Seamless Integration of an FBObject based GLFBODrawable as GLOffscreenAutoDrawable.FBO and as an OffscreenLayerSurface's drawable (OSX) - Fix Bugs 569 and 599

Summary:
=========
The new FBObject based GLFBODrawable implementation allows the seamless utilization of
FBO offscreen rendering in single buffer, double buffer and MSAA mode.

The GLFBODrawable uses a parent drawable based on a
dummy surface to allow a GLOffscreenAutoDrawable.FBO creation
or a mutable surface supporting an existing offscreen layer surface (OSX CALayer).

Offscreen GLDrawable's and GLOffscreenAutoDrawable's can be selected via the
GLCapabilities. If simply !onscreen is selected in the caps instance w/o enabling FBO, PBuffer or Bitmap,
the factory will automatically choose regarding availability:
   FBO > PBuffer > Bitmap

Double buffering is supported in MSAA more (intrinsic) and explicit in non MSAA.
It is preferred when delivering resources (texture id's or framebuffer names)
to a shared GLContext.
This is demonstrated in (emulates our OSX CALayer implementation):
  TestFBOOffThreadSharedContextMix2DemosES2NEWT,
  TestFBOOnThreadSharedContext1DemoES2NEWT
and with the OSX JAWT OffscreenLayerSurface itself. FBO is the preferred choice.

+++

Offscreen drawables can be resized while maintaining a bound GLContext (e.g. w/ GLAutoDrawable).
Previously both, drawable and context, needed to be destroyed and recreated at offscreen resize.
Common implementation in GLDrawableHelper is used in the implementations
(NEWT's GLWindow, AWT GLCanvas, SWT GLCanvas).

+++

Tested:
=======

Manually run all unit tests on:
  - Linux x86_64 NVidia/AMD/Mesa3d(ES)
  - OSX x86_64 NVidia
  - Windows x86_64 NVidia
  - Android arm Mali-400/Tegra-2

No regressions.

Disclaimer:
===========
This feature is committed almost in one patch.

Both previous commits were introducing / fixing the capabilities behavior:
 90d45928186f2be99999461cfe45f76a783cc961
 9036376b7806a5fc61590bf49404eb71830de92f

I have to appologize for the huge size and impact (files and platforms) of this commit
however, I could not find a better way to inject this feature in one sane piece.

NativeWindow Details:
=====================

Complete decoupling of platform impl. detail of surfaces
implementing ProxySurface. Used to generalize dummy surfaces and EGL surfaces
on top of a native platform surface.
  - ProxySurface.UpstreamSurfaceHook -> UpstreamSurfaceHook
  - abstract class ProxySurface -> interface ProxySurface + ProxySurfaceImpl
  - Misc. implementations

JOGL Details:
=====================

FBOObject: API Change / Simplification & Usability
  - Removed reference counter to remove complexity, allow user to choose.
  - Add 'dispose' flag for detachColorbuffer(..), allowing to keep attachment alive
  - Fix equals operation of Attachment
  - Check pre-exising GL errors
  - Interface Colobuffer gets lifecycle methods
  - Add static factory methods to create Attachments w/o FBObject instance
  - Reset:
    - Clip min size to 1
    - Keep alive samplingSink, i.e. don't issue resetMSAATexture2DSink(..).
      It gets called at syncFramebuffer()/use(..) later on before actual usage.
      This allows the consumer to utilize the GL_FRONT buffer until (e.g.) swap.
  - misc bugfixes

GLOffscreenAutoDrawable: API Change
  - Reloc and interfacing
  - class com.jogamp.opengl.OffscreenAutoDrawable -> javax.media.opengl.*
    interfaces GLOffscreenAutoDrawable extends GLAutoDrawable
               GLOffscreenAutoDrawable.FBO extends GLOffscreenAutoDrawable, GLFBODrawable
  - Added general implementation and FBO specialization
  - Replacing GLPBuffer (deprecated) .. usable for any offscreen GLDrawable via factory

GLAutoDrawable:
  - Add 'GLDrawable getDelegatedDrawable()'
  - Refine documentation of setContext(..), remove disclaimer and fixme tags

GLDrawableFactory:
  - Refine API doc and it's selection mechanism for offscreen.
  - Add createOffscreenDrawable(..)
  - Add createOffscreenAutoDrawable(..)
  - Add canCreateFBO(..)
  - Mark createGLPbuffer(..) deprectated

Mark GLPBuffer deprecated

New: GLFBODrawable extends GLDrawable

GLCanvas (AWT and SWT): Add offscreen resize support w/o GLContext recreation

GLAutoDrawableBase .. GLWindow:
  - Add offscreen resize support w/o GLContext recreation
  - Remove double swapBuffer call
  -

GLBase/GLContext:
  - Add:
    - boolean hasBasicFBOSupport()
    - boolean hasFullFBOSupport()
    - int getMaxRenderbufferSamples()
    - boolean isTextureFormatBGRA8888Available()

GLContext: Fix version detection and hasGLSL()
  - Version detection in setGLFunctionAvailability(..)
    - Query GL_VERSION ASAP and parse it and compare w/ given major/minor
    - Use parsed version if valid and lower than given _or_ given is invalid.
    - Use validated version for caching (procaddr, ..), version number, etc.

  - Fix hasGLSL()
    Since 'isGL2ES2()' is true if 'isGL2()'
    and the latter simply alows GL 1.*, we confine the result to a GL >= 2.0
    on desktops. FIXME: May consider GL 1.5 w/ extensions.
    -  return isGL2ES2();
    +      return isGLES2() ||
    +             isGL3() ||
    +             isGL2() && ctxMajorVersion>1 ;

GLDrawableImpl:
  - Add 'associateContext(GLContext, boolean)' allowing impl.
    to have a (weak) reference list of bound context.
    This is was pulled up from the OSX specific drawable impl.
  - swapBuffersImpl() -> swapBuffersImpl(boolean doubleBuffered)
    and call it regardless of single buffering.
    This is required to propagate this event to impl. properly,
    i.e. FBODrawable requires a swap notification.
  - Clarify 'contextMadeCurrent(..)' protocol

GLDrawableHelper:
  - Add resize and recreate offscreen drawable util method
  - Simplify required init/reshape calls for GLEventListener
  -

GLGraphicsConfigurationUtil:
  - fixWinAttribBitsAndHwAccel: Reflect sharede context hw-accel bits
  - OSX has no offscreen bitmap, use pbuffer
  - use proper offscreen auto selection if offscreen and no modes are set

EGL Context/Drawable/DrawableFactory: Abstract native platform code out of base classes
  - Use EGLWrappedSurface w/ UpstreamSurfaceHook to handle upstream (X11, WGL, ..)
    lifecycle - in case the EGL resource is hooked up on it.

Invisible dummy surfaces: All platforms
  - size is now reduced to 64x64 and decoupled of actual generic mutable size
  - fix device  lifecycle, no more leaks

+++

OSX
====

Enable support for GLFBODrawableImpl in offscreen CALayer mode
  - NSOpenGLImpl: hooks to calayer native code
  - calayer code:
    - allows pbuffer and texures (FBO)
    - decouple size and draw calls avoiding flickering
    - enable auto resize of calayer tree

MacOSXCGLContext:
  - NSOpenGLImpl:
  - Fix false pbuffer 'usage', validate the pointer
  - If !pbuffer, copy other window mode bits of caps
  -

MacOSXCGLGraphicsConfiguration:
  - Only assume pbuffer if !onscreen
  - Remove reference of native pixelformat pointer

Native code:
  - use 'respondsToSelector:' query before calling 'new' methods
    avoiding an error message where unsuported (prev. OSX versions)
  - if monitor refresh-rate is queried 0, set to default 60hz
  - add missing NSAutoreleasePool decoration

+++

Android / NEWT:
===============

Issue setVisible(..) w/o wait, i.e. queue on EDT,
@Android surfaceChanged() callback. Otherwise we could deadlock:
   setVisible(..) -> EDT -> setVisibleImpl(..) -> 'GL-display'.
the latter may may cause havoc while Android-EDT is blocked [until it's return].

1 files changed, 415 insertions, 81 deletions

diff --git a/src/jogl/classes/jogamp/opengl/GLFBODrawableImpl.java b/src/jogl/classes/jogamp/opengl/GLFBODrawableImpl.java
index 03bc26cbc..de45466f3 100644
--- a/src/jogl/classes/jogamp/opengl/GLFBODrawableImpl.java
+++ b/src/jogl/classes/jogamp/opengl/GLFBODrawableImpl.java
@@ -1,142 +1,476 @@
 package jogamp.opengl;
 
 import javax.media.nativewindow.NativeSurface;
+import javax.media.nativewindow.NativeWindowException;
+import javax.media.nativewindow.ProxySurface;
+import javax.media.nativewindow.UpstreamSurfaceHook;
 import javax.media.opengl.GL;
-import javax.media.opengl.GL2GL3;
+import javax.media.opengl.GLCapabilities;
 import javax.media.opengl.GLCapabilitiesImmutable;
 import javax.media.opengl.GLContext;
 import javax.media.opengl.GLException;
+import javax.media.opengl.GLFBODrawable;
 
 import com.jogamp.nativewindow.MutableGraphicsConfiguration;
 import com.jogamp.opengl.FBObject;
 import com.jogamp.opengl.FBObject.Attachment;
+import com.jogamp.opengl.FBObject.Colorbuffer;
 import com.jogamp.opengl.FBObject.TextureAttachment;
 
 /**
- * Offscreen GLDrawable implementation using framebuffer object (FBO)
- * as it's offscreen rendering mechanism.
+ * {@link FBObject} offscreen GLDrawable implementation, i.e. {@link GLFBODrawable}.
+ * <p>
+ * It utilizes the context lifecycle hook {@link #contextRealized(GLContext, boolean)}
+ * to initialize the {@link FBObject} instance.
+ * </p>
+ * <p>
+ * It utilizes the context current hook {@link #contextMadeCurrent(GLContext, boolean) contextMadeCurrent(context, true)} 
+ * to {@link FBObject#bind(GL) bind} the FBO.
+ * </p>
+ * See {@link GLFBODrawable} for double buffering details.
  * 
  * @see GLDrawableImpl#contextRealized(GLContext, boolean)
  * @see GLDrawableImpl#contextMadeCurrent(GLContext, boolean)
  * @see GLDrawableImpl#getDefaultDrawFramebuffer()
  * @see GLDrawableImpl#getDefaultReadFramebuffer()
  */
-public class GLFBODrawableImpl extends GLDrawableImpl {
-    final GLDrawableImpl parent;
-    final FBObject fbo;
-    int texUnit;
-    int samplesTexUnit = 0;
-    int width=0, height=0, samples=0;
-    
-    protected GLFBODrawableImpl(GLDrawableFactoryImpl factory, GLDrawableImpl parent, 
-                                NativeSurface surface, int initialWidth, int initialHeight, int textureUnit) {
+public class GLFBODrawableImpl extends GLDrawableImpl implements GLFBODrawable {
+    protected static final boolean DEBUG = GLDrawableImpl.DEBUG || Debug.debug("FBObject");
+    
+    private final GLDrawableImpl parent;
+    
+    private boolean initialized;
+    private int texUnit;
+    private int samples;
+    
+    private FBObject[] fbos;
+    private int fboIBack;  // points to GL_BACK buffer
+    private int fboIFront; // points to GL_FRONT buffer
+    private FBObject pendingFBOReset = null;
+    private boolean fboBound;
+    private static final int bufferCount = 2; // number of FBOs for double buffering. TODO: Possible to configure!
+    
+    // private DoubleBufferMode doubleBufferMode; // TODO: Add or remove TEXTURE (only) DoubleBufferMode support
+    
+    private SwapBufferContext swapBufferContext;
+    
+    public static interface SwapBufferContext {
+        public void swapBuffers(boolean doubleBuffered);
+    }
+    
+    protected GLFBODrawableImpl(GLDrawableFactoryImpl factory, GLDrawableImpl parent, NativeSurface surface, 
+                                GLCapabilitiesImmutable fboCaps, int textureUnit) {
         super(factory, surface, false);
+        this.initialized = false;
+
+        // Replace the chosen caps of dummy-surface w/ it's clone and copied values of orig FBO caps request.
+        // The dummy-surface has already been configured, hence value replace is OK
+        // and due to cloning, the native GLCapability portion is being preserved. 
+        final MutableGraphicsConfiguration msConfig = (MutableGraphicsConfiguration) surface.getGraphicsConfiguration();
+        final GLCapabilities fboCapsNative = (GLCapabilities) msConfig.getChosenCapabilities().cloneMutable();
+        fboCapsNative.copyFrom(fboCaps);
+        msConfig.setChosenCapabilities(fboCapsNative);
+            
         this.parent = parent;
         this.texUnit = textureUnit;
-        final GLCapabilitiesImmutable caps = (GLCapabilitiesImmutable) surface.getGraphicsConfiguration().getChosenCapabilities();
-        this.width = initialWidth;
-        this.height = initialHeight;
-        this.samples = caps.getNumSamples();
-        this.fbo = new FBObject();
+        this.samples = fboCaps.getNumSamples();
+        
+        // default .. // TODO: Add or remove TEXTURE (only) DoubleBufferMode support
+        // this.doubleBufferMode = ( samples > 0 || fboCaps.getDoubleBuffered() ) ? DoubleBufferMode.FBO : DoubleBufferMode.NONE ;
+        
+        this.swapBufferContext = null;
     }
     
-    @Override
-    protected void contextRealized(GLContext glc, boolean realized) {
-        final GLCapabilitiesImmutable caps = (GLCapabilitiesImmutable) surface.getGraphicsConfiguration().getChosenCapabilities();
-        final GL gl = glc.getGL();
-        if(realized) {                   
-            fbo.reset(gl, width, height, samples);
-            samples = fbo.getNumSamples(); // update, maybe capped
+    private final void initialize(boolean realize, GL gl) {        
+        if(realize) {
+            final int maxSamples = gl.getMaxRenderbufferSamples();
+            samples = samples <= maxSamples ? samples : maxSamples;
+            
+            final GLCapabilitiesImmutable caps = (GLCapabilitiesImmutable) surface.getGraphicsConfiguration().getChosenCapabilities();
+            final int fbosN;
             if(samples > 0) {
-                fbo.attachColorbuffer(gl, 0, caps.getAlphaBits()>0);
+                fbosN = 1;
+            } else if( caps.getDoubleBuffered() ) {
+                fbosN = bufferCount;
             } else {
-                fbo.attachTexture2D(gl, 0, caps.getAlphaBits()>0);
+                fbosN = 1;
             }
-            if( caps.getStencilBits() > 0 ) {
-                fbo.attachRenderbuffer(gl, Attachment.Type.DEPTH_STENCIL, 24);
-            } else {
-                fbo.attachRenderbuffer(gl, Attachment.Type.DEPTH, 24);
+
+            fbos = new FBObject[fbosN];
+            fboIBack = 0;                // head
+            fboIFront = fbos.length - 1; // tail
+            
+            for(int i=0; i<fbosN; i++) {
+                fbos[i] = new FBObject();
+                fbos[i].reset(gl, getWidth(), getHeight(), samples);
+                if(fbos[i].getNumSamples() != samples) {
+                    throw new InternalError("Sample number mismatch: "+samples+", fbos["+i+"] "+fbos[i]);
+                }
+                if(samples > 0) {
+                    fbos[i].attachColorbuffer(gl, 0, caps.getAlphaBits()>0);
+                } else {
+                    fbos[i].attachTexture2D(gl, 0, caps.getAlphaBits()>0);
+                }
+                if( caps.getStencilBits() > 0 ) {
+                    fbos[i].attachRenderbuffer(gl, Attachment.Type.DEPTH_STENCIL, 24);
+                } else {
+                    fbos[i].attachRenderbuffer(gl, Attachment.Type.DEPTH, 24);
+                }
             }
-        } else if(null != fbo) {
-            fbo.destroy(gl);
-        }
-    }
-    
-    @Override
-    protected void contextMadeCurrent(GLContext glc, boolean current) {
-        final GL gl = glc.getGL();
-        if(current) {
-            fbo.bind(gl);
+            fbos[fboIFront].syncFramebuffer(gl);
+            fboBound = false;
+            final GLCapabilities fboCapsNative = (GLCapabilities) surface.getGraphicsConfiguration().getChosenCapabilities();
+            fbos[0].formatToGLCapabilities(fboCapsNative);
+            fboCapsNative.setDoubleBuffered( fboCapsNative.getDoubleBuffered() || samples > 0 );
+            
+            initialized = true;            
         } else {
-            fbo.unbind(gl);
-            final TextureAttachment attachment = samples > 0 ? fbo.getSamplingSink() : (TextureAttachment) fbo.getColorbuffer(0) ;
-            if(null == attachment) {
-                throw new GLException("Null texture colorbuffer, samples "+samples+", "+fbo.toString());
-            }
-            gl.glActiveTexture(GL.GL_TEXTURE0 + texUnit);
-            fbo.use(gl, attachment );
-            if( samples > 0) {
-                gl.glBindFramebuffer(GL2GL3.GL_READ_FRAMEBUFFER, fbo.getReadFramebuffer());
+            initialized = false;
+            
+            for(int i=0; i<fbos.length; i++) {
+                fbos[i].destroy(gl);
             }
+            fbos=null;
+            fboBound = false;   
+            pendingFBOReset = null;
+        }
+        if(DEBUG) {
+            System.err.println("GLFBODrawableImpl.initialize("+realize+"): "+this);
+            Thread.dumpStack();
         }
     }
     
-    @Override
-    protected int getDefaultDrawFramebuffer() { return fbo.getWriteFramebuffer(); }
-    
-    @Override
-    protected int getDefaultReadFramebuffer() { return fbo.getReadFramebuffer(); }
-    
-    public FBObject getFBObject() { return fbo; }
-    
-    public void setSize(GL gl, int newWidth, int newHeight) throws GLException {
-        width = newWidth;
-        height = newHeight;        
-        fbo.reset(gl, width, height, samples);
-        samples = fbo.getNumSamples(); // update, maybe capped
+    public final void setSwapBufferContext(SwapBufferContext sbc) {
+        swapBufferContext = sbc;
+    }
+
+    private static final void reset(GL gl, FBObject fbo, int fboIdx, int width, int height, int samples) {
+        fbo.reset(gl, width, height, samples); // implicit glClear(..)
+        if(fbo.getNumSamples() != samples) {
+            throw new InternalError("Sample number mismatch: "+samples+", fbos["+fboIdx+"] "+fbo);
+        }        
     }
     
-    public void setSamples(GL gl, int newSamples) throws GLException {
-        samples = newSamples;
-        fbo.reset(gl, width, height, samples);
-        samples = fbo.getNumSamples(); // update, maybe capped
+    private final void reset(GL gl, int newSamples) throws GLException {
+        if(!initialized) {
+            // NOP if not yet initializes
+            return;
+        }
+                
+        final GLContext curContext = GLContext.getCurrent();
+        final GLContext ourContext = gl.getContext();
+        final boolean ctxSwitch = null != curContext && curContext != ourContext; 
+        if(DEBUG) {
+            System.err.println("GLFBODrawableImpl.reset(newSamples "+newSamples+"): BEGIN - ctxSwitch "+ctxSwitch+", "+this);
+            Thread.dumpStack();
+        }
+        Throwable tFBO = null;
+        Throwable tGL = null;
+        ourContext.makeCurrent();
+        fboBound = false; // clear bound-flag immediatly, caused by contextMadeCurrent(..) - otherwise we would swap @ release
+        try {                        
+            final int maxSamples = gl.getMaxRenderbufferSamples();        
+            newSamples = newSamples <= maxSamples ? newSamples : maxSamples;
+            
+            if(0==samples && 0<newSamples || 0<samples && 0==newSamples) {
+                // MSAA on/off switch
+                if(DEBUG) {
+                    System.err.println("GLFBODrawableImpl.reset(): samples [on/off] reconfig: "+samples+" -> "+newSamples);
+                }
+                initialize(false, gl);
+                samples = newSamples;
+                initialize(true, gl);
+            } else {            
+                if(DEBUG) {
+                    System.err.println("GLFBODrawableImpl.reset(): simple reconfig: "+samples+" -> "+newSamples);
+                }
+                final int nWidth = getWidth();
+                final int nHeight = getHeight();
+                samples = newSamples;
+                pendingFBOReset = ( 1 < fbos.length ) ? fbos[fboIFront] : null; // pending-front reset only w/ double buffering (or zero samples)
+                for(int i=0; i<fbos.length; i++) {
+                    if(1 == fbos.length || fboIFront != i) {
+                        reset(gl, fbos[i], i, nWidth, nHeight, samples);
+                    }
+                }
+                final GLCapabilities fboCapsNative = (GLCapabilities) surface.getGraphicsConfiguration().getChosenCapabilities();
+                fbos[0].formatToGLCapabilities(fboCapsNative);
+            }
+        } catch (Throwable t) {
+            tFBO = t;
+        } finally {
+            try {
+                ourContext.release();
+                if(ctxSwitch) {
+                    curContext.makeCurrent();
+                }
+            } catch (Throwable t) {
+                tGL = t;
+            }
+        }
+        if(null != tFBO) {
+            throw new GLException("GLFBODrawableImpl.reset(..) FBObject.reset(..) exception", tFBO);
+        }
+        if(null != tGL) {
+            throw new GLException("GLFBODrawableImpl.reset(..) GLContext.release() exception", tGL);
+        }
+        if(DEBUG) {
+            System.err.println("GLFBODrawableImpl.reset(newSamples "+newSamples+"): END "+this);
+        }
     }
     
+    //
+    // GLDrawable
+    //
     
     @Override
-    public GLContext createContext(GLContext shareWith) {
+    public final GLContext createContext(GLContext shareWith) {
         final GLContext ctx = parent.createContext(shareWith);
         ctx.setGLDrawable(this, false);
         return ctx;
     }
 
+    //
+    // GLDrawableImpl
+    //
+    
     @Override
-    public GLDynamicLookupHelper getGLDynamicLookupHelper() {
+    public final GLDynamicLookupHelper getGLDynamicLookupHelper() {
         return parent.getGLDynamicLookupHelper();
     }
 
     @Override
-    protected void swapBuffersImpl() {
-    }
+    protected final int getDefaultDrawFramebuffer() { return initialized ? fbos[fboIBack].getWriteFramebuffer() : 0; }
+    
+    @Override
+    protected final int getDefaultReadFramebuffer() { return initialized ? fbos[fboIFront].getReadFramebuffer() : 0; }
 
     @Override
-    protected void setRealizedImpl() {
+    protected final void setRealizedImpl() {
         parent.setRealized(realized);
-        if(realized) {    
-            final MutableGraphicsConfiguration msConfig = (MutableGraphicsConfiguration) surface.getGraphicsConfiguration();
-            final GLCapabilitiesImmutable chosenCaps = (GLCapabilitiesImmutable) msConfig.getChosenCapabilities();
-            final GLCapabilitiesImmutable chosenFBOCaps = GLGraphicsConfigurationUtil.fixOffscreenGLCapabilities(chosenCaps, true /*FBO*/, false /*PBO*/);    
-            msConfig.setChosenCapabilities(chosenFBOCaps);
+    }
+    
+    @Override
+    protected final void contextRealized(GLContext glc, boolean realized) {
+        initialize(realized, glc.getGL());
+    }
+    
+    @Override
+    protected final void contextMadeCurrent(GLContext glc, boolean current) {
+        final GL gl = glc.getGL();
+        if(current) {
+            fbos[fboIBack].bind(gl);
+            fboBound = true;
+        } else {
+            if(fboBound) {
+                swapFBOImpl(glc);
+                fboBound=false;
+                if(DEBUG) {
+                    System.err.println("Post FBO swap(@release): done");
+                }
+            }
         }
     }
-
+        
     @Override
-    public int getWidth() {
-        return width;
+    protected void swapBuffersImpl(boolean doubleBuffered) {
+        final GLContext ctx = GLContext.getCurrent();
+        if(null!=ctx && ctx.getGLDrawable()==this) {
+            if(fboBound) {
+                swapFBOImpl(ctx);
+                fboBound=false;
+                if(DEBUG) {
+                    System.err.println("Post FBO swap(@swap): done");
+                }
+            }
+        }
+        if(null != swapBufferContext) {
+            swapBufferContext.swapBuffers(doubleBuffered);
+        }
+    }
+    
+    private final void swapFBOImpl(GLContext glc) {
+        final GL gl = glc.getGL();
+        fbos[fboIBack].markUnbound(); // fast path, use(gl,..) is called below
+
+        // Safely reset the previous front FBO
+        if(null != pendingFBOReset) {
+            reset(gl, pendingFBOReset, fboIFront, getWidth(), getHeight(), samples);
+            pendingFBOReset = null;
+        }
+        
+        if(DEBUG) {
+            int _fboIFront = ( fboIFront + 1 ) % fbos.length;
+            if(_fboIFront != fboIBack) { throw new InternalError("XXX: "+_fboIFront+"!="+fboIBack); }
+        }
+        fboIFront = fboIBack;
+        fboIBack  = ( fboIBack  + 1 ) % fbos.length;
+        
+        final Colorbuffer colorbuffer = samples > 0 ? fbos[fboIFront].getSamplingSink() : fbos[fboIFront].getColorbuffer(0);
+        final TextureAttachment texAttachment;
+        if(colorbuffer instanceof TextureAttachment) {
+            texAttachment = (TextureAttachment) colorbuffer;
+        } else {
+            if(null == colorbuffer) {
+                throw new GLException("Front colorbuffer is null: samples "+samples+", "+this);
+            } else {
+                throw new GLException("Front colorbuffer is not a texture: "+colorbuffer.getClass().getName()+": samples "+samples+", "+colorbuffer+", "+this);
+            }
+        }
+        gl.glActiveTexture(GL.GL_TEXTURE0 + texUnit);
+        fbos[fboIFront].use(gl, texAttachment);
+        
+        /* Included in above use command:  
+                gl.glBindFramebuffer(GL2GL3.GL_DRAW_FRAMEBUFFER, fbos[fboIBack].getDrawFramebuffer());
+                gl.glBindFramebuffer(GL2GL3.GL_READ_FRAMEBUFFER, fbos[fboIFront].getReadFramebuffer());
+        } */
+        
+        if(DEBUG) {
+            System.err.println("Post FBO swap(X): fboI back "+fboIBack+", front "+fboIFront+", num "+fbos.length);
+        }
     }
 
+    //
+    // GLFBODrawable
+    // 
+    
+    @Override
+    public final boolean isInitialized() {
+        return initialized;
+    }
+    
     @Override
-    public int getHeight() {
-        return height;
+    public final void resetSize(GL gl) throws GLException {
+        reset(gl, samples);
     }    
+    
+    @Override
+    public final int getTextureUnit() { return texUnit; }
+    
+    @Override
+    public final void setTextureUnit(int u) { texUnit = u; }
+    
+    @Override
+    public final int getNumSamples() { return samples; }
+    
+    @Override
+    public void setNumSamples(GL gl, int newSamples) throws GLException {
+        if(samples != newSamples) {
+            reset(gl, newSamples);
+        }
+    }
+    
+    /** // TODO: Add or remove TEXTURE (only) DoubleBufferMode support
+    @Override
+    public final DoubleBufferMode getDoubleBufferMode() {
+        return doubleBufferMode;
+    }
+    
+    @Override
+    public final void setDoubleBufferMode(DoubleBufferMode mode) throws GLException {
+        if(initialized) {
+            throw new GLException("Not allowed past initialization: "+this);
+        }        
+        final GLCapabilitiesImmutable caps = (GLCapabilitiesImmutable) surface.getGraphicsConfiguration().getChosenCapabilities();
+        if(0 == samples && caps.getDoubleBuffered() && DoubleBufferMode.NONE != mode) {
+            doubleBufferMode = mode;
+        }
+    } */
+    
+    @Override
+    public FBObject getFBObject(int bufferName) throws IllegalArgumentException {
+        if(!initialized) {
+            return null;
+        }
+        final FBObject res;
+        switch(bufferName) {
+            case GL.GL_FRONT:
+                if( samples > 0 ) {
+                    res = fbos[0].getSamplingSinkFBO();
+                } else {
+                    res = fbos[fboIFront];
+                }
+                break;
+            case GL.GL_BACK:
+                res = fbos[fboIBack];
+                break;
+            default: 
+                throw new IllegalArgumentException(illegalBufferName+toHexString(bufferName));
+        }        
+        return res;  
+    }
+    
+    @Override
+    public final TextureAttachment getTextureBuffer(int bufferName) throws IllegalArgumentException {
+        if(!initialized) {
+            return null;
+        }
+        final TextureAttachment res;
+        switch(bufferName) {
+            case GL.GL_FRONT:
+                if( samples > 0 ) {
+                    res = fbos[0].getSamplingSink();
+                } else {
+                    res = (TextureAttachment) fbos[fboIFront].getColorbuffer(0);
+                }
+                break;
+            case GL.GL_BACK:
+                if( samples > 0 ) {
+                    throw new IllegalArgumentException("Cannot access GL_BACK buffer of MSAA FBO: "+this);
+                } else {
+                    res = (TextureAttachment) fbos[fboIBack].getColorbuffer(0);
+                }
+                break;
+            default: 
+                throw new IllegalArgumentException(illegalBufferName+toHexString(bufferName));
+        }        
+        return res;  
+    }
+    private static final String illegalBufferName = "Only GL_FRONT and GL_BACK buffer are allowed, passed ";
+    
+    @Override
+    public String toString() {
+        return getClass().getSimpleName()+"[Initialized "+initialized+", realized "+isRealized()+", texUnit "+texUnit+", samples "+samples+
+                ",\n\tFactory   "+getFactory()+
+                ",\n\tHandle    "+toHexString(getHandle())+
+                ",\n\tCaps      "+surface.getGraphicsConfiguration().getChosenCapabilities()+
+                ",\n\tfboI back "+fboIBack+", front "+fboIFront+", num "+(initialized ? fbos.length : 0)+
+                ",\n\tFBO front read "+getDefaultReadFramebuffer()+", "+getFBObject(GL.GL_FRONT)+
+                ",\n\tFBO back  write "+getDefaultDrawFramebuffer()+", "+getFBObject(GL.GL_BACK)+
+                ",\n\tSurface   "+getNativeSurface()+
+                "]";
+    }
+    
+    public static class ResizeableImpl extends GLFBODrawableImpl implements GLFBODrawable.Resizeable {
+        protected ResizeableImpl(GLDrawableFactoryImpl factory, GLDrawableImpl parent, ProxySurface surface, 
+                                 GLCapabilitiesImmutable fboCaps, int textureUnit) {
+            super(factory, parent, surface, fboCaps, textureUnit);
+        }
+        
+        @Override
+        public final void setSize(GLContext context, int newWidth, int newHeight) throws NativeWindowException, GLException {
+            if(DEBUG) {
+                System.err.println("GLFBODrawableImpl.ResizeableImpl setSize: ("+Thread.currentThread().getName()+"): "+newWidth+"x"+newHeight+" - surfaceHandle 0x"+Long.toHexString(getNativeSurface().getSurfaceHandle()));
+            }
+            int lockRes = lockSurface();
+            if (NativeSurface.LOCK_SURFACE_NOT_READY >= lockRes) {
+                throw new NativeWindowException("Could not lock surface: "+this);
+            }
+            try {
+                // propagate new size 
+                final ProxySurface ps = (ProxySurface) getNativeSurface();
+                final UpstreamSurfaceHook ush = ps.getUpstreamSurfaceHook();
+                if(ush instanceof UpstreamSurfaceHook.MutableSize) {
+                    ((UpstreamSurfaceHook.MutableSize)ush).setSize(newWidth, newHeight);
+                } else {
+                    throw new InternalError("GLFBODrawableImpl.ResizableImpl's ProxySurface doesn't hold a UpstreamSurfaceHookMutableSize but "+ush.getClass().getName()+", "+ps+", ush");
+                }
+                if( null != context && context.isCreated() ) {
+                    resetSize(context.getGL());
+                }
+            } finally {
+                unlockSurface();
+            }
+        }
+    }
 }