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{-
BlendEqn.hs (adapted from blendeqn.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
Demonstrate the different blending functions available with the OpenGL
imaging subset. This program demonstrates use of blendEquation.
The following keys change the selected blend equation function:
'a' -> FuncAdd
's' -> FuncSubtract
'r' -> FuncReverseSubtract
'm' -> Min
'x' -> Max
-}
import Data.Char ( toLower )
import System.Exit ( exitWith, ExitCode(ExitSuccess) )
import Graphics.UI.GLUT
myInit :: IO ()
myInit = do
clearColor $= Color4 1 1 0 0
blendFunc $= (One, One)
blend $= Enabled
display :: DisplayCallback
display = do
clear [ ColorBuffer ]
color (Color3 0 0 (1 :: GLfloat))
rect (Vertex2 (-0.5) (-0.5)) (Vertex2 0.5 (0.5 :: GLfloat))
flush
reshape :: ReshapeCallback
reshape size@(Size w h) = do
let aspect = fromIntegral w / fromIntegral h
viewport $= (Position 0 0, size)
matrixMode $= Projection
loadIdentity
if aspect < 1
then let aspect' = recip aspect
in ortho (-aspect') aspect' (-1) 1 (-1) 1
else ortho (-1) 1 (-aspect) aspect (-1) 1
matrixMode $= Modelview 0
keyboard :: KeyboardMouseCallback
keyboard (Char c) Down _ _ = case toLower c of
-- Colors are added as: (0, 0, 1) + (1, 1, 0) = (1, 1, 1)
-- which will produce a white square on a yellow background.
'a' -> setBlendEquation FuncAdd
-- Colors are subtracted as: (0, 0, 1) - (1, 1, 0) = (-1, -1, 1)
-- which is clamped to (0, 0, 1), producing a blue square on a
-- yellow background
's' -> setBlendEquation FuncSubtract
-- Colors are subtracted as: (1, 1, 0) - (0, 0, 1) = (1, 1, -1)
-- which is clamed to (1, 1, 0). This produces yellow for both
-- the square and the background.
'r' -> setBlendEquation FuncReverseSubtract
-- The minimum of each component is computed, as
-- [min(0, 1), min(0, 1), min(1, 0)] which equates to (0, 0, 0).
-- This will produce a black square on the yellow background.
'm' -> setBlendEquation Min
-- The minimum of each component is computed, as
-- [max(0, 1), max(0, 1), max(1, 0)] which equates to (1, 1, 1)
-- This will produce a white square on the yellow background.
'x' -> setBlendEquation Max
'\27' -> exitWith ExitSuccess
_ -> return ()
where setBlendEquation e = do
blendEquation $= e
postRedisplay Nothing
keyboard _ _ _ _ = return ()
main :: IO ()
main = do
(progName, _args) <- getArgsAndInitialize
initialDisplayMode $= [ SingleBuffered, RGBMode ]
initialWindowSize $= Size 512 512
initialWindowPosition $= Position 100 100
createWindow progName
myInit
reshapeCallback $= Just reshape
keyboardMouseCallback $= Just keyboard
displayCallback $= display
mainLoop
|
