From f81a9eff5065f5edda3ca4f1e3e88437c720d431 Mon Sep 17 00:00:00 2001
From: Robert Osfield <robert@openscenegraph.com>
Date: Fri, 1 Oct 2010 18:02:24 +0000
Subject: [PATCH] From Wojciech Lewandowski, "As promised I prepared a patch to
 expose WGL_SWAP_METHOD / PFD_SWAP_METHOD  selection via
 GraphicsContext::Traits. Since Traits don't define any enums (I guess to be
 simple to use) I tried to keep it that way and have added two boolean values:
 swapCopy & swapExchange. It is somewhat similar approach to GDI
 PixelFormatDescription were both options can be present together.  Feel free
 to replace it with enum if you find it more appropriate.

I also uderstand that there is a need to select system wide default  method and have also modified DisplaySettings to contain swapMethod parameter. Swap method in Traits uses value set in DisplaySettings as default. Proper environment and command line args were added.  Its possible to define default DeisplaySettings swap method in standard way via system flags or with comand line.

Env Vars:
    OSG_SWAP_METHOD  = DEFAULT | COPY | EXCHANGE
or Command Line:
    --swap-method   DEFAULT | COPY | EXCHANGE

I also added handling of WM_ERASEBKGND in GraphicsWindowWin32. It may be unneccessary but code should be safer this way than without handling it.  I have placed a comment explaining the reason above the change.

Changes were made against today trunk.

PS. I tested only Windows code. I briefly checked X11 & Cocoa files but have not noticed SwapMethod to be used there.
"
---
 src/osgViewer/GraphicsWindowWin32.cpp | 41 +++++++++++++++++++++++++--
 1 file changed, 39 insertions(+), 2 deletions(-)

diff --git a/src/osgViewer/GraphicsWindowWin32.cpp b/src/osgViewer/GraphicsWindowWin32.cpp
index 160c9fc89..62aba011f 100644
--- a/src/osgViewer/GraphicsWindowWin32.cpp
+++ b/src/osgViewer/GraphicsWindowWin32.cpp
@@ -1474,7 +1474,30 @@ static void PreparePixelFormatSpecifications( const osg::GraphicsContext::Traits
     if (traits.doubleBuffer)
     {
         attributes.enable(WGL_DOUBLE_BUFFER_ARB);
-        if (allowSwapExchangeARB) attributes.set(WGL_SWAP_METHOD_ARB, WGL_SWAP_EXCHANGE_ARB);
+
+        switch ( traits.swapMethod )
+        {
+            case osg::DisplaySettings::SWAP_COPY:
+                attributes.set(WGL_SWAP_METHOD_ARB, WGL_SWAP_COPY_ARB);
+                break;
+            case osg::DisplaySettings::SWAP_EXCHANGE:
+                attributes.set(WGL_SWAP_METHOD_ARB, WGL_SWAP_EXCHANGE_ARB);
+                break;
+            case osg::DisplaySettings::SWAP_UNDEFINED:
+                attributes.set(WGL_SWAP_METHOD_ARB, WGL_SWAP_UNDEFINED_ARB);
+                break;
+            case osg::DisplaySettings::SWAP_DEFAULT:
+                // Wojtek Lewandowski 2010-09-28:
+                // Keep backward compatibility if no method is selected via traits
+                // and let wglSwapExchangeARB flag select swap method. 
+                // However, I would rather remove this flag because its 
+                // now redundant to Traits::swapMethod and it looks like 
+                // WGL_SWAP_EXCHANGE_ARB is the GL default when no WGL_SWAP attrib is given.
+                // To be precise: At least on Windows 7 and Nvidia it seems to be a default.
+                if ( allowSwapExchangeARB )
+                    attributes.set(WGL_SWAP_METHOD_ARB, WGL_SWAP_EXCHANGE_ARB);
+                break;
+        }
     }
 
     if (traits.alpha)         attributes.set(WGL_ALPHA_BITS_ARB,     traits.alpha);
@@ -1503,7 +1526,9 @@ static int ChooseMatchingPixelFormat( HDC hdc, int screenNum, const WGLIntegerAt
             1,                     // version number 
             PFD_DRAW_TO_WINDOW |   // support window 
             PFD_SUPPORT_OPENGL |   // support OpenGL 
-            (_traits->doubleBuffer ? PFD_DOUBLEBUFFER : NULL),      // double buffered ?
+            (_traits->doubleBuffer ? PFD_DOUBLEBUFFER : NULL) |      // double buffered ?            
+            (_traits->swapMethod ==  osg::DisplaySettings::SWAP_COPY ? PFD_SWAP_COPY : NULL) |
+            (_traits->swapMethod ==  osg::DisplaySettings::SWAP_EXCHANGE ? PFD_SWAP_EXCHANGE : NULL),
             PFD_TYPE_RGBA,         // RGBA type 
             _traits->red + _traits->green + _traits->blue,                // color depth
             _traits->red ,0, _traits->green ,0, _traits->blue, 0,          // shift bits ignored 
@@ -2306,6 +2331,18 @@ LRESULT GraphicsWindowWin32::handleNativeWindowingEvent( HWND hwnd, UINT uMsg, W
 
     switch(uMsg)
     {
+        // Wojtek Lewandowski 2010-09-28: 
+        // All web docs on Windows Aero and OpenGL compatibiltiy 
+        // suggest WM_ERASEBKGND should be handled with non NULL value return.
+        // This sugesstion may be irrelevant for our window class 
+        // as default brush pattern is not set so erase flag is forwarded to WM_PAINT 
+        // and gets ignored when WM_PAINT is handled.
+        // But it will certainly be safer and not make things worse 
+        // if we handle this message to be sure everything is done as suggested.
+        case WM_ERASEBKGND :
+            return TRUE;
+            break;
+
         /////////////////
         case WM_PAINT   :
         /////////////////