{-
Tri3d.hs - Triangles.
For the purpose of efficiency and time, this renderer works with triangles
ONLY.  No quad's, no arbitrary convex polygons, etc. etc. etc.
-}

module Tri3d where

import Vec3d
import Mat3d
import qualified GraphicsUtils as G

type Tri3 a = (Vector3, Vector3, Vector3, a)
type Tri2 a = (Vector2, Vector2, Vector2, a)

rotTriX :: Tri3 a -> Float -> Tri3 a
rotTriX (v1, v2, v3, xtra) theta = (v1', v2', v3', xtra)
    where tm = rotX theta
	  v1' = v1 `vecMultMat` tm
	  v2' = v2 `vecMultMat` tm
	  v3' = v3 `vecMultMat` tm

rotTriY :: Tri3 a -> Float -> Tri3 a
rotTriY (v1, v2, v3, xtra) theta = (v1', v2', v3', xtra)
    where tm = rotY theta
	  v1' = v1 `vecMultMat` tm
	  v2' = v2 `vecMultMat` tm
	  v3' = v3 `vecMultMat` tm

rotTriZ :: Tri3 a -> Float -> Tri3 a
rotTriZ (v1, v2, v3, xtra) theta = (v1', v2', v3', xtra)
    where tm = rotZ theta
	  v1' = v1 `vecMultMat` tm
	  v2' = v2 `vecMultMat` tm
	  v3' = v3 `vecMultMat` tm

{- This is used for the back-to-front sort of the triangle list.
   Very important for rendering properly -}
averageZ :: Tri3 a -> Float
averageZ (v1, v2, v3, _) = (z1 + z2 + z3) / 3.0
    where (_,_,z1) = v1
	  (_,_,z2) = v2
	  (_,_,z3) = v3

flatten :: Tri3 a -> (Vector3 -> Vector2) -> Tri2 a
flatten (v1, v2, v3, xtra) f = (f v1, f v2, f v3, xtra)

zSign :: Tri2 a -> Bool
zSign (v1, v2, v3, _) = (z > 0)
    where (x1,y1) = v1
	  (x2,y2) = v2
	  (x3,y3) = v3
	  z = (x3-x1)*(y3-y2) - (x3-x2)*(y3-y1)