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<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd"><html xmlns="http://www.w3.org/1999/xhtml"><head><meta http-equiv="Content-Type" content="text/html; charset=UTF-8" /><title>Graphics.UI.GLUT.Overlay</title><link href="ocean.css" rel="stylesheet" type="text/css" title="Ocean" /><script src="haddock-util.js" type="text/javascript"></script><script type="text/javascript">//<![CDATA[
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</script></head><body><div id="package-header"><ul class="links" id="page-menu"><li><a href="src/Graphics-UI-GLUT-Overlay.html">Source</a></li><li><a href="index.html">Contents</a></li><li><a href="doc-index.html">Index</a></li></ul><p class="caption">GLUT-2.7.0.1: A binding for the OpenGL Utility Toolkit</p></div><div id="content"><div id="module-header"><table class="info"><tr><th>Copyright</th><td>(c) Sven Panne 2002-2013</td></tr><tr><th>License</th><td>BSD3</td></tr><tr><th>Maintainer</th><td>Sven Panne &lt;svenpanne@gmail.com&gt;</td></tr><tr><th>Stability</th><td>stable</td></tr><tr><th>Portability</th><td>portable</td></tr><tr><th>Safe Haskell</th><td>None</td></tr><tr><th>Language</th><td>Haskell2010</td></tr></table><p class="caption">Graphics.UI.GLUT.Overlay</p></div><div id="table-of-contents"><p class="caption">Contents</p><ul><li><a href="#g:1">Overlay creation and destruction</a></li><li><a href="#g:2">Showing and hiding an overlay</a></li><li><a href="#g:3">Changing the <em>layer in use</em></a></li><li><a href="#g:4">Re-displaying</a></li></ul></div><div id="description"><p class="caption">Description</p><div class="doc"><p>When  overlay hardware is available, GLUT provides a set of routines for
 establishing, using, and removing an overlay for GLUT windows. When an
 overlay is established, a separate OpenGL context is also established. A
 window's overlay OpenGL state is kept distinct from the normal planes'
 OpenGL state.</p></div></div><div id="synopsis"><p id="control.syn" class="caption expander" onclick="toggleSection('syn')">Synopsis</p><ul id="section.syn" class="hide" onclick="toggleSection('syn')"><li class="src short"><a href="#v:hasOverlay">hasOverlay</a> :: <a href="file:///usr/share/doc/libghc-statevar-doc/html/Data-StateVar.html#t:StateVar">StateVar</a> <a href="file:///usr/share/doc/ghc-doc/html/libraries/base-4.8.2.0/Data-Bool.html#t:Bool">Bool</a></li><li class="src short"><a href="#v:overlayPossible">overlayPossible</a> :: <a href="file:///usr/share/doc/libghc-statevar-doc/html/Data-StateVar.html#t:GettableStateVar">GettableStateVar</a> <a href="file:///usr/share/doc/ghc-doc/html/libraries/base-4.8.2.0/Data-Bool.html#t:Bool">Bool</a></li><li class="src short"><a href="#v:overlayVisible">overlayVisible</a> :: <a href="file:///usr/share/doc/libghc-statevar-doc/html/Data-StateVar.html#t:SettableStateVar">SettableStateVar</a> <a href="file:///usr/share/doc/ghc-doc/html/libraries/base-4.8.2.0/Data-Bool.html#t:Bool">Bool</a></li><li class="src short"><span class="keyword">data</span> <a href="#t:Layer">Layer</a><ul class="subs"><li>= <a href="#v:Normal">Normal</a></li><li>| <a href="#v:Overlay">Overlay</a></li></ul></li><li class="src short"><a href="#v:layerInUse">layerInUse</a> :: <a href="file:///usr/share/doc/libghc-statevar-doc/html/Data-StateVar.html#t:StateVar">StateVar</a> <a href="Graphics-UI-GLUT-Overlay.html#t:Layer">Layer</a></li><li class="src short"><a href="#v:postOverlayRedisplay">postOverlayRedisplay</a> :: <a href="file:///usr/share/doc/ghc-doc/html/libraries/transformers-0.4.2.0/Control-Monad-IO-Class.html#t:MonadIO">MonadIO</a> m =&gt; <a href="file:///usr/share/doc/ghc-doc/html/libraries/base-4.8.2.0/Data-Maybe.html#t:Maybe">Maybe</a> <a href="Graphics-UI-GLUT-Window.html#t:Window">Window</a> -&gt; m ()</li></ul></div><div id="interface"><h1 id="g:1">Overlay creation and destruction</h1><div class="top"><p class="src"><a name="v:hasOverlay" class="def">hasOverlay</a> :: <a href="file:///usr/share/doc/libghc-statevar-doc/html/Data-StateVar.html#t:StateVar">StateVar</a> <a href="file:///usr/share/doc/ghc-doc/html/libraries/base-4.8.2.0/Data-Bool.html#t:Bool">Bool</a> <a href="src/Graphics-UI-GLUT-Overlay.html#hasOverlay" class="link">Source</a></p><div class="doc"><p>Controls the overlay for the <em>current window</em>. The requested display mode
 for the overlay is determined by the <em>initial display mode</em>.
 <code><a href="Graphics-UI-GLUT-Overlay.html#v:overlayPossible">overlayPossible</a></code> can be used to determine if an overlay is possible for the
 <em>current window</em> with the current <em>initial display mode</em>. Do not attempt to
 establish an overlay when one is not possible; GLUT will terminate the
 program.</p><p>When <code><a href="Graphics-UI-GLUT-Overlay.html#v:hasOverlay">hasOverlay</a></code> is set to <code><a href="file:///usr/share/doc/ghc-doc/html/libraries/base-4.8.2.0/Data-Bool.html#v:True">True</a></code> when an overlay already exists, the
 existing overlay is first removed, and then a new overlay is established. The
 state of the old overlay's OpenGL context is discarded. Implicitly, the
 window's <em>layer in use</em> changes to the overlay immediately after the overlay
 is established.</p><p>The initial display state of an overlay is shown, however the overlay is only
 actually shown if the overlay's window is shown.</p><p>Setting <code><a href="Graphics-UI-GLUT-Overlay.html#v:hasOverlay">hasOverlay</a></code> to <code><a href="file:///usr/share/doc/ghc-doc/html/libraries/base-4.8.2.0/Data-Bool.html#v:False">False</a></code> is safe even if no overlay is currently
 established, nothing happens in this case. Implicitly, the window's /layer
 in use/ changes to the normal plane immediately once the overlay is removed.</p><p>If the program intends to re-establish the overlay later, it is typically
 faster and less resource intensive to use <code><a href="Graphics-UI-GLUT-Overlay.html#v:overlayVisible">overlayVisible</a></code> to simply change
 the display status of the overlay.</p><p><em>X Implementation Notes:</em> GLUT for X uses the <code>SERVER_OVERLAY_VISUALS</code>
 convention to determine if overlay visuals are available. While the
 convention allows for opaque overlays (no transparency) and overlays with the
 transparency specified as a bitmask, GLUT overlay management only provides
 access to transparent pixel overlays.</p><p>Until RGBA overlays are better understood, GLUT only supports color index
 overlays.</p></div></div><div class="top"><p class="src"><a name="v:overlayPossible" class="def">overlayPossible</a> :: <a href="file:///usr/share/doc/libghc-statevar-doc/html/Data-StateVar.html#t:GettableStateVar">GettableStateVar</a> <a href="file:///usr/share/doc/ghc-doc/html/libraries/base-4.8.2.0/Data-Bool.html#t:Bool">Bool</a> <a href="src/Graphics-UI-GLUT-Overlay.html#overlayPossible" class="link">Source</a></p><div class="doc"><p>Contains <code><a href="file:///usr/share/doc/ghc-doc/html/libraries/base-4.8.2.0/Data-Bool.html#v:True">True</a></code> if an overlay could be established for the <em>current window</em>
 given the current <em>initial display mode</em>. If it contains <code><a href="file:///usr/share/doc/ghc-doc/html/libraries/base-4.8.2.0/Data-Bool.html#v:False">False</a></code>, setting
 <code><a href="Graphics-UI-GLUT-Overlay.html#v:hasOverlay">hasOverlay</a></code> will fail with a fatal error.</p></div></div><h1 id="g:2">Showing and hiding an overlay</h1><div class="top"><p class="src"><a name="v:overlayVisible" class="def">overlayVisible</a> :: <a href="file:///usr/share/doc/libghc-statevar-doc/html/Data-StateVar.html#t:SettableStateVar">SettableStateVar</a> <a href="file:///usr/share/doc/ghc-doc/html/libraries/base-4.8.2.0/Data-Bool.html#t:Bool">Bool</a> <a href="src/Graphics-UI-GLUT-Overlay.html#overlayVisible" class="link">Source</a></p><div class="doc"><p>Controls the visibility of the overlay of the <em>current window</em>.</p><p>The effect of showing or hiding an overlay takes place immediately. Note that
 setting <code><a href="Graphics-UI-GLUT-Overlay.html#v:overlayVisible">overlayVisible</a></code> to <code><a href="file:///usr/share/doc/ghc-doc/html/libraries/base-4.8.2.0/Data-Bool.html#v:True">True</a></code> will not actually display the overlay
 unless the window is also shown (and even a shown window may be obscured by
 other windows, thereby obscuring the overlay). It is typically faster and
 less resource intensive to use the routines below to control the display
 status of an overlay as opposed to removing and re-establishing the overlay.</p></div></div><h1 id="g:3">Changing the <em>layer in use</em></h1><div class="top"><p class="src"><span class="keyword">data</span> <a name="t:Layer" class="def">Layer</a> <a href="src/Graphics-UI-GLUT-Overlay.html#Layer" class="link">Source</a></p><div class="doc"><p>The <em>layer in use</em>.</p></div><div class="subs constructors"><p class="caption">Constructors</p><table><tr><td class="src"><a name="v:Normal" class="def">Normal</a></td><td class="doc"><p>The normal plane.</p></td></tr><tr><td class="src"><a name="v:Overlay" class="def">Overlay</a></td><td class="doc"><p>The overlay.</p></td></tr></table></div><div class="subs instances"><p id="control.i:Layer" class="caption collapser" onclick="toggleSection('i:Layer')">Instances</p><div id="section.i:Layer" class="show"><table><tr><td class="src clearfix"><span class="inst-left"><a href="file:///usr/share/doc/ghc-doc/html/libraries/base-4.8.2.0/Data-Eq.html#t:Eq">Eq</a> <a href="Graphics-UI-GLUT-Overlay.html#t:Layer">Layer</a></span> <a href="src/Graphics-UI-GLUT-Overlay.html#line-119" class="link">Source</a></td><td class="doc empty">&nbsp;</td></tr><tr><td class="src clearfix"><span class="inst-left"><a href="file:///usr/share/doc/ghc-doc/html/libraries/base-4.8.2.0/Data-Ord.html#t:Ord">Ord</a> <a href="Graphics-UI-GLUT-Overlay.html#t:Layer">Layer</a></span> <a href="src/Graphics-UI-GLUT-Overlay.html#line-119" class="link">Source</a></td><td class="doc empty">&nbsp;</td></tr><tr><td class="src clearfix"><span class="inst-left"><a href="file:///usr/share/doc/ghc-doc/html/libraries/base-4.8.2.0/Text-Show.html#t:Show">Show</a> <a href="Graphics-UI-GLUT-Overlay.html#t:Layer">Layer</a></span> <a href="src/Graphics-UI-GLUT-Overlay.html#line-119" class="link">Source</a></td><td class="doc empty">&nbsp;</td></tr></table></div></div></div><div class="top"><p class="src"><a name="v:layerInUse" class="def">layerInUse</a> :: <a href="file:///usr/share/doc/libghc-statevar-doc/html/Data-StateVar.html#t:StateVar">StateVar</a> <a href="Graphics-UI-GLUT-Overlay.html#t:Layer">Layer</a> <a href="src/Graphics-UI-GLUT-Overlay.html#layerInUse" class="link">Source</a></p><div class="doc"><p>Controls the per-window <em>layer in use</em> for the <em>current window</em>, which can
 either be the normal plane or the overlay. Selecting the overlay should only
 be done if an overlay exists, however windows without an overlay may still
 set the <em>layer in use</em> to <code><a href="Graphics-UI-GLUT-Overlay.html#v:Normal">Normal</a></code>. OpenGL commands for the window are
 directed to the current <em>layer in use</em>.</p></div></div><h1 id="g:4">Re-displaying</h1><div class="top"><p class="src"><a name="v:postOverlayRedisplay" class="def">postOverlayRedisplay</a> :: <a href="file:///usr/share/doc/ghc-doc/html/libraries/transformers-0.4.2.0/Control-Monad-IO-Class.html#t:MonadIO">MonadIO</a> m =&gt; <a href="file:///usr/share/doc/ghc-doc/html/libraries/base-4.8.2.0/Data-Maybe.html#t:Maybe">Maybe</a> <a href="Graphics-UI-GLUT-Window.html#t:Window">Window</a> -&gt; m () <a href="src/Graphics-UI-GLUT-Overlay.html#postOverlayRedisplay" class="link">Source</a></p><div class="doc"><p>Mark the overlay of the given window (or the <em>current window</em>, if none is
 supplied) as needing to be redisplayed. The next iteration through
 <code><a href="Graphics-UI-GLUT-Begin.html#v:mainLoop">mainLoop</a></code>, the window's overlay display callback
 (or simply the display callback if no overlay display callback is registered)
 will be called to redisplay the window's overlay plane. Multiple calls to
 <code><a href="Graphics-UI-GLUT-Overlay.html#v:postOverlayRedisplay">postOverlayRedisplay</a></code> before the next display callback opportunity (or
 overlay display callback opportunity if one is registered) generate only a
 single redisplay. <code><a href="Graphics-UI-GLUT-Overlay.html#v:postOverlayRedisplay">postOverlayRedisplay</a></code> may be called within a window's
 display or overlay display callback to re-mark that window for redisplay.</p><p>Logically, overlay damage notification for a window is treated as a
 <code><a href="Graphics-UI-GLUT-Overlay.html#v:postOverlayRedisplay">postOverlayRedisplay</a></code> on the damaged window. Unlike damage reported by the
 window system, <code><a href="Graphics-UI-GLUT-Overlay.html#v:postOverlayRedisplay">postOverlayRedisplay</a></code> will not set to true the overlay's
 damaged status (see <code><a href="Graphics-UI-GLUT-State.html#v:damaged">damaged</a></code>).</p><p>Also, see <code><a href="Graphics-UI-GLUT-Window.html#v:postRedisplay">postRedisplay</a></code>.</p></div></div></div></div><div id="footer"><p>Produced by <a href="http://www.haskell.org/haddock/">Haddock</a> version 2.16.1</p></div></body></html>