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{-
Histogram.hs (adapted from histogram.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
Compute the histogram of the image. This program illustrates the use of
the histogram function.
-}
import Control.Monad ( zipWithM_ )
import Foreign ( allocaArray, peekArray )
import System.Exit ( exitWith, ExitCode(ExitSuccess) )
import Graphics.UI.GLUT
import ReadImage
histogramSize :: Int
histogramSize = 256 -- Must be a power of 2
myInit :: IO ()
myInit = do
rowAlignment Unpack $= 1
clearColor $= Color4 0 0 0 0
histogram NoProxy $= Just (fromIntegral histogramSize, RGB', PassThrough)
display :: Size -> PixelData a -> DisplayCallback
display size pixels = do
clear [ ColorBuffer ]
-- resolve overloading, not needed in "real" programs
let rasterPos2i = rasterPos :: Vertex2 GLint -> IO ()
rasterPos2i (Vertex2 1 1)
drawPixels size pixels
values <- allocaArray histogramSize $ \buf -> do
-- Note: The example in the Red Book uses GL_UNSIGNED_SHORT here,
-- but we are more honest by using Short...
getHistogram Reset (PixelData RGB Short buf)
peekArray histogramSize buf
-- Plot histogram
zipWithM_ (plotHistogram values)
[ Color3 1 0 0, Color3 0 1 0, Color3 0 0 1 ]
[\(Color3 r _ _) -> r, \(Color3 _ g _) -> g, \(Color3 _ _ b) -> b ]
flush
plotHistogram ::
[Color3 GLshort] -> Color3 GLfloat -> (Color3 GLshort -> GLshort) -> IO ()
plotHistogram values c selectComponent =
renderPrimitive LineStrip $ do
color c
zipWithM_ (\i h -> vertex (Vertex2 i (selectComponent h))) [ 0 .. ] values
reshape :: ReshapeCallback
reshape size = do
viewport $= (Position 0 0, size)
matrixMode $= Projection
loadIdentity
ortho 0 (fromIntegral histogramSize) 0 10000 (-1) 1
matrixMode $= Modelview 0
keyboard :: KeyboardMouseCallback
keyboard (Char 's') Down _ _ = do
Just (width, format, sink) <- get (histogram NoProxy)
let newSink = if sink == Sink then PassThrough else Sink
histogram NoProxy $= Just (width, format, newSink)
postRedisplay Nothing
keyboard (Char '\27') Down _ _ = exitWith ExitSuccess
keyboard _ _ _ _ = return ()
-- Main Loop: Open window with initial window size, title bar, RGBA display
-- mode, and handle input events.
main :: IO ()
main = do
(progName, args) <- getArgsAndInitialize
(size, pixels) <- readImage (if null args then "Data/leeds.bin" else head args)
initialDisplayMode $= [ SingleBuffered, RGBMode ]
initialWindowSize $= size
initialWindowPosition $= Position 100 100
createWindow progName
myInit
reshapeCallback $= Just reshape
keyboardMouseCallback $= Just keyboard
displayCallback $= display size pixels
mainLoop
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