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{-
Feedback.hs (adapted from feedback.c which is (c) Silicon Graphics, Inc.)
Copyright (c) Sven Panne 2002-2005 <sven.panne@aedion.de>
This file is part of HOpenGL and distributed under a BSD-style license
See the file libraries/GLUT/LICENSE
This program demonstrates use of OpenGL feedback. First, a lighting
environment is set up and a few lines are drawn. Then feedback mode is
entered, and the same lines are drawn. The results in the feedback buffer are
printed.
-}
import Control.Monad ( when )
import System.Exit ( exitWith, ExitCode(ExitSuccess) )
import Graphics.UI.GLUT
-- Initialize lighting.
myInit :: IO ()
myInit = do
lighting $= Enabled
light (Light 0) $= Enabled
-- Draw a few lines and two points, one of which will be clipped. If in feedback
-- mode, a passthrough token is issued between each primitive
drawGeometry :: IO ()
drawGeometry = do
mode <- get renderMode
-- resolve overloading, not needed in "real" programs
let normal3f = normal :: Normal3 GLfloat -> IO ()
vertex3f = vertex :: Vertex3 GLfloat -> IO ()
renderPrimitive LineStrip $ do
normal3f (Normal3 0 0 1)
vertex3f (Vertex3 30 30 0)
vertex3f (Vertex3 50 60 0)
vertex3f (Vertex3 70 40 0)
when (mode == Feedback) $
passThrough (PassThroughValue 1)
renderPrimitive Points $
vertex3f (Vertex3 (-100) (-100) (-100)) -- will be clipped
when (mode == Feedback) $
passThrough (PassThroughValue 2)
renderPrimitive Points $ do
normal3f (Normal3 0 0 1)
vertex3f (Vertex3 50 50 0)
flush -- not in original example
printBuffer :: Maybe [FeedbackToken] -> IO ()
printBuffer = maybe (putStrLn "feedback buffer overflow") (mapM_ print)
display :: DisplayCallback
display = do
matrixMode $= Projection
loadIdentity
ortho 0 100 0 100 0 1
clearColor $= Color4 0 0 0 0
clear [ ColorBuffer ]
drawGeometry
(_, tokens) <- getFeedbackTokens 1024 ThreeDColor drawGeometry
printBuffer tokens
keyboard :: KeyboardMouseCallback
keyboard (Char '\27') Down _ _ = exitWith ExitSuccess
keyboard _ _ _ _ = return ()
main :: IO ()
main = do
(progName, _args) <- getArgsAndInitialize
initialDisplayMode $= [ SingleBuffered, RGBMode ]
initialWindowSize $= Size 100 100
initialWindowPosition $= Position 100 100
createWindow progName
myInit
displayCallback $= display
keyboardMouseCallback $= Just keyboard
mainLoop
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