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<pre><a name="line-1"></a><span class='hs-comment'>--------------------------------------------------------------------------------</span>
<a name="line-2"></a><span class='hs-comment'>-- |</span>
<a name="line-3"></a><span class='hs-comment'>-- Module : Graphics.Rendering.OpenGL.GL.StateVar</span>
<a name="line-4"></a><span class='hs-comment'>-- Copyright : (c) Sven Panne 2009</span>
<a name="line-5"></a><span class='hs-comment'>-- License : BSD-style (see the file LICENSE)</span>
<a name="line-6"></a><span class='hs-comment'>-- </span>
<a name="line-7"></a><span class='hs-comment'>-- Maintainer : sven.panne@aedion.de</span>
<a name="line-8"></a><span class='hs-comment'>-- Stability : stable</span>
<a name="line-9"></a><span class='hs-comment'>-- Portability : portable</span>
<a name="line-10"></a><span class='hs-comment'>--</span>
<a name="line-11"></a><span class='hs-comment'>-- State variables are references in the IO monad, like 'IORef's or parts of</span>
<a name="line-12"></a><span class='hs-comment'>-- the OpenGL state. Note that state variables are not neccessarily writable or</span>
<a name="line-13"></a><span class='hs-comment'>-- readable, they may come in read-only or write-only flavours, too. As a very</span>
<a name="line-14"></a><span class='hs-comment'>-- simple example for a state variable, consider an explicitly allocated memory</span>
<a name="line-15"></a><span class='hs-comment'>-- buffer. This buffer can easily be converted into a 'StateVar':</span>
<a name="line-16"></a><span class='hs-comment'>--</span>
<a name="line-17"></a><span class='hs-comment'>-- @</span>
<a name="line-18"></a><span class='hs-comment'>-- makeStateVarFromPtr :: Storable a => Ptr a -> StateVar a</span>
<a name="line-19"></a><span class='hs-comment'>-- makeStateVarFromPtr p = makeStateVar (peek p) (poke p)</span>
<a name="line-20"></a><span class='hs-comment'>-- @</span>
<a name="line-21"></a><span class='hs-comment'>--</span>
<a name="line-22"></a><span class='hs-comment'>-- The example below puts 11 into a state variable (i.e. into the buffer),</span>
<a name="line-23"></a><span class='hs-comment'>-- increments the contents of the state variable by 22, and finally prints the</span>
<a name="line-24"></a><span class='hs-comment'>-- resulting content:</span>
<a name="line-25"></a><span class='hs-comment'>--</span>
<a name="line-26"></a><span class='hs-comment'>-- @</span>
<a name="line-27"></a><span class='hs-comment'>-- do p <- malloc :: IO (Ptr Int)</span>
<a name="line-28"></a><span class='hs-comment'>-- let v = makeStateVarFromPtr p</span>
<a name="line-29"></a><span class='hs-comment'>-- v $= 11</span>
<a name="line-30"></a><span class='hs-comment'>-- v $~ (+ 22)</span>
<a name="line-31"></a><span class='hs-comment'>-- x <- get v</span>
<a name="line-32"></a><span class='hs-comment'>-- print x</span>
<a name="line-33"></a><span class='hs-comment'>-- @</span>
<a name="line-34"></a><span class='hs-comment'>--</span>
<a name="line-35"></a><span class='hs-comment'>-- 'IORef's are state variables, too, so an example with them looks extremely</span>
<a name="line-36"></a><span class='hs-comment'>-- similiar:</span>
<a name="line-37"></a><span class='hs-comment'>--</span>
<a name="line-38"></a><span class='hs-comment'>-- @</span>
<a name="line-39"></a><span class='hs-comment'>-- do v <- newIORef (0 :: Int)</span>
<a name="line-40"></a><span class='hs-comment'>-- v $= 11</span>
<a name="line-41"></a><span class='hs-comment'>-- v $~ (+ 22)</span>
<a name="line-42"></a><span class='hs-comment'>-- x <- get v</span>
<a name="line-43"></a><span class='hs-comment'>-- print x</span>
<a name="line-44"></a><span class='hs-comment'>-- @</span>
<a name="line-45"></a><span class='hs-comment'>--------------------------------------------------------------------------------</span>
<a name="line-46"></a>
<a name="line-47"></a><span class='hs-keyword'>module</span> <span class='hs-conid'>Graphics</span><span class='hs-varop'>.</span><span class='hs-conid'>Rendering</span><span class='hs-varop'>.</span><span class='hs-conid'>OpenGL</span><span class='hs-varop'>.</span><span class='hs-conid'>GL</span><span class='hs-varop'>.</span><span class='hs-conid'>StateVar</span> <span class='hs-layout'>(</span>
<a name="line-48"></a> <span class='hs-comment'>-- * Readable State Variables</span>
<a name="line-49"></a> <span class='hs-conid'>HasGetter</span><span class='hs-layout'>(</span><span class='hs-keyglyph'>..</span><span class='hs-layout'>)</span><span class='hs-layout'>,</span>
<a name="line-50"></a> <span class='hs-conid'>GettableStateVar</span><span class='hs-layout'>,</span> <span class='hs-varid'>makeGettableStateVar</span><span class='hs-layout'>,</span>
<a name="line-51"></a> <span class='hs-comment'>-- * Writable State Variables</span>
<a name="line-52"></a> <span class='hs-conid'>HasSetter</span><span class='hs-layout'>(</span><span class='hs-keyglyph'>..</span><span class='hs-layout'>)</span><span class='hs-layout'>,</span>
<a name="line-53"></a> <span class='hs-conid'>SettableStateVar</span><span class='hs-layout'>,</span> <span class='hs-varid'>makeSettableStateVar</span><span class='hs-layout'>,</span>
<a name="line-54"></a> <span class='hs-comment'>-- * General State Variables</span>
<a name="line-55"></a> <span class='hs-conid'>StateVar</span><span class='hs-layout'>,</span> <span class='hs-varid'>makeStateVar</span><span class='hs-layout'>,</span>
<a name="line-56"></a> <span class='hs-comment'>-- * Utility Functions</span>
<a name="line-57"></a> <span class='hs-layout'>(</span><span class='hs-varop'>$~</span><span class='hs-layout'>)</span><span class='hs-layout'>,</span> <span class='hs-layout'>(</span><span class='hs-varop'>$=!</span><span class='hs-layout'>)</span><span class='hs-layout'>,</span> <span class='hs-layout'>(</span><span class='hs-varop'>$~!</span><span class='hs-layout'>)</span>
<a name="line-58"></a><span class='hs-layout'>)</span> <span class='hs-keyword'>where</span>
<a name="line-59"></a>
<a name="line-60"></a><span class='hs-keyword'>import</span> <span class='hs-conid'>Data</span><span class='hs-varop'>.</span><span class='hs-conid'>IORef</span> <span class='hs-layout'>(</span> <span class='hs-conid'>IORef</span><span class='hs-layout'>,</span> <span class='hs-varid'>readIORef</span><span class='hs-layout'>,</span> <span class='hs-varid'>writeIORef</span> <span class='hs-layout'>)</span>
<a name="line-61"></a>
<a name="line-62"></a><span class='hs-comment'>--------------------------------------------------------------------------------</span>
<a name="line-63"></a>
<a name="line-64"></a><span class='hs-keyword'>infixr</span> <span class='hs-num'>2</span> <span class='hs-varop'>$=</span>
<a name="line-65"></a>
<a name="line-66"></a><span class='hs-comment'>--------------------------------------------------------------------------------</span>
<a name="line-67"></a>
<a name="line-68"></a><a name="HasGetter"></a><span class='hs-comment'>-- | The class of all readable state variables.</span>
<a name="line-69"></a><a name="HasGetter"></a><span class='hs-keyword'>class</span> <span class='hs-conid'>HasGetter</span> <span class='hs-varid'>g</span> <span class='hs-keyword'>where</span>
<a name="line-70"></a> <span class='hs-comment'>-- | Read the value of a state variable.</span>
<a name="line-71"></a> <span class='hs-varid'>get</span> <span class='hs-keyglyph'>::</span> <span class='hs-varid'>g</span> <span class='hs-varid'>a</span> <span class='hs-keyglyph'>-></span> <span class='hs-conid'>IO</span> <span class='hs-varid'>a</span>
<a name="line-72"></a>
<a name="line-73"></a><a name="instance%20HasGetter%20IORef"></a><span class='hs-keyword'>instance</span> <span class='hs-conid'>HasGetter</span> <span class='hs-conid'>IORef</span> <span class='hs-keyword'>where</span>
<a name="line-74"></a> <span class='hs-varid'>get</span> <span class='hs-keyglyph'>=</span> <span class='hs-varid'>readIORef</span>
<a name="line-75"></a>
<a name="line-76"></a><a name="GettableStateVar"></a><span class='hs-comment'>-- | A concrete implementation of a read-only state variable, carrying an IO</span>
<a name="line-77"></a><a name="GettableStateVar"></a><span class='hs-comment'>-- action to read the value.</span>
<a name="line-78"></a><a name="GettableStateVar"></a><span class='hs-keyword'>newtype</span> <span class='hs-conid'>GettableStateVar</span> <span class='hs-varid'>a</span> <span class='hs-keyglyph'>=</span> <span class='hs-conid'>GettableStateVar</span> <span class='hs-layout'>(</span><span class='hs-conid'>IO</span> <span class='hs-varid'>a</span><span class='hs-layout'>)</span>
<a name="line-79"></a>
<a name="line-80"></a><a name="instance%20HasGetter%20GettableStateVar"></a><span class='hs-keyword'>instance</span> <span class='hs-conid'>HasGetter</span> <span class='hs-conid'>GettableStateVar</span> <span class='hs-keyword'>where</span>
<a name="line-81"></a> <span class='hs-varid'>get</span> <span class='hs-layout'>(</span><span class='hs-conid'>GettableStateVar</span> <span class='hs-varid'>g</span><span class='hs-layout'>)</span> <span class='hs-keyglyph'>=</span> <span class='hs-varid'>g</span>
<a name="line-82"></a>
<a name="line-83"></a><a name="makeGettableStateVar"></a><span class='hs-comment'>-- | Construct a 'GettableStateVar' from an IO action.</span>
<a name="line-84"></a><span class='hs-definition'>makeGettableStateVar</span> <span class='hs-keyglyph'>::</span> <span class='hs-conid'>IO</span> <span class='hs-varid'>a</span> <span class='hs-keyglyph'>-></span> <span class='hs-conid'>GettableStateVar</span> <span class='hs-varid'>a</span>
<a name="line-85"></a><span class='hs-definition'>makeGettableStateVar</span> <span class='hs-keyglyph'>=</span> <span class='hs-conid'>GettableStateVar</span>
<a name="line-86"></a>
<a name="line-87"></a><span class='hs-comment'>--------------------------------------------------------------------------------</span>
<a name="line-88"></a>
<a name="line-89"></a><a name="HasSetter"></a><span class='hs-comment'>-- | The class of all writable state variables.</span>
<a name="line-90"></a><a name="HasSetter"></a><span class='hs-keyword'>class</span> <span class='hs-conid'>HasSetter</span> <span class='hs-varid'>s</span> <span class='hs-keyword'>where</span>
<a name="line-91"></a> <span class='hs-comment'>-- | Write a new value into a state variable.</span>
<a name="line-92"></a> <span class='hs-layout'>(</span><span class='hs-varop'>$=</span><span class='hs-layout'>)</span> <span class='hs-keyglyph'>::</span> <span class='hs-varid'>s</span> <span class='hs-varid'>a</span> <span class='hs-keyglyph'>-></span> <span class='hs-varid'>a</span> <span class='hs-keyglyph'>-></span> <span class='hs-conid'>IO</span> <span class='hs-conid'>()</span>
<a name="line-93"></a>
<a name="line-94"></a><a name="instance%20HasSetter%20IORef"></a><span class='hs-keyword'>instance</span> <span class='hs-conid'>HasSetter</span> <span class='hs-conid'>IORef</span> <span class='hs-keyword'>where</span>
<a name="line-95"></a> <span class='hs-layout'>(</span><span class='hs-varop'>$=</span><span class='hs-layout'>)</span> <span class='hs-keyglyph'>=</span> <span class='hs-varid'>writeIORef</span>
<a name="line-96"></a>
<a name="line-97"></a><a name="SettableStateVar"></a><span class='hs-comment'>-- | A concrete implementation of a write-only state variable, carrying an IO</span>
<a name="line-98"></a><a name="SettableStateVar"></a><span class='hs-comment'>-- action to write the new value.</span>
<a name="line-99"></a><a name="SettableStateVar"></a><span class='hs-keyword'>newtype</span> <span class='hs-conid'>SettableStateVar</span> <span class='hs-varid'>a</span> <span class='hs-keyglyph'>=</span> <span class='hs-conid'>SettableStateVar</span> <span class='hs-layout'>(</span><span class='hs-varid'>a</span> <span class='hs-keyglyph'>-></span> <span class='hs-conid'>IO</span> <span class='hs-conid'>()</span><span class='hs-layout'>)</span>
<a name="line-100"></a>
<a name="line-101"></a><a name="instance%20HasSetter%20SettableStateVar"></a><span class='hs-keyword'>instance</span> <span class='hs-conid'>HasSetter</span> <span class='hs-conid'>SettableStateVar</span> <span class='hs-keyword'>where</span>
<a name="line-102"></a> <span class='hs-layout'>(</span><span class='hs-varop'>$=</span><span class='hs-layout'>)</span> <span class='hs-layout'>(</span><span class='hs-conid'>SettableStateVar</span> <span class='hs-varid'>s</span><span class='hs-layout'>)</span> <span class='hs-varid'>a</span> <span class='hs-keyglyph'>=</span> <span class='hs-varid'>s</span> <span class='hs-varid'>a</span>
<a name="line-103"></a>
<a name="line-104"></a><a name="makeSettableStateVar"></a><span class='hs-comment'>-- | Construct a 'SettableStateVar' from an IO action.</span>
<a name="line-105"></a><span class='hs-definition'>makeSettableStateVar</span> <span class='hs-keyglyph'>::</span> <span class='hs-layout'>(</span><span class='hs-varid'>a</span> <span class='hs-keyglyph'>-></span> <span class='hs-conid'>IO</span> <span class='hs-conid'>()</span><span class='hs-layout'>)</span> <span class='hs-keyglyph'>-></span> <span class='hs-conid'>SettableStateVar</span> <span class='hs-varid'>a</span>
<a name="line-106"></a><span class='hs-definition'>makeSettableStateVar</span> <span class='hs-keyglyph'>=</span> <span class='hs-conid'>SettableStateVar</span>
<a name="line-107"></a>
<a name="line-108"></a><span class='hs-comment'>--------------------------------------------------------------------------------</span>
<a name="line-109"></a>
<a name="line-110"></a><a name="StateVar"></a><span class='hs-comment'>-- | A concrete implementation of a readable and writable state variable,</span>
<a name="line-111"></a><a name="StateVar"></a><span class='hs-comment'>-- carrying one IO action to read the value and another IO action to write the</span>
<a name="line-112"></a><a name="StateVar"></a><span class='hs-comment'>-- new value.</span>
<a name="line-113"></a><a name="StateVar"></a><span class='hs-keyword'>data</span> <span class='hs-conid'>StateVar</span> <span class='hs-varid'>a</span> <span class='hs-keyglyph'>=</span>
<a name="line-114"></a> <span class='hs-conid'>StateVar</span> <span class='hs-layout'>(</span><span class='hs-conid'>GettableStateVar</span> <span class='hs-varid'>a</span><span class='hs-layout'>)</span> <span class='hs-layout'>(</span><span class='hs-conid'>SettableStateVar</span> <span class='hs-varid'>a</span><span class='hs-layout'>)</span>
<a name="line-115"></a>
<a name="line-116"></a><a name="instance%20HasGetter%20StateVar"></a><span class='hs-keyword'>instance</span> <span class='hs-conid'>HasGetter</span> <span class='hs-conid'>StateVar</span> <span class='hs-keyword'>where</span>
<a name="line-117"></a> <span class='hs-varid'>get</span> <span class='hs-layout'>(</span><span class='hs-conid'>StateVar</span> <span class='hs-varid'>g</span> <span class='hs-keyword'>_</span><span class='hs-layout'>)</span> <span class='hs-keyglyph'>=</span> <span class='hs-varid'>get</span> <span class='hs-varid'>g</span>
<a name="line-118"></a>
<a name="line-119"></a><a name="instance%20HasSetter%20StateVar"></a><span class='hs-keyword'>instance</span> <span class='hs-conid'>HasSetter</span> <span class='hs-conid'>StateVar</span> <span class='hs-keyword'>where</span>
<a name="line-120"></a> <span class='hs-layout'>(</span><span class='hs-varop'>$=</span><span class='hs-layout'>)</span> <span class='hs-layout'>(</span><span class='hs-conid'>StateVar</span> <span class='hs-keyword'>_</span> <span class='hs-varid'>s</span><span class='hs-layout'>)</span> <span class='hs-varid'>a</span> <span class='hs-keyglyph'>=</span> <span class='hs-varid'>s</span> <span class='hs-varop'>$=</span> <span class='hs-varid'>a</span>
<a name="line-121"></a>
<a name="line-122"></a><a name="makeStateVar"></a><span class='hs-comment'>-- | Construct a 'StateVar' from two IO actions, one for reading and one for</span>
<a name="line-123"></a><span class='hs-comment'>-- writing.</span>
<a name="line-124"></a><span class='hs-definition'>makeStateVar</span> <span class='hs-keyglyph'>::</span> <span class='hs-conid'>IO</span> <span class='hs-varid'>a</span> <span class='hs-keyglyph'>-></span> <span class='hs-layout'>(</span><span class='hs-varid'>a</span> <span class='hs-keyglyph'>-></span> <span class='hs-conid'>IO</span> <span class='hs-conid'>()</span><span class='hs-layout'>)</span> <span class='hs-keyglyph'>-></span> <span class='hs-conid'>StateVar</span> <span class='hs-varid'>a</span>
<a name="line-125"></a><span class='hs-definition'>makeStateVar</span> <span class='hs-varid'>g</span> <span class='hs-varid'>s</span> <span class='hs-keyglyph'>=</span> <span class='hs-conid'>StateVar</span> <span class='hs-layout'>(</span><span class='hs-varid'>makeGettableStateVar</span> <span class='hs-varid'>g</span><span class='hs-layout'>)</span> <span class='hs-layout'>(</span><span class='hs-varid'>makeSettableStateVar</span> <span class='hs-varid'>s</span><span class='hs-layout'>)</span>
<a name="line-126"></a>
<a name="line-127"></a><span class='hs-comment'>--------------------------------------------------------------------------------</span>
<a name="line-128"></a>
<a name="line-129"></a><span class='hs-comment'>-- | A modificator convenience function, transforming the contents of a state</span>
<a name="line-130"></a><span class='hs-comment'>-- variable with a given funtion.</span>
<a name="line-131"></a>
<a name="line-132"></a><a name="$~"></a><span class='hs-layout'>(</span><span class='hs-varop'>$~</span><span class='hs-layout'>)</span> <span class='hs-keyglyph'>::</span> <span class='hs-layout'>(</span><span class='hs-conid'>HasGetter</span> <span class='hs-varid'>v</span><span class='hs-layout'>,</span> <span class='hs-conid'>HasSetter</span> <span class='hs-varid'>v</span><span class='hs-layout'>)</span> <span class='hs-keyglyph'>=></span> <span class='hs-varid'>v</span> <span class='hs-varid'>a</span> <span class='hs-keyglyph'>-></span> <span class='hs-layout'>(</span><span class='hs-varid'>a</span> <span class='hs-keyglyph'>-></span> <span class='hs-varid'>a</span><span class='hs-layout'>)</span> <span class='hs-keyglyph'>-></span> <span class='hs-conid'>IO</span> <span class='hs-conid'>()</span>
<a name="line-133"></a><a name="v"></a><span class='hs-definition'>v</span> <span class='hs-varop'>$~</span> <span class='hs-varid'>f</span> <span class='hs-keyglyph'>=</span> <span class='hs-keyword'>do</span>
<a name="line-134"></a> <span class='hs-varid'>x</span> <span class='hs-keyglyph'><-</span> <span class='hs-varid'>get</span> <span class='hs-varid'>v</span>
<a name="line-135"></a> <span class='hs-varid'>v</span> <span class='hs-varop'>$=</span> <span class='hs-varid'>f</span> <span class='hs-varid'>x</span>
<a name="line-136"></a>
<a name="line-137"></a><a name="$=!"></a><span class='hs-comment'>-- | A variant of '$=' which is strict in the value to be set.</span>
<a name="line-138"></a><span class='hs-layout'>(</span><span class='hs-varop'>$=!</span><span class='hs-layout'>)</span> <span class='hs-keyglyph'>::</span> <span class='hs-conid'>HasSetter</span> <span class='hs-varid'>s</span> <span class='hs-keyglyph'>=></span> <span class='hs-varid'>s</span> <span class='hs-varid'>a</span> <span class='hs-keyglyph'>-></span> <span class='hs-varid'>a</span> <span class='hs-keyglyph'>-></span> <span class='hs-conid'>IO</span> <span class='hs-conid'>()</span>
<a name="line-139"></a><span class='hs-definition'>v</span> <span class='hs-varop'>$=!</span> <span class='hs-varid'>x</span> <span class='hs-keyglyph'>=</span> <span class='hs-varid'>x</span> <span class='hs-varop'>`seq`</span> <span class='hs-varid'>v</span> <span class='hs-varop'>$=</span> <span class='hs-varid'>x</span>
<a name="line-140"></a>
<a name="line-141"></a><a name="$~!"></a><span class='hs-comment'>-- | A variant of '$~' which is strict in the transformed value.</span>
<a name="line-142"></a><span class='hs-layout'>(</span><span class='hs-varop'>$~!</span><span class='hs-layout'>)</span> <span class='hs-keyglyph'>::</span> <span class='hs-layout'>(</span><span class='hs-conid'>HasGetter</span> <span class='hs-varid'>v</span><span class='hs-layout'>,</span> <span class='hs-conid'>HasSetter</span> <span class='hs-varid'>v</span><span class='hs-layout'>)</span> <span class='hs-keyglyph'>=></span> <span class='hs-varid'>v</span> <span class='hs-varid'>a</span> <span class='hs-keyglyph'>-></span> <span class='hs-layout'>(</span><span class='hs-varid'>a</span> <span class='hs-keyglyph'>-></span> <span class='hs-varid'>a</span><span class='hs-layout'>)</span> <span class='hs-keyglyph'>-></span> <span class='hs-conid'>IO</span> <span class='hs-conid'>()</span>
<a name="line-143"></a><span class='hs-definition'>v</span> <span class='hs-varop'>$~!</span> <span class='hs-varid'>f</span> <span class='hs-keyglyph'>=</span> <span class='hs-keyword'>do</span>
<a name="line-144"></a> <span class='hs-varid'>x</span> <span class='hs-keyglyph'><-</span> <span class='hs-varid'>get</span> <span class='hs-varid'>v</span>
<a name="line-145"></a> <span class='hs-varid'>v</span> <span class='hs-varop'>$=!</span> <span class='hs-varid'>f</span> <span class='hs-varid'>x</span>
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