Bug 1202 - Add support of Adaptive Vsync via [GLX|WGL]_EXT_swap_control_tear

[GLX|WGL]_EXT_swap_control_tear extensions support
asynchronous buffer swaps, i.e. adaptive Vsync.

<https://www.opengl.org/wiki/SwapInterval_aka_vsync#Adaptive_Vsync>
<https://www.opengl.org/registry/specs/EXT/wgl_swap_control_tear.txt>
<https://www.opengl.org/registry/specs/EXT/glx_swap_control_tear.txt>

<http://keithp.com/blogs/async_flip/>

The extensions utilizes a negative interval value,
enabling late swaps to occur without synchronization to the video frame.

Hence '-1' has new semantics, previously it was the 'default value'
of 'untouched vsync interval'.

New default is:
  - 0 for unrealized context
  - 1 for realized context

+++

It requires [GLX|WGL]_EXT_swap_control,
hence we shall ensure to use use this extension
in the implementation of GLContext.setSwapInterval(..).

+++

Mesa3D seems to support GLX_SGI_swap_control only.

+++

Implemented on Windows and X11.

+++

On GNU/Linux using NVidia driver w/ my setup(*), sadly the query
  GLX.glXQueryDrawable(displayHandle, drawable.getHandle(), GLX.GLX_LATE_SWAPS_TEAR_EXT, val);
always returns zero here, indicating async vsync is not supported.

(Queried the attribute for every frame in windowed or fullscreen mode)

Fullscreen
(*)
  - Debian 8
  - Kernel 3.16
  - KDE/Kwin
  - GL Version     4.5 (Core profile, arb, compat[ES2, ES3, ES31], FBO, hardware) - 4.5.0 NVIDIA 355.06 [GL 4.5.0, vendor 355.6.0 (NVIDIA 355.06)]
  - GL_RENDERER    GeForce GTX 660/PCIe/SSE2
  - Samsung U28D590 (DFP-4): Internal DisplayPort

+++

8 files changed, 208 insertions, 103 deletions

diff --git a/src/jogl/classes/com/jogamp/opengl/GLBase.java b/src/jogl/classes/com/jogamp/opengl/GLBase.java
index dee5f1488..e0c784398 100644
--- a/src/jogl/classes/com/jogamp/opengl/GLBase.java
+++ b/src/jogl/classes/com/jogamp/opengl/GLBase.java
@@ -446,29 +446,43 @@ public interface GLBase {
 
    public boolean isTextureFormatBGRA8888Available();
 
-   /** Provides a platform-independent way to specify the minimum swap
-       interval for buffer swaps. An argument of 0 disables
-       sync-to-vertical-refresh completely, while an argument of 1
-       causes the application to wait until the next vertical refresh
-       until swapping buffers. The default, which is platform-specific,
-       is usually either 0 or 1. This function is not guaranteed to
-       have an effect, and in particular only affects heavyweight
-       onscreen components.
-
-       @see #getSwapInterval
-       @throws GLException if this context is not the current
+   /**
+    * Set the swap interval of the current context and attached <i>onscreen {@link GLDrawable}</i>.
+    * <p>
+    * <i>offscreen {@link GLDrawable}</i> are ignored and {@code false} is returned.
+    * </p>
+    * <p>
+    * The {@code interval} semantics:
+    * <ul>
+    *   <li><i>0</i> disables the vertical synchronization</li>
+    *   <li><i>&ge;1</i> is the number of vertical refreshes before a swap buffer occurs</li>
+    *   <li><i>&lt;0</i> enables <i>late swaps to occur without synchronization to the video frame</i>, a.k.a <i>EXT_swap_control_tear</i>.
+    *              If supported, the absolute value is the minimum number of
+    *              video frames between buffer swaps. If not supported, the absolute value is being used, see above.
+    *   </li>
+    * </ul>
+    * </p>
+    * @param interval see above
+    * @return true if the operation was successful, otherwise false
+    * @throws GLException if the context is not current.
+    * @see GLContext#setSwapInterval(int)
+    * @see #getSwapInterval()
     */
-   public void setSwapInterval(int interval);
-
-   /** Provides a platform-independent way to get the swap
-       interval set by {@link #setSwapInterval}. <br>
+   public void setSwapInterval(int interval) throws GLException;
 
-       If the interval is not set by {@link #setSwapInterval} yet,
-       -1 is returned, indicating that the platforms default
-       is being used.
-
-       @see #setSwapInterval
-     */
+   /**
+    * Return the current swap interval.
+    * <p>
+    * If the context has not been made current at all,
+    * the default value {@code 0} is returned.
+    * </p>
+    * <p>
+    * For a valid context w/ an <o>onscreen {@link GLDrawable}</i> the default value is {@code 1},
+    * otherwise the default value is {@code 0}.
+    * </p>
+    * @see GLContext#getSwapInterval()
+    * @see #setSwapInterval(int)
+    */
    public int getSwapInterval();
 
    /**
@@ -494,12 +508,12 @@ public interface GLBase {
     * for accessing it, including which class or interface contains the
     * functions.
     *
-    * <P>
-    *
+    * <p>
     * Note: it is the intent to add new extensions as quickly as possible
     * to the core GL API. Therefore it is unlikely that most vendors will
     * use this extension mechanism, but it is being provided for
     * completeness.
+    * </p>
     */
    public Object getExtension(String extensionName);
 
diff --git a/src/jogl/classes/com/jogamp/opengl/GLContext.java b/src/jogl/classes/com/jogamp/opengl/GLContext.java
index f68c029df..3ac5df7d4 100644
--- a/src/jogl/classes/com/jogamp/opengl/GLContext.java
+++ b/src/jogl/classes/com/jogamp/opengl/GLContext.java
@@ -237,7 +237,6 @@ public abstract class GLContext {
   protected String ctxVersionString;
   protected VersionNumberString ctxVendorVersion;
   protected VersionNumber ctxGLSLVersion;
-  private int currentSwapInterval;
   protected GLRendererQuirks glRendererQuirks;
 
   /** Did the drawable association changed ? see {@link GLRendererQuirks#NoSetSwapIntervalPostRetarget} */
@@ -258,7 +257,6 @@ public abstract class GLContext {
       ctxGLSLVersion = VersionNumber.zeroVersion;
       attachedObjects.clear();
       contextHandle=0;
-      currentSwapInterval = -1;
       glRendererQuirks = null;
       drawableRetargeted = false;
   }
@@ -1246,50 +1244,41 @@ public abstract class GLContext {
   }
 
   /**
-   * Set the swap interval of the current context and attached drawable.
-   * @param interval Should be &ge; 0. 0 disables the vertical synchronization,
-   *                 where &ge; 1 is the number of vertical refreshes before a swap buffer occurs.
-   *                 A value &lt; 0 is ignored.
+   * Set the swap interval of the current context and attached <i>onscreen {@link GLDrawable}</i>.
+   * <p>
+   * <i>offscreen {@link GLDrawable}</i> are ignored and {@code false} is returned.
+   * </p>
+   * <p>
+   * The {@code interval} semantics:
+   * <ul>
+   *   <li><i>0</i> disables the vertical synchronization</li>
+   *   <li><i>&ge;1</i> is the number of vertical refreshes before a swap buffer occurs</li>
+   *   <li><i>&lt;0</i> enables <i>late swaps to occur without synchronization to the video frame</i>, a.k.a <i>EXT_swap_control_tear</i>.
+   *              If supported, the absolute value is the minimum number of
+   *              video frames between buffer swaps. If not supported, the absolute value is being used, see above.
+   *   </li>
+   * </ul>
+   * </p>
+   * @param interval see above
    * @return true if the operation was successful, otherwise false
-   *
    * @throws GLException if the context is not current.
+   * @see #getSwapInterval()
    */
-  public final boolean setSwapInterval(final int interval) throws GLException {
-    validateCurrent();
-    if(0<=interval) {
-        if( !drawableRetargeted || !hasRendererQuirk(GLRendererQuirks.NoSetSwapIntervalPostRetarget) ) {
-            if( setSwapIntervalImpl(interval) ) {
-                currentSwapInterval = interval;
-                return true;
-            }
-        }
-    }
-    return false;
-  }
-  protected boolean setSwapIntervalImpl(final int interval) {
-      return false;
-  }
-  /** Return the current swap interval.
+  public abstract boolean setSwapInterval(final int interval) throws GLException;
+
+  /**
+   * Return the current swap interval.
    * <p>
    * If the context has not been made current at all,
-   * the default value <code>-1</code> is returned.
+   * the default value {@code 0} is returned.
    * </p>
    * <p>
-   * For a valid context the default value is <code>1</code>
-   * in case of an EGL based profile (ES1 or ES2) and <code>-1</code>
-   * (undefined) for desktop.
+   * For a valid context w/ an <o>onscreen {@link GLDrawable}</i> the default value is {@code 1},
+   * otherwise the default value is {@code 0}.
    * </p>
+   * @see #setSwapInterval(int)
    */
-  public final int getSwapInterval() {
-    return currentSwapInterval;
-  }
-  protected final void setDefaultSwapInterval() {
-    if(this.isGLES()) {
-        currentSwapInterval = 1;
-    } else {
-        currentSwapInterval = -1;
-    }
-  }
+  public abstract int getSwapInterval();
 
   public final boolean queryMaxSwapGroups(final int[] maxGroups, final int maxGroups_offset,
                                           final int[] maxBarriers, final int maxBarriers_offset) {
diff --git a/src/jogl/classes/jogamp/opengl/GLContextImpl.java b/src/jogl/classes/jogamp/opengl/GLContextImpl.java
index fa7aeaff8..39c5796f3 100644
--- a/src/jogl/classes/jogamp/opengl/GLContextImpl.java
+++ b/src/jogl/classes/jogamp/opengl/GLContextImpl.java
@@ -131,6 +131,8 @@ public abstract class GLContextImpl extends GLContext {
   private boolean pixelDataEvaluated;
   private int /* pixelDataInternalFormat, */ pixelDataFormat, pixelDataType;
 
+  private int currentSwapInterval;
+
   protected GL gl;
 
   protected static final Object mappedContextTypeObjectLock;
@@ -209,6 +211,7 @@ public abstract class GLContextImpl extends GLContext {
 
       surfacelessOK = false;
       pixelDataEvaluated = false;
+      currentSwapInterval = 0;
 
       super.resetStates(isInit);
   }
@@ -1110,6 +1113,34 @@ public abstract class GLContextImpl extends GLContext {
     }
   }
 
+  @Override
+  public final boolean setSwapInterval(final int interval) throws GLException {
+    validateCurrent();
+    return setSwapIntervalNC(interval);
+  }
+  protected final boolean setSwapIntervalNC(final int interval) throws GLException {
+    if( drawable.getChosenGLCapabilities().isOnscreen() &&
+        ( !drawableRetargeted || !hasRendererQuirk(GLRendererQuirks.NoSetSwapIntervalPostRetarget) )
+      )
+    {
+        final Integer usedInterval = setSwapIntervalImpl(interval);
+        if( null != usedInterval ) {
+            currentSwapInterval = usedInterval.intValue();
+            return true;
+        }
+    }
+    return false;
+  }
+  protected abstract Integer setSwapIntervalImpl(final int interval);
+
+  public final int getSwapInterval() {
+    return currentSwapInterval;
+  }
+  protected final void setDefaultSwapInterval() {
+    currentSwapInterval = 0;
+    setSwapIntervalNC(1);
+  }
+
   /**
    * Note: Since context creation is temporary, caller need to issue {@link #resetStates(boolean)}, if creation was successful, i.e. returns true.
    * This method does not reset the states, allowing the caller to utilize the state variables.
diff --git a/src/jogl/classes/jogamp/opengl/GLXExtensions.java b/src/jogl/classes/jogamp/opengl/GLXExtensions.java
index 9325c6f68..db4757e4d 100644
--- a/src/jogl/classes/jogamp/opengl/GLXExtensions.java
+++ b/src/jogl/classes/jogamp/opengl/GLXExtensions.java
@@ -34,4 +34,10 @@ public class GLXExtensions {
   public static final String GLX_MESA_swap_control           = "GLX_MESA_swap_control";
   public static final String GLX_SGI_swap_control            = "GLX_SGI_swap_control";
   public static final String GLX_NV_swap_group               = "GLX_NV_swap_group";
+
+  public static final String GLX_EXT_swap_control            = "GLX_EXT_swap_control";
+  public static final String GLX_EXT_swap_control_tear       = "GLX_EXT_swap_control_tear";
+
+  public static final String WGL_EXT_swap_control            = "WGL_EXT_swap_control";
+  public static final String WGL_EXT_swap_control_tear       = "WGL_EXT_swap_control_tear";
 }
diff --git a/src/jogl/classes/jogamp/opengl/egl/EGLContext.java b/src/jogl/classes/jogamp/opengl/egl/EGLContext.java
index b6a05aeeb..b64bb375a 100644
--- a/src/jogl/classes/jogamp/opengl/egl/EGLContext.java
+++ b/src/jogl/classes/jogamp/opengl/egl/EGLContext.java
@@ -51,7 +51,6 @@ import jogamp.opengl.GLContextImpl;
 import jogamp.opengl.GLDrawableImpl;
 import jogamp.opengl.egl.EGLExtImpl;
 import jogamp.opengl.egl.EGLExtProcAddressTable;
-import jogamp.opengl.windows.wgl.WindowsWGLContext;
 
 import com.jogamp.common.ExceptionUtils;
 import com.jogamp.common.nio.Buffers;
@@ -432,11 +431,20 @@ public class EGLContext extends GLContextImpl {
     }
 
     @Override
-    protected boolean setSwapIntervalImpl(final int interval) {
+    protected final Integer setSwapIntervalImpl(final int interval) {
         if( hasRendererQuirk(GLRendererQuirks.NoSetSwapInterval) ) {
-            return false;
+            return null;
         }
-        return EGL.eglSwapInterval(drawable.getNativeSurface().getDisplayHandle(), interval);
+        final int useInterval;
+        if( 0 > interval ) {
+            useInterval = Math.abs(interval);
+        } else {
+            useInterval = interval;
+        }
+        if( EGL.eglSwapInterval(drawable.getNativeSurface().getDisplayHandle(), useInterval) ) {
+            return Integer.valueOf(useInterval);
+        }
+        return null;
     }
 
     static long eglGetProcAddress(final long eglGetProcAddressHandle, final String procname)
diff --git a/src/jogl/classes/jogamp/opengl/macosx/cgl/MacOSXCGLContext.java b/src/jogl/classes/jogamp/opengl/macosx/cgl/MacOSXCGLContext.java
index d4fc0b005..2f88e7619 100644
--- a/src/jogl/classes/jogamp/opengl/macosx/cgl/MacOSXCGLContext.java
+++ b/src/jogl/classes/jogamp/opengl/macosx/cgl/MacOSXCGLContext.java
@@ -423,8 +423,17 @@ public class MacOSXCGLContext extends GLContextImpl
   }
 
   @Override
-  protected boolean setSwapIntervalImpl(final int interval) {
-    return impl.setSwapInterval(interval);
+  protected final Integer setSwapIntervalImpl(final int interval) {
+      final int useInterval;
+      if( 0 > interval ) {
+          useInterval = Math.abs(interval);
+      } else {
+          useInterval = interval;
+      }
+      if( impl.setSwapInterval(useInterval) ) {
+          return Integer.valueOf(useInterval);
+      }
+      return null;
   }
 
   @Override
diff --git a/src/jogl/classes/jogamp/opengl/windows/wgl/WindowsWGLContext.java b/src/jogl/classes/jogamp/opengl/windows/wgl/WindowsWGLContext.java
index a8269ad5c..6ff8c57c8 100644
--- a/src/jogl/classes/jogamp/opengl/windows/wgl/WindowsWGLContext.java
+++ b/src/jogl/classes/jogamp/opengl/windows/wgl/WindowsWGLContext.java
@@ -50,6 +50,7 @@ import com.jogamp.nativewindow.NativeSurface;
 import com.jogamp.opengl.GLContext;
 import com.jogamp.opengl.GLException;
 import com.jogamp.opengl.GLCapabilitiesImmutable;
+import com.jogamp.common.ExceptionUtils;
 import com.jogamp.common.nio.Buffers;
 import com.jogamp.gluegen.runtime.ProcAddressTable;
 import com.jogamp.gluegen.runtime.opengl.GLProcAddressResolver;
@@ -59,6 +60,7 @@ import com.jogamp.opengl.GLRendererQuirks;
 import jogamp.nativewindow.windows.GDI;
 import jogamp.opengl.GLContextImpl;
 import jogamp.opengl.GLDrawableImpl;
+import jogamp.opengl.GLXExtensions;
 
 public class WindowsWGLContext extends GLContextImpl {
   static final Map<String, String> extensionNameMap;
@@ -70,7 +72,8 @@ public class WindowsWGLContext extends GLContextImpl {
   // Table that holds the addresses of the native C-language entry points for
   // WGL extension functions.
   private WGLExtProcAddressTable wglExtProcAddressTable;
-  private int hasSwapIntervalSGI = 0;
+  /** 2 WGL_EXT_swap_control_tear, 1 WGL_EXT_swap_control, 0 undefined, -1 none */
+  private int hasSwapInterval = 0;
   private int hasSwapGroupNV = 0;
 
   static {
@@ -93,7 +96,7 @@ public class WindowsWGLContext extends GLContextImpl {
     wglGLReadDrawableAvailable=false;
     // no inner state _wglExt=null;
     wglExtProcAddressTable=null;
-    hasSwapIntervalSGI = 0;
+    hasSwapInterval = 0;
     hasSwapGroupNV = 0;
     super.resetStates(isInit);
   }
@@ -487,19 +490,39 @@ public class WindowsWGLContext extends GLContextImpl {
   }
 
   @Override
-  protected boolean setSwapIntervalImpl(final int interval) {
-    final WGLExt wglExt = getWGLExt();
-    if(0==hasSwapIntervalSGI) {
+  protected final Integer setSwapIntervalImpl(final int interval) {
+    if( 0 == hasSwapInterval ) {
         try {
-            hasSwapIntervalSGI = wglExt.isExtensionAvailable("WGL_EXT_swap_control")?1:-1;
-        } catch (final Throwable t) { hasSwapIntervalSGI=1; }
+            if ( isExtensionAvailable(GLXExtensions.WGL_EXT_swap_control) ) {
+                hasSwapInterval = 1;
+                if ( isExtensionAvailable(GLXExtensions.WGL_EXT_swap_control_tear) ) {
+                    hasSwapInterval =  2;
+                    if(DEBUG) { System.err.println("WGLContext.setSwapInterval.2 using: "+GLXExtensions.WGL_EXT_swap_control_tear + ", " + GLXExtensions.WGL_EXT_swap_control_tear); }
+                } else {
+                    hasSwapInterval =  1;
+                    if(DEBUG) { System.err.println("WGLContext.setSwapInterval.1 using: "+GLXExtensions.WGL_EXT_swap_control); }
+                }
+            } else {
+                hasSwapInterval = -1;
+                if(DEBUG) { System.err.println("WGLContext.setSwapInterval.0 N/A"); }
+            }
+        } catch (final Throwable t) { hasSwapInterval=-1; if(DEBUG) { ExceptionUtils.dumpThrowable("", t); } }
     }
-    if (hasSwapIntervalSGI>0) {
+    if ( 0 < hasSwapInterval ) { // 2 || 1
+        final int useInterval;
+        if( 1 == hasSwapInterval && 0 > interval ) {
+            useInterval = Math.abs(interval);
+        } else {
+            useInterval = interval;
+        }
         try {
-            return wglExt.wglSwapIntervalEXT(interval);
-        } catch (final Throwable t) { hasSwapIntervalSGI=-1; }
+            final WGLExt wglExt = getWGLExt();
+            if( wglExt.wglSwapIntervalEXT(useInterval) ) {
+                return Integer.valueOf(useInterval);
+            }
+        } catch (final Throwable t) { hasSwapInterval=-1; if(DEBUG) { ExceptionUtils.dumpThrowable("", t); } }
     }
-    return false;
+    return null;
   }
 
   private final int initSwapGroupImpl(final WGLExt wglExt) {
diff --git a/src/jogl/classes/jogamp/opengl/x11/glx/X11GLXContext.java b/src/jogl/classes/jogamp/opengl/x11/glx/X11GLXContext.java
index 63b0b35c0..3f856e4f8 100644
--- a/src/jogl/classes/jogamp/opengl/x11/glx/X11GLXContext.java
+++ b/src/jogl/classes/jogamp/opengl/x11/glx/X11GLXContext.java
@@ -72,7 +72,7 @@ public class X11GLXContext extends GLContextImpl {
   // Table that holds the addresses of the native C-language entry points for
   // GLX extension functions.
   private GLXExtProcAddressTable glXExtProcAddressTable;
-  /** 1 MESA, 2 SGI, 0 undefined, -1 none */
+  /** 3 SGI, 2 GLX_EXT_swap_control_tear, 1 GLX_EXT_swap_control, 0 undefined, -1 none */
   private int hasSwapInterval = 0;
   private int hasSwapGroupNV = 0;
 
@@ -549,39 +549,64 @@ public class X11GLXContext extends GLContextImpl {
   }
 
   @Override
-  protected boolean setSwapIntervalImpl(final int interval) {
-    if( !drawable.getChosenGLCapabilities().isOnscreen() ) { return false; }
-
-    final GLXExt glXExt = getGLXExt();
-    if(0==hasSwapInterval) {
+  protected final Integer setSwapIntervalImpl(final int interval) {
+    final long displayHandle = drawable.getNativeSurface().getDisplayHandle();
+    if( 0 == hasSwapInterval ) {
         try {
-            /** Same impl. ..
-            if( glXExt.isExtensionAvailable(GLXExtensions.GLX_MESA_swap_control) ) {
-                if(DEBUG) { System.err.println("X11GLXContext.setSwapInterval using: "+GLXExtensions.GLX_MESA_swap_control); }
-                hasSwapInterval =  1;
-            } else */
-            if ( glXExt.isExtensionAvailable(GLXExtensions.GLX_SGI_swap_control) ) {
-                if(DEBUG) { System.err.println("X11GLXContext.setSwapInterval using: "+GLXExtensions.GLX_SGI_swap_control); }
-                hasSwapInterval =  2;
+            if ( isExtensionAvailable(GLXExtensions.GLX_EXT_swap_control) ) {
+                hasSwapInterval = 1;
+                if ( isExtensionAvailable(GLXExtensions.GLX_EXT_swap_control_tear) ) {
+                    try {
+                        final IntBuffer val = Buffers.newDirectIntBuffer(1);
+                        GLX.glXQueryDrawable(displayHandle, drawable.getHandle(), GLX.GLX_LATE_SWAPS_TEAR_EXT, val);
+                        if( 1 == val.get(0) ) {
+                            hasSwapInterval =  2;
+                            if(DEBUG) { System.err.println("X11GLXContext.setSwapInterval.2 using: "+GLXExtensions.GLX_EXT_swap_control_tear + ", " + GLXExtensions.GLX_EXT_swap_control_tear); }
+                        } else if(DEBUG) {
+                            System.err.println("X11GLXContext.setSwapInterval.2 n/a: "+GLXExtensions.GLX_EXT_swap_control_tear+", query: "+val.get(0));
+                        }
+                    } catch (final Throwable t) { if(DEBUG) { ExceptionUtils.dumpThrowable("", t); } }
+                }
+                if(DEBUG) {
+                    if( 1 == hasSwapInterval ) {
+                        System.err.println("X11GLXContext.setSwapInterval.1 using: "+GLXExtensions.GLX_EXT_swap_control);
+                    }
+                }
+            } else if ( isExtensionAvailable(GLXExtensions.GLX_SGI_swap_control) ) {
+                hasSwapInterval =  3;
+                if(DEBUG) { System.err.println("X11GLXContext.setSwapInterval.3 using: "+GLXExtensions.GLX_SGI_swap_control); }
             } else {
                 hasSwapInterval = -1;
+                if(DEBUG) { System.err.println("X11GLXContext.setSwapInterval.0 N/A"); }
             }
-        } catch (final Throwable t) { hasSwapInterval=-1; }
+        } catch (final Throwable t) { hasSwapInterval=-1; if(DEBUG) { ExceptionUtils.dumpThrowable("", t); } }
     }
-    /* try {
-        switch( hasSwapInterval ) {
-            case 1:
-                return 0 == glXExt.glXSwapIntervalMESA(interval);
-            case 2:
-                return 0 == glXExt.glXSwapIntervalSGI(interval);
+    if (3 == hasSwapInterval) {
+        final int useInterval;
+        if( 0 > interval ) {
+            useInterval = Math.abs(interval);
+        } else {
+            useInterval = interval;
+        }
+        try {
+            final GLXExt glXExt = getGLXExt();
+            if( 0 == glXExt.glXSwapIntervalSGI(useInterval) ) {
+                return Integer.valueOf(useInterval);
+            }
+        } catch (final Throwable t) { hasSwapInterval=-1; if(DEBUG) { ExceptionUtils.dumpThrowable("", t); } }
+    } else if ( 0 < hasSwapInterval ) { // 2 || 1
+        final int useInterval;
+        if( 1 == hasSwapInterval && 0 > interval ) {
+            useInterval = Math.abs(interval);
+        } else {
+            useInterval = interval;
         }
-    } catch (Throwable t) { hasSwapInterval = -1; } */
-    if (2 == hasSwapInterval) {
         try {
-            return 0 == glXExt.glXSwapIntervalSGI(interval);
-        } catch (final Throwable t) { hasSwapInterval=-1; }
+            GLX.glXSwapIntervalEXT(displayHandle, drawable.getHandle(), useInterval);
+            return Integer.valueOf(useInterval);
+        } catch (final Throwable t) { hasSwapInterval=-1; if(DEBUG) { ExceptionUtils.dumpThrowable("", t); } }
     }
-    return false;
+    return null;
   }
 
   private final int initSwapGroupImpl(final GLXExt glXExt) {