FOR NOW
             -- SemiPlane Pos2D Float   -- Position and angle of plane normal -- NFN

-- | Detects if two shapes overlap.
--
-- Rectangles: overlap if projections on both axis overlap,
-- which happens if x distance between centers is less than the sum
-- of half the widths, and the analogous for y and the heights.

overlapShape :: Shape -> Shape -> Bool
overlapShape (Rectangle p1 s1) (Rectangle p2 s2) = abs dx <= w && abs dy <= h
  where (dx,dy) = (p1 ^+^ (0.5 *^ s1)) ^-^ (p2 ^+^ (0.5 *^ s2))
        (w,h)   = 0.5 *^ (s1 ^+^ s2)