-- graphics
display state = do
drawState =<< get state
simTime <- simulate =<< get state
sleep (max 0 $ frameTime - simTime)
drawState :: State -> IO ()
drawState st = do
pos <- get $ ballPos st
G. clear [G.ColorBuffer]
drawWalls
drawBall pos
G. swapBuffers
drawBall :: H.Position -> IO ()
298 | Глава 20: Императивное программирование
drawBall pos = do
G. color red
circle x y $ d2gl ballRadius
where (x, y) = vec2gl pos
drawWalls :: IO ()
drawWalls = do
G. color black
line (-dow2) (-doh2) (-dow2) doh2
line (-dow2) doh2
dow2
doh2
line dow2
doh2
dow2
(-doh2)
line dow2
(-doh2)
(-dow2) (-doh2)
where dow2 = d2gl ow2
doh2 = d2gl oh2
onMouse state = do
mb <- G. getMouseButton ButtonLeft
when (mb == Press) (get G. mousePos >>= updateVel state)
updateVel state pos = do
size <- get G. windowSize
st <- get state
p0 <- get $ ballPos st
v0 <- get $ ballVel st
let p1 = mouse2canvas size pos
ballVel st $=
H. scale (H. normalize $ p1 - p0) (max minVel $ H. len v0)
mouse2canvas :: G.Size -> G.Position -> H.Vector
mouse2canvas (G.Size sx sy) (G.Position mx my) = H.Vector x y
where d a b
= fromIntegral a / fromIntegral b