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(The "active" function now also exits when the window is closed.)
(The "passive" function now also terminates, when the window is closed; cleaned up the code)
Line 42: Line 42:
 
import Graphics.Rendering.OpenGL (($=))
 
import Graphics.Rendering.OpenGL (($=))
 
import Data.IORef
 
import Data.IORef
  +
import Control.Monad
 
</haskell>
 
</haskell>
   
Line 58: Line 59:
 
GLFW.openWindow (GL.Size 400 400) [GLFW.DisplayAlphaBits 8] GLFW.Window
 
GLFW.openWindow (GL.Size 400 400) [GLFW.DisplayAlphaBits 8] GLFW.Window
 
GLFW.windowTitle $= "GLFW Demo"
 
GLFW.windowTitle $= "GLFW Demo"
GL.shadeModel $= GL.Smooth
+
GL.shadeModel $= GL.Smooth
 
-- enable antialiasing
 
-- enable antialiasing
 
GL.lineSmooth $= GL.Enabled
 
GL.lineSmooth $= GL.Enabled
GL.blend $= GL.Enabled
+
GL.blend $= GL.Enabled
GL.blendFunc $= (GL.SrcAlpha, GL.OneMinusSrcAlpha)
+
GL.blendFunc $= (GL.SrcAlpha, GL.OneMinusSrcAlpha)
GL.lineWidth $= 1.5
+
GL.lineWidth $= 1.5
 
-- set the color to clear background
 
-- set the color to clear background
 
GL.clearColor $= Color4 0 0 0 0
 
GL.clearColor $= Color4 0 0 0 0
  +
 
-- set 2D orthogonal view inside windowSizeCallback because
 
-- set 2D orthogonal view inside windowSizeCallback because
 
-- any change to the Window size should result in different
 
-- any change to the Window size should result in different
 
-- OpenGL Viewport.
 
-- OpenGL Viewport.
GLFW.windowSizeCallback $= (\ size@(GL.Size w h) -> do
+
GLFW.windowSizeCallback $= \ size@(GL.Size w h) ->
GL.viewport $= (GL.Position 0 0, size)
+
do
GL.matrixMode $= GL.Projection
+
GL.viewport $= (GL.Position 0 0, size)
GL.loadIdentity
+
GL.matrixMode $= GL.Projection
GL.ortho2D 0 (realToFrac w) (realToFrac h) 0)
+
GL.loadIdentity
  +
GL.ortho2D 0 (realToFrac w) (realToFrac h) 0
  +
 
-- keep all line strokes as a list of points in an IORef
 
-- keep all line strokes as a list of points in an IORef
 
lines <- newIORef []
 
lines <- newIORef []
Line 89: Line 91:
 
active lines = loop waitForPress
 
active lines = loop waitForPress
 
where
 
where
+
 
loop action = do
 
loop action = do
 
-- draw the entire screen
 
-- draw the entire screen
Line 97: Line 99:
 
-- check whether ESC is pressed for termination
 
-- check whether ESC is pressed for termination
 
p <- GLFW.getKey GLFW.ESC
 
p <- GLFW.getKey GLFW.ESC
case p of
+
unless (p == GLFW.Press) $
GLFW.Press -> return ()
+
do
_ -> do
 
 
-- perform action
 
-- perform action
 
Action action' <- action
 
Action action' <- action
 
-- sleep for 1ms to yield CPU to other applications
 
-- sleep for 1ms to yield CPU to other applications
 
GLFW.sleep 0.001
 
GLFW.sleep 0.001
  +
 
-- only continue when the window is not closed
 
-- only continue when the window is not closed
 
windowOpenStatus <- get $ windowParam Opened
 
windowOpenStatus <- get $ windowParam Opened
if windowOpenStatus == 0
+
unless (windowOpenStatus == 0) $
then return ()
+
loop action' -- loop with next action
else loop action' -- loop with next action
 
   
 
waitForPress = do
 
waitForPress = do
Line 118: Line 121:
 
modifyIORef lines (((x,y):) . ((x,y):))
 
modifyIORef lines (((x,y):) . ((x,y):))
 
return (Action waitForRelease)
 
return (Action waitForRelease)
+
 
waitForRelease = do
 
waitForRelease = do
 
-- keep track of mouse movement while waiting for button
 
-- keep track of mouse movement while waiting for button
Line 143: Line 146:
 
-- disable auto polling in swapBuffers
 
-- disable auto polling in swapBuffers
 
GLFW.disableSpecial GLFW.AutoPollEvent
 
GLFW.disableSpecial GLFW.AutoPollEvent
  +
 
-- keep track of whether ESC has been pressed
 
-- keep track of whether ESC has been pressed
 
quit <- newIORef False
 
quit <- newIORef False
  +
 
-- keep track of whether screen needs to be redrawn
 
-- keep track of whether screen needs to be redrawn
 
dirty <- newIORef True
 
dirty <- newIORef True
  +
 
-- mark screen dirty in refresh callback which is often called
 
-- mark screen dirty in refresh callback which is often called
 
-- when screen or part of screen comes into visibility.
 
-- when screen or part of screen comes into visibility.
GLFW.windowRefreshCallback $= (modifyIORef dirty (\_ -> True))
+
GLFW.windowRefreshCallback $= writeIORef dirty True
  +
 
-- use key callback to track whether ESC is pressed
 
-- use key callback to track whether ESC is pressed
GLFW.keyCallback $= (\k s ->
+
GLFW.keyCallback $= \k s ->
if fromEnum k == fromEnum GLFW.ESC && s == GLFW.Press
+
when (fromEnum k == fromEnum GLFW.ESC && s == GLFW.Press) $
then modifyIORef quit (\_ -> True)
+
writeIORef quit True
else return ())
+
  +
-- Terminate the program if the window is closed
  +
GLFW.windowCloseCallback $= writeIORef quit True
  +
 
-- by default start with waitForPress
 
-- by default start with waitForPress
 
waitForPress dirty
 
waitForPress dirty
 
loop dirty quit
 
loop dirty quit
 
where
 
where
+
 
loop dirty quit = do
 
loop dirty quit = do
 
GLFW.waitEvents
 
GLFW.waitEvents
 
-- redraw screen if dirty
 
-- redraw screen if dirty
 
d <- readIORef dirty
 
d <- readIORef dirty
if d then (render lines >> GLFW.swapBuffers) else return ()
+
modifyIORef dirty (\_ -> False)
+
when d $
  +
render lines >> GLFW.swapBuffers
  +
  +
writeIORef dirty False
 
-- check if we need to quit the loop
 
-- check if we need to quit the loop
 
q <- readIORef quit
 
q <- readIORef quit
if q then return () else loop dirty quit
+
unless q $
  +
loop dirty quit
  +
  +
waitForPress dirty =
  +
do
  +
GLFW.mousePosCallback $= \_ -> return ()
   
waitForPress dirty = do
+
GLFW.mouseButtonCallback $= \b s ->
GLFW.mousePosCallback $= (\_ -> return ())
+
when (b == GLFW.ButtonLeft && s == GLFW.Press) $
GLFW.mouseButtonCallback $= (\b s ->
+
do
if b == GLFW.ButtonLeft && s == GLFW.Press
 
then do
 
 
-- when left mouse button is pressed, add the point
 
-- when left mouse button is pressed, add the point
 
-- to lines and switch to waitForRelease action.
 
-- to lines and switch to waitForRelease action.
Line 178: Line 184:
 
modifyIORef lines (((x,y):) . ((x,y):))
 
modifyIORef lines (((x,y):) . ((x,y):))
 
waitForRelease dirty
 
waitForRelease dirty
else return ())
+
+
waitForRelease dirty =
waitForRelease dirty = do
+
do
GLFW.mousePosCallback $= (\ (Position x y) -> do
+
GLFW.mousePosCallback $= \(Position x y) ->
  +
do
 
-- update the line with new ending position
 
-- update the line with new ending position
 
modifyIORef lines (((x,y):) . tail)
 
modifyIORef lines (((x,y):) . tail)
 
-- mark screen dirty
 
-- mark screen dirty
modifyIORef dirty (\_ -> True))
+
writeIORef dirty True
GLFW.mouseButtonCallback $= (\b s ->
+
  +
GLFW.mouseButtonCallback $= \b s ->
 
-- when left mouse button is released, switch back to
 
-- when left mouse button is released, switch back to
 
-- waitForPress action.
 
-- waitForPress action.
if b == GLFW.ButtonLeft && s == GLFW.Release
+
when (b == GLFW.ButtonLeft && s == GLFW.Release) $
then waitForPress dirty
+
waitForPress dirty
else return ())
 
 
</haskell>
 
</haskell>
   
Line 202: Line 208:
 
GL.clear [GL.ColorBuffer]
 
GL.clear [GL.ColorBuffer]
 
GL.color $ color3 1 0 0
 
GL.color $ color3 1 0 0
GL.renderPrimitive GL.Lines $ foldr (>>) (return ()) (map
+
GL.renderPrimitive GL.Lines $ mapM_
(\ (x, y) -> GL.vertex (vertex3 (fromIntegral x) (fromIntegral y) 0)) l)
+
(\ (x, y) -> GL.vertex (vertex3 (fromIntegral x) (fromIntegral y) 0)) l
  +
   
 
vertex3 :: Float -> Float -> Float -> GL.Vertex3 Float
 
vertex3 :: Float -> Float -> Float -> GL.Vertex3 Float
 
vertex3 = GL.Vertex3
 
vertex3 = GL.Vertex3
  +
   
 
color3 :: Float -> Float -> Float -> GL.Color3 Float
 
color3 :: Float -> Float -> Float -> GL.Color3 Float

Revision as of 20:22, 18 August 2008


Contents

1 About

This is a Haskell module for GLFW OpenGL framework. It provides an alternative to GLUT for OpenGL based Haskell programs.

2 Status

The library is being used by the Haskell School of Expression (SOE) code to render Graphics in a cross-platform manner. It currently interfaces with GLFW version 2.6, works on Windows, Linux (i386) and Mac OS X (both intel and ppc).

GLFW itself is well documented (see GLFW website), and the Haskell module API is documented via Haddock.

Not all functions are fully tested, and there are still a few GLFW C functions missing from the Haskell module, namely the image loading functions. They are excluded because image handling is a separate issue, and low level buffer manipulation would obscure their use further. Texture loading from TGA format is supported both from file and from memory (via a string buffer)..

The Haskell module also provides basic text rendering while GLFW doesn't. It comes from a free 8x16 font which is made into a TGA texture, stored as a Haskell string in the file GLFW.hs. Text rendering is only possible with Alpha enabled. Again, see SOE.hs from the SOE package for sample usage.

GLFW doesn't work well with GHC threads, forkIO or threadDelay. So avoid them if you can.

3 Download

Current version is GLFW-0.3. It's a repackage to work with Cabal 1.2 or later. It now compiles GLFW C source code as part of the building process, please report to the package maintainer if you have build problems.

4 Sample Program

To demonstrate the usage of GLFW for OpenGL based Haskell applications, here is a sample program that allows user to draw lines by holding the left mouse button and move the mouse.

import Graphics.Rendering.OpenGL as GL
import Graphics.UI.GLFW as GLFW
import Graphics.Rendering.OpenGL (($=))
import Data.IORef
import Control.Monad
Because the program needs to process user input, i.e., mouse button and movements, we'll use a continuation like structure for this purpose. The
Action
type represents an IO operation that returns the next
Action
to continue execution.
data Action = Action (IO Action)

The main program is mostly book-keeping such as initializing OpenGL and GLFW, creating window, setting up viewport, etc.

main = do
  GLFW.initialize
  -- open window
  GLFW.openWindow (GL.Size 400 400) [GLFW.DisplayAlphaBits 8] GLFW.Window
  GLFW.windowTitle $= "GLFW Demo"
  GL.shadeModel    $= GL.Smooth
  -- enable antialiasing
  GL.lineSmooth $= GL.Enabled
  GL.blend      $= GL.Enabled
  GL.blendFunc  $= (GL.SrcAlpha, GL.OneMinusSrcAlpha)
  GL.lineWidth  $= 1.5
  -- set the color to clear background
  GL.clearColor $= Color4 0 0 0 0
 
  -- set 2D orthogonal view inside windowSizeCallback because
  -- any change to the Window size should result in different
  -- OpenGL Viewport.
  GLFW.windowSizeCallback $= \ size@(GL.Size w h) ->
    do
      GL.viewport   $= (GL.Position 0 0, size)
      GL.matrixMode $= GL.Projection
      GL.loadIdentity
      GL.ortho2D 0 (realToFrac w) (realToFrac h) 0
 
  -- keep all line strokes as a list of points in an IORef
  lines <- newIORef []
  -- invoke the active drawing loop
  active lines 
  -- finish up
  GLFW.closeWindow
  GLFW.terminate
There are usually two ways to structure the main loop of GLFW programs. One is by actively polling events before processing them. The screen buffer is usually redrawn every time before
swapBuffers
is called. This is the simplest main loop often seen in game applications, and may waste CPU cycles even when there is no visual update. Note that
swapBuffers
by default calls
pollEvents
implicitly, so there is no need to do a separate poll.
-- we start with waitForPress action
active lines = loop waitForPress
  where 
 
    loop action = do
      -- draw the entire screen
      render lines
      -- swap buffer
      GLFW.swapBuffers
      -- check whether ESC is pressed for termination
      p <- GLFW.getKey GLFW.ESC
      unless (p == GLFW.Press) $
        do
            -- perform action
            Action action' <- action
            -- sleep for 1ms to yield CPU to other applications
            GLFW.sleep 0.001
 
            -- only continue when the window is not closed
            windowOpenStatus <- get $ windowParam Opened
            unless (windowOpenStatus == 0) $
              loop action' -- loop with next action
 
    waitForPress = do
      b <- GLFW.getMouseButton GLFW.ButtonLeft
      case b of
        GLFW.Release -> return (Action waitForPress)
        GLFW.Press   -> do
          -- when left mouse button is pressed, add the point
          -- to lines and switch to waitForRelease action.
          (GL.Position x y) <- GL.get GLFW.mousePos 
          modifyIORef lines (((x,y):) . ((x,y):))
          return (Action waitForRelease)
 
    waitForRelease = do
        -- keep track of mouse movement while waiting for button 
        -- release
        (GL.Position x y) <- GL.get GLFW.mousePos
        -- update the line with new ending position
        modifyIORef lines (((x,y):) . tail)
        b <- GLFW.getMouseButton GLFW.ButtonLeft
        case b of
          -- when button is released, switch back back to 
          -- waitForPress action
          GLFW.Release -> return (Action waitForPress)
          GLFW.Press   -> return (Action waitForRelease)
Another way to structure the main loop is to register event callbacks and use
waitEvents
. This way we don't have to put the program to sleep every 1ms because it'll not be using any CPU cycle when there is no event to handle. One reminder in this approach is that
swapBuffers
must be handled with care, because it by default invokes
pollEvents
, which in turn invokes all callback functions. So if
swapBuffers
is used inside a callback, it'll create infinite loop and hang the program. To avoid it, we should disable the
AutoPollEvent
behavior using
disableSpecial
.

Another optimization we can do is to use a dirty marker to remember whether the screen really needs to be redrawn. This'll not only save CPU cycles but also speed up event processing to avoid piling up events in the event queue. Similar tricks can be done to optimize the active polling approach.

passive lines = do
  -- disable auto polling in swapBuffers
  GLFW.disableSpecial GLFW.AutoPollEvent
 
  -- keep track of whether ESC has been pressed
  quit <- newIORef False
 
  -- keep track of whether screen needs to be redrawn
  dirty <- newIORef True
 
  -- mark screen dirty in refresh callback which is often called
  -- when screen or part of screen comes into visibility.
  GLFW.windowRefreshCallback $= writeIORef dirty True
 
  -- use key callback to track whether ESC is pressed
  GLFW.keyCallback $= \k s -> 
     when (fromEnum k == fromEnum GLFW.ESC && s == GLFW.Press) $ 
        writeIORef quit True
 
  -- Terminate the program if the window is closed
  GLFW.windowCloseCallback $= writeIORef quit True
 
  -- by default start with waitForPress
  waitForPress dirty
  loop dirty quit
  where
 
    loop dirty quit = do
        GLFW.waitEvents
        -- redraw screen if dirty
        d <- readIORef dirty
 
        when d $ 
          render lines >> GLFW.swapBuffers
 
        writeIORef dirty False
        -- check if we need to quit the loop
        q <- readIORef quit
        unless q $
          loop dirty quit
 
    waitForPress dirty =
      do
        GLFW.mousePosCallback    $= \_ -> return ()
 
        GLFW.mouseButtonCallback $= \b s -> 
            when (b == GLFW.ButtonLeft && s == GLFW.Press) $
              do
                -- when left mouse button is pressed, add the point
                -- to lines and switch to waitForRelease action.
                (GL.Position x y) <- GL.get GLFW.mousePos
                modifyIORef lines (((x,y):) . ((x,y):))
                waitForRelease dirty
 
    waitForRelease dirty = 
      do 
        GLFW.mousePosCallback $= \(Position x y) ->
          do
            -- update the line with new ending position
            modifyIORef lines (((x,y):) . tail)
            -- mark screen dirty
            writeIORef dirty True
 
        GLFW.mouseButtonCallback $= \b s ->
            -- when left mouse button is released, switch back to
            -- waitForPress action.
            when (b == GLFW.ButtonLeft && s == GLFW.Release) $
              waitForPress dirty
Just replace
active
with
passive
in the
main
function to run the second approach.

The rest of the program goes below.

render lines = do
  l <- readIORef lines
  GL.clear [GL.ColorBuffer]
  GL.color $ color3 1 0 0
  GL.renderPrimitive GL.Lines $ mapM_
      (\ (x, y) -> GL.vertex (vertex3 (fromIntegral x) (fromIntegral y) 0)) l
 
 
vertex3 :: Float -> Float -> Float -> GL.Vertex3 Float
vertex3 = GL.Vertex3
 
 
color3 :: Float -> Float -> Float -> GL.Color3 Float
color3 = GL.Color3