Bug 975 - GLJPanel's OffscreenDrawable shall not double swap - Fix auto-swap mechanism ; Refined API doc getDefaultReadBuffer() ; Add GLDrawableUtil.swapBuffersBeforeRead(..)

Commit 82f679b064784213591b460fc5eaa1f5f196fbd1 which introduces the default swap-buffers
mechanism is erroneous:

The OffscreenBack backend requires the following operation order:

Order-1:
  [1] - GL display
  [2] - GL swapBuffers (always due to single-buffer non-MSAA or MSAA offscreen drawable)
  [3] - readPixels

+++

Commit 82f679b064784213591b460fc5eaa1f5f196fbd1 however introduced:

Order-2:
  [a] - GL display
  [b] - readPixels
  [c] - GL swapBuffers (always due to single-buffer non-MSAA or MSAA offscreen drawable)

since [a] and [b] happened in Updater's display method, and [c] followed the same
triggered by GLAutoDrawableHelper.

+++

The proof, commit d46d9ad8f998a7128d9f023294d5f489673d6d8a, is faulty,
since it always included the 'snapshot' GL event listener
which turned-off auto-swap and swapped before read-pixels.
TL;DR it enforced proper Order-1.

+++

This fix allows the Backend to intercept disable GLDrawableHelper's setAutoSwapBufferMode(..)
and perform the auto-swap mode itself in the proper Order-1.

The unit test has been refined to optionally disable the snapshot
to validate auto-swap mode.

+++

Refined GLBase and GLContext's API doc for 'getDefaultReadBuffer()'

+++

Add GLDrawableUtil.swapBuffersBeforeRead(..)
and reuse it for TileRendererBase (original impl.).

8 files changed, 133 insertions, 54 deletions

diff --git a/src/jogl/classes/com/jogamp/opengl/util/GLDrawableUtil.java b/src/jogl/classes/com/jogamp/opengl/util/GLDrawableUtil.java
index ec6d54d66..cf88e7bf6 100644
--- a/src/jogl/classes/com/jogamp/opengl/util/GLDrawableUtil.java
+++ b/src/jogl/classes/com/jogamp/opengl/util/GLDrawableUtil.java
@@ -30,6 +30,8 @@ package com.jogamp.opengl.util;
 import javax.media.nativewindow.AbstractGraphicsDevice;
 import javax.media.opengl.GLAnimatorControl;
 import javax.media.opengl.GLAutoDrawable;
+import javax.media.opengl.GLBase;
+import javax.media.opengl.GLCapabilitiesImmutable;
 import javax.media.opengl.GLContext;
 import javax.media.opengl.GLDrawable;
 import javax.media.opengl.GLEventListener;
@@ -168,4 +170,23 @@ public class GLDrawableUtil {
     if(bIsPaused) { bAnim.resume(); }
   }
 
+  /**
+   * Determines whether the chosen {@link GLCapabilitiesImmutable}
+   * requires a {@link GLDrawable#swapBuffers() swap-buffers}
+   * before reading pixels.
+   * <p>
+   * Usually one uses the {@link GLBase#getDefaultReadBuffer() default-read-buffer}
+   * in which case {@link GLDrawable#swapBuffers() swap-buffers} shall happen <b>after</b> calling reading pixels, the default.
+   * </p>
+   * <p>
+   * However, <i>multisampling</i> offscreen {@link javax.media.opengl.GLFBODrawable}s
+   * utilize {@link GLDrawable#swapBuffers() swap-buffers} to <i>downsample</i>
+   * the multisamples into the readable sampling sink.
+   * In this case, we require {@link GLDrawable#swapBuffers() swap-buffers} <b>before</b> reading pixels.
+   * </p>
+   * @return chosenCaps.isFBO() && chosenCaps.getSampleBuffers()
+   */
+  public static final boolean swapBuffersBeforeRead(final GLCapabilitiesImmutable chosenCaps) {
+      return chosenCaps.isFBO() && chosenCaps.getSampleBuffers();
+  }
 }
diff --git a/src/jogl/classes/com/jogamp/opengl/util/TileRendererBase.java b/src/jogl/classes/com/jogamp/opengl/util/TileRendererBase.java
index 22f5c017c..dabde83dd 100644
--- a/src/jogl/classes/com/jogamp/opengl/util/TileRendererBase.java
+++ b/src/jogl/classes/com/jogamp/opengl/util/TileRendererBase.java
@@ -412,22 +412,11 @@ public abstract class TileRendererBase {
      * requires a <i>pre-{@link GLDrawable#swapBuffers() swap-buffers}</i>
      * before accessing the results, i.e. before {@link #endTile(GL)}.
      * <p>
-     * Usually one uses the {@link GL#getDefaultReadBuffer() default-read-buffer}, i.e.
-     * {@link GL#GL_FRONT} for single-buffer and {@link GL#GL_BACK} for double-buffer {@link GLDrawable}s
-     * and {@link GL#GL_COLOR_ATTACHMENT0} for offscreen framebuffer objects.<br>
-     * Here {@link GLDrawable#swapBuffers() swap-buffers} shall happen <b>after</b> calling {@link #endTile(GL)}, the default.
+     * See {@link GLDrawableUtil#swapBuffersBeforeRead(GLCapabilitiesImmutable)}.
      * </p>
-     * <p>
-     * However, <i>multisampling</i> offscreen {@link GLFBODrawable}s
-     * utilize {@link GLDrawable#swapBuffers() swap-buffers} to <i>downsample</i>
-     * the multisamples into the readable sampling sink.
-     * In this case, we require a {@link GLDrawable#swapBuffers() swap-buffers} <b>before</b> calling {@link #endTile(GL)}.
-     * </p>
-     * @param chosenCaps the chosen {@link GLCapabilitiesImmutable}
-     * @return chosenCaps.isFBO() && chosenCaps.getSampleBuffers()
      */
     public final boolean reqPreSwapBuffers(GLCapabilitiesImmutable chosenCaps) {
-        return chosenCaps.isFBO() && chosenCaps.getSampleBuffers();
+        return GLDrawableUtil.swapBuffersBeforeRead(chosenCaps);
     }
 
     /**
diff --git a/src/jogl/classes/javax/media/opengl/GLBase.java b/src/jogl/classes/javax/media/opengl/GLBase.java
index 2d6aed139..3f0c77949 100644
--- a/src/jogl/classes/javax/media/opengl/GLBase.java
+++ b/src/jogl/classes/javax/media/opengl/GLBase.java
@@ -627,14 +627,24 @@ public interface GLBase {
     * Returns the default color buffer within the current bound
     * {@link #getDefaultReadFramebuffer()}, i.e. GL_READ_FRAMEBUFFER,
     * which will be used as the source for pixel reading commands,
-    * like {@link GL#glReadPixels(int, int, int, int, int, int, java.nio.Buffer)} etc.
+    * like {@link GL#glReadPixels(int, int, int, int, int, int, java.nio.Buffer) glReadPixels} etc.
     * <p>
     * For offscreen framebuffer objects this is {@link GL#GL_COLOR_ATTACHMENT0},
     * otherwise this is {@link GL#GL_FRONT} for single buffer configurations
     * and {@link GL#GL_BACK} for double buffer configurations.
     * </p>
+    * <p>
+    * Note-1: Neither ES1 nor ES2 supports selecting the read buffer via glReadBuffer
+    * and {@link GL#GL_BACK} is the default.
+    * </p>
+    * <p>
+    * Note-2: ES3 only supports {@link GL#GL_BACK}, {@link GL#GL_NONE} or {@link GL#GL_COLOR_ATTACHMENT0}+i
+    * </p>
+    * <p>
+    * Note-3: See {@link com.jogamp.opengl.util.GLDrawableUtil#swapBuffersBeforeRead(GLCapabilitiesImmutable) swapBuffersBeforeRead}
+    * for read-pixels and swap-buffers implications.
+    * </p>
     */
    public int getDefaultReadBuffer();
-
 }
 
diff --git a/src/jogl/classes/javax/media/opengl/GLContext.java b/src/jogl/classes/javax/media/opengl/GLContext.java
index 9245d10c2..9a4311772 100644
--- a/src/jogl/classes/javax/media/opengl/GLContext.java
+++ b/src/jogl/classes/javax/media/opengl/GLContext.java
@@ -1277,12 +1277,23 @@ public abstract class GLContext {
    * Returns the default color buffer within the current bound
    * {@link #getDefaultReadFramebuffer()}, i.e. GL_READ_FRAMEBUFFER​,
    * which will be used as the source for pixel reading commands,
-   * like {@link GL#glReadPixels(int, int, int, int, int, int, java.nio.Buffer)} etc.
+   * like {@link GL#glReadPixels(int, int, int, int, int, int, java.nio.Buffer) glReadPixels} etc.
    * <p>
    * For offscreen framebuffer objects this is {@link GL#GL_COLOR_ATTACHMENT0},
    * otherwise this is {@link GL#GL_FRONT} for single buffer configurations
    * and {@link GL#GL_BACK} for double buffer configurations.
    * </p>
+   * <p>
+   * Note-1: Neither ES1 nor ES2 supports selecting the read buffer via glReadBuffer
+   * and {@link GL#GL_BACK} is the default.
+   * </p>
+   * <p>
+   * Note-2: ES3 only supports {@link GL#GL_BACK}, {@link GL#GL_NONE} or {@link GL#GL_COLOR_ATTACHMENT0}+i
+   * </p>
+   * <p>
+   * Note-3: See {@link com.jogamp.opengl.util.GLDrawableUtil#swapBuffersBeforeRead(GLCapabilitiesImmutable) swapBuffersBeforeRead}
+   * for read-pixels and swap-buffers implications.
+   * </p>
    */
   public abstract int getDefaultReadBuffer();
 
diff --git a/src/jogl/classes/javax/media/opengl/awt/GLJPanel.java b/src/jogl/classes/javax/media/opengl/awt/GLJPanel.java
index c80b405b5..adc0a0d23 100644
--- a/src/jogl/classes/javax/media/opengl/awt/GLJPanel.java
+++ b/src/jogl/classes/javax/media/opengl/awt/GLJPanel.java
@@ -60,6 +60,7 @@ import java.util.List;
 
 import javax.media.nativewindow.AbstractGraphicsDevice;
 import javax.media.nativewindow.NativeSurface;
+import javax.media.nativewindow.SurfaceUpdatedListener;
 import javax.media.nativewindow.WindowClosingProtocol;
 import javax.media.opengl.GL;
 import javax.media.opengl.GL2;
@@ -223,6 +224,8 @@ public class GLJPanel extends JPanel implements AWTGLAutoDrawable, WindowClosing
   }
 
   private final GLDrawableHelper helper;
+  private boolean autoSwapBufferMode;
+
   private volatile boolean isInitialized;
 
   //
@@ -357,6 +360,7 @@ public class GLJPanel extends JPanel implements AWTGLAutoDrawable, WindowClosing
     if( null != shareWith ) {
         helper.setSharedContext(null, shareWith);
     }
+    autoSwapBufferMode = helper.getAutoSwapBufferMode();
 
     this.setFocusable(true); // allow keyboard input!
     this.addHierarchyListener(hierarchyListener);
@@ -944,12 +948,22 @@ public class GLJPanel extends JPanel implements AWTGLAutoDrawable, WindowClosing
 
   @Override
   public void setAutoSwapBufferMode(boolean enable) {
-    helper.setAutoSwapBufferMode(enable);
+    this.autoSwapBufferMode = enable;
+    boolean backendHandlesSwapBuffer = false;
+    if( isInitialized ) {
+        final Backend b = backend;
+        if ( null != b ) {
+            backendHandlesSwapBuffer= b.handlesSwapBuffer();
+        }
+    }
+    if( !backendHandlesSwapBuffer ) {
+        helper.setAutoSwapBufferMode(enable);
+    }
   }
 
   @Override
   public boolean getAutoSwapBufferMode() {
-    return helper.getAutoSwapBufferMode();
+    return autoSwapBufferMode;
   }
 
   @Override
@@ -1355,6 +1369,14 @@ public class GLJPanel extends JPanel implements AWTGLAutoDrawable, WindowClosing
     public boolean preGL(Graphics g);
 
     /**
+     * Return true if backend handles 'swap buffer' itself
+     * and hence the helper's setAutoSwapBuffer(enable) shall not be called.
+     * In this case {@link GLJPanel#autoSwapBufferMode} is being used
+     * in the backend to determine whether to swap buffers or not.
+     */
+    public boolean handlesSwapBuffer();
+
+    /**
      * Shall invoke underlying drawable's swapBuffer.
      */
     public void swapBuffers();
@@ -1394,6 +1416,7 @@ public class GLJPanel extends JPanel implements AWTGLAutoDrawable, WindowClosing
 
     private volatile GLContextImpl offscreenContext; // volatile: avoid locking for read-only access
     private boolean flipVertical;
+    private int frameCount = 0;
 
     // For saving/restoring of OpenGL state during ReadPixels
     private final GLPixelStorageModes psm =  new GLPixelStorageModes();
@@ -1417,7 +1440,7 @@ public class GLJPanel extends JPanel implements AWTGLAutoDrawable, WindowClosing
     @Override
     public final void initialize() {
       if(DEBUG) {
-          System.err.println(getThreadName()+": OffscreenBackend: initialize()");
+          System.err.println(getThreadName()+": OffscreenBackend: initialize() - frameCount "+frameCount);
       }
       try {
           final GLContext[] shareWith = { null };
@@ -1430,10 +1453,20 @@ public class GLJPanel extends JPanel implements AWTGLAutoDrawable, WindowClosing
                                                     chooser,
                                                     panelWidth, panelHeight);
           offscreenDrawable.setRealized(true);
+          if( DEBUG ) {
+              offscreenDrawable.getNativeSurface().addSurfaceUpdatedListener(new SurfaceUpdatedListener() {
+                  @Override
+                  public final void surfaceUpdated(Object updater, NativeSurface ns, long when) {
+                      System.err.println(getThreadName()+": OffscreenBackend.swapBuffers - frameCount "+frameCount);
+                  } } );
+          }
+
           offscreenContext = (GLContextImpl) offscreenDrawable.createContext(shareWith[0]);
           offscreenContext.setContextCreationFlags(additionalCtxCreationFlags);
           if( GLContext.CONTEXT_NOT_CURRENT < offscreenContext.makeCurrent() ) {
               isInitialized = true;
+              helper.setAutoSwapBufferMode(false); // we handle swap-buffers, see handlesSwapBuffer()
+
               final GL gl = offscreenContext.getGL();
               flipVertical = !GLJPanel.this.skipGLOrientationVerticalFlip && offscreenDrawable.isGLOriented();
               final GLCapabilitiesImmutable chosenCaps = offscreenDrawable.getChosenGLCapabilities();
@@ -1493,7 +1526,7 @@ public class GLJPanel extends JPanel implements AWTGLAutoDrawable, WindowClosing
     @Override
     public final void destroy() {
       if(DEBUG) {
-          System.err.println(getThreadName()+": OffscreenBackend: destroy() - offscreenContext: "+(null!=offscreenContext)+" - offscreenDrawable: "+(null!=offscreenDrawable));
+          System.err.println(getThreadName()+": OffscreenBackend: destroy() - offscreenContext: "+(null!=offscreenContext)+" - offscreenDrawable: "+(null!=offscreenDrawable)+" - frameCount "+frameCount);
       }
       if ( null != offscreenContext && offscreenContext.isCreated() ) {
         if( GLContext.CONTEXT_NOT_CURRENT < offscreenContext.makeCurrent() ) {
@@ -1554,6 +1587,11 @@ public class GLJPanel extends JPanel implements AWTGLAutoDrawable, WindowClosing
     }
 
     @Override
+    public final boolean handlesSwapBuffer() {
+        return true;
+    }
+
+    @Override
     public final void swapBuffers() {
         final GLDrawable d = offscreenDrawable;
         if( null != d ) {
@@ -1564,9 +1602,14 @@ public class GLJPanel extends JPanel implements AWTGLAutoDrawable, WindowClosing
     @Override
     public final void postGL(Graphics g, boolean isDisplay) {
       if (isDisplay) {
-        // offscreenDrawable is already swapped,
-        // either by GLDrawableHelper.invoke or user's GLEL according to auto-swap-buffer-mode.
-
+        if(DEBUG) {
+            System.err.println(getThreadName()+": GLJPanel.OffscreenBackend.postGL.0: - frameCount "+frameCount);
+        }
+        if( autoSwapBufferMode ) {
+            // Since we only use a single-buffer non-MSAA or double-buffered MSAA offscreenDrawable,
+            // we can always swap!
+            offscreenDrawable.swapBuffers();
+        }
         final GL gl = offscreenContext.getGL();
 
         final int componentCount;
@@ -1645,6 +1688,9 @@ public class GLJPanel extends JPanel implements AWTGLAutoDrawable, WindowClosing
         }
 
         // Must now copy pixels from offscreen context into surface
+        if(DEBUG) {
+            System.err.println(getThreadName()+": GLJPanel.OffscreenBackend.postGL.readPixels: - frameCount "+frameCount);
+        }
 
         // Save current modes
         psm.setAlignment(gl, alignment, alignment);
@@ -1731,9 +1777,13 @@ public class GLJPanel extends JPanel implements AWTGLAutoDrawable, WindowClosing
       helper.invokeGL(offscreenDrawable, offscreenContext, updaterDisplayAction, updaterInitAction);
 
       if ( null != alignedImage ) {
+        if( DEBUG ) {
+            System.err.println(getThreadName()+": GLJPanel.OffscreenBackend.doPaintComponent.drawImage: - frameCount "+frameCount);
+        }
         // Draw resulting image in one shot
         g.drawImage(alignedImage, 0, 0, alignedImage.getWidth(), alignedImage.getHeight(), null); // Null ImageObserver since image data is ready.
       }
+      frameCount++;
     }
 
     @Override
@@ -2078,6 +2128,11 @@ public class GLJPanel extends JPanel implements AWTGLAutoDrawable, WindowClosing
     }
 
     @Override
+    public final boolean handlesSwapBuffer() {
+        return false;
+    }
+
+    @Override
     public final void swapBuffers() {
         final GLDrawable d = joglDrawable;
         if( null != d ) {
diff --git a/src/test/com/jogamp/opengl/test/junit/jogl/acore/TestGLReadBuffer01GLJPanelAWT.java b/src/test/com/jogamp/opengl/test/junit/jogl/acore/TestGLReadBuffer01GLJPanelAWT.java
index 58ca24453..5853087f5 100644
--- a/src/test/com/jogamp/opengl/test/junit/jogl/acore/TestGLReadBuffer01GLJPanelAWT.java
+++ b/src/test/com/jogamp/opengl/test/junit/jogl/acore/TestGLReadBuffer01GLJPanelAWT.java
@@ -54,6 +54,7 @@ import com.jogamp.opengl.test.junit.jogl.demos.es2.GearsES2;
 import com.jogamp.opengl.test.junit.util.MiscUtils;
 import com.jogamp.opengl.test.junit.util.UITestCase;
 import com.jogamp.opengl.util.Animator;
+import com.jogamp.opengl.util.GLDrawableUtil;
 import com.jogamp.opengl.util.awt.AWTGLReadBufferUtil;
 import com.jogamp.opengl.util.texture.TextureIO;
 
@@ -74,7 +75,7 @@ public class TestGLReadBuffer01GLJPanelAWT extends GLReadBuffer00Base {
         final Dimension d = new Dimension(320, 240);
         final GLJPanel glad = createGLJPanel(skipGLOrientationVerticalFlip, useSwingDoubleBuffer, caps, d);
         final TextRendererGLEL textRendererGLEL = new TextRendererGLEL();
-        final SnapshotGLELAWT snapshotGLEL = new SnapshotGLELAWT(textRendererGLEL, awtGLReadBufferUtil, skipGLOrientationVerticalFlip);
+        final SnapshotGLELAWT snapshotGLEL = doSnapshot ? new SnapshotGLELAWT(textRendererGLEL, awtGLReadBufferUtil, skipGLOrientationVerticalFlip) : null;
         try {
             javax.swing.SwingUtilities.invokeAndWait(new Runnable() {
                 public void run() {
@@ -90,7 +91,9 @@ public class TestGLReadBuffer01GLJPanelAWT extends GLReadBuffer00Base {
                     glad.addGLEventListener(gears);
                     textRendererGLEL.setFlipVerticalInGLOrientation(skipGLOrientationVerticalFlip);
                     glad.addGLEventListener(textRendererGLEL);
-                    glad.addGLEventListener(snapshotGLEL);
+                    if( doSnapshot ) {
+                        glad.addGLEventListener(snapshotGLEL);
+                    }
                     panel.add(glad);
                     frame.pack();
                     frame.setVisible(true);
@@ -133,7 +136,9 @@ public class TestGLReadBuffer01GLJPanelAWT extends GLReadBuffer00Base {
                     } } );
             try { Thread.sleep(duration); } catch (InterruptedException e) { }
 
-            glad.disposeGLEventListener(snapshotGLEL, true /* remove */);
+            if( doSnapshot ) {
+                glad.disposeGLEventListener(snapshotGLEL, true /* remove */);
+            }
             final Animator anim = new Animator(glad);
             anim.start();
             try { Thread.sleep(2*duration); } catch (InterruptedException e) { }
@@ -181,7 +186,7 @@ public class TestGLReadBuffer01GLJPanelAWT extends GLReadBuffer00Base {
         @Override
         public void init(GLAutoDrawable drawable) {
             defAutoSwapMode = drawable.getAutoSwapBufferMode();
-            swapBuffersBeforeRead = UITestCase.swapBuffersBeforeRead(drawable.getChosenGLCapabilities());
+            swapBuffersBeforeRead = GLDrawableUtil.swapBuffersBeforeRead(drawable.getChosenGLCapabilities());
             drawable.setAutoSwapBufferMode( !swapBuffersBeforeRead );
         }
         @Override
@@ -229,6 +234,7 @@ public class TestGLReadBuffer01GLJPanelAWT extends GLReadBuffer00Base {
     };
 
     static GLCapabilitiesImmutable caps = null;
+    static boolean doSnapshot = true;
     static boolean keyFrame = false;
 
     public static void main(String[] args) {
@@ -238,6 +244,8 @@ public class TestGLReadBuffer01GLJPanelAWT extends GLReadBuffer00Base {
                 duration = MiscUtils.atol(args[i], duration);
             } else if(args[i].equals("-keyFrame")) {
                 keyFrame = true;
+            } else if(args[i].equals("-noSnapshot")) {
+                doSnapshot = false;
             }
         }
         org.junit.runner.JUnitCore.main(TestGLReadBuffer01GLJPanelAWT.class.getName());
diff --git a/src/test/com/jogamp/opengl/test/junit/jogl/acore/TestGLReadBuffer01GLWindowNEWT.java b/src/test/com/jogamp/opengl/test/junit/jogl/acore/TestGLReadBuffer01GLWindowNEWT.java
index af5ff2a1a..8cfb18f79 100644
--- a/src/test/com/jogamp/opengl/test/junit/jogl/acore/TestGLReadBuffer01GLWindowNEWT.java
+++ b/src/test/com/jogamp/opengl/test/junit/jogl/acore/TestGLReadBuffer01GLWindowNEWT.java
@@ -47,6 +47,7 @@ import com.jogamp.opengl.test.junit.jogl.demos.es2.GearsES2;
 import com.jogamp.opengl.test.junit.util.MiscUtils;
 import com.jogamp.opengl.test.junit.util.UITestCase;
 import com.jogamp.opengl.util.Animator;
+import com.jogamp.opengl.util.GLDrawableUtil;
 import com.jogamp.opengl.util.GLReadBufferUtil;
 import com.jogamp.opengl.util.texture.TextureIO;
 
@@ -68,7 +69,7 @@ public class TestGLReadBuffer01GLWindowNEWT extends GLReadBuffer00Base {
         final GLReadBufferUtil glReadBufferUtil = new GLReadBufferUtil(false, false);
         final GLWindow glad= GLWindow.create(caps);
         final TextRendererGLEL textRendererGLEL = new TextRendererGLEL();
-        final SnapshotGLEL snapshotGLEL = new SnapshotGLEL(textRendererGLEL, glReadBufferUtil);
+        final SnapshotGLEL snapshotGLEL = doSnapshot ? new SnapshotGLEL(textRendererGLEL, glReadBufferUtil) : null;
         try {
             glad.setPosition(64, 64);
             glad.setSize(320, 240);
@@ -77,7 +78,9 @@ public class TestGLReadBuffer01GLWindowNEWT extends GLReadBuffer00Base {
             glad.addGLEventListener(gears);
             textRendererGLEL.setFlipVerticalInGLOrientation(skipGLOrientationVerticalFlip);
             glad.addGLEventListener(textRendererGLEL);
-            glad.addGLEventListener(snapshotGLEL);
+            if( doSnapshot ) {
+                glad.addGLEventListener(snapshotGLEL);
+            }
             glad.setVisible(true);
         } catch( Throwable throwable ) {
             throwable.printStackTrace();
@@ -104,7 +107,9 @@ public class TestGLReadBuffer01GLWindowNEWT extends GLReadBuffer00Base {
             glad.setSize(size0.getWidth(), size0.getHeight());
             try { Thread.sleep(duration); } catch (InterruptedException e) { }
 
-            glad.disposeGLEventListener(snapshotGLEL, true /* remove */);
+            if( doSnapshot ) {
+                glad.disposeGLEventListener(snapshotGLEL, true /* remove */);
+            }
             final Animator anim = new Animator(glad);
             anim.start();
             try { Thread.sleep(2*duration); } catch (InterruptedException e) { }
@@ -133,7 +138,7 @@ public class TestGLReadBuffer01GLWindowNEWT extends GLReadBuffer00Base {
         @Override
         public void init(GLAutoDrawable drawable) {
             defAutoSwapMode = drawable.getAutoSwapBufferMode();
-            swapBuffersBeforeRead = UITestCase.swapBuffersBeforeRead(drawable.getChosenGLCapabilities());
+            swapBuffersBeforeRead = GLDrawableUtil.swapBuffersBeforeRead(drawable.getChosenGLCapabilities());
             drawable.setAutoSwapBufferMode( !swapBuffersBeforeRead );
         }
         @Override
@@ -170,6 +175,7 @@ public class TestGLReadBuffer01GLWindowNEWT extends GLReadBuffer00Base {
     };
 
     static GLCapabilitiesImmutable caps = null;
+    static boolean doSnapshot = true;
     static boolean keyFrame = false;
 
     public static void main(String[] args) {
@@ -179,6 +185,8 @@ public class TestGLReadBuffer01GLWindowNEWT extends GLReadBuffer00Base {
                 duration = MiscUtils.atol(args[i], duration);
             } else if(args[i].equals("-keyFrame")) {
                 keyFrame = true;
+            } else if(args[i].equals("-noSnapshot")) {
+                doSnapshot = false;
             }
         }
         org.junit.runner.JUnitCore.main(TestGLReadBuffer01GLWindowNEWT.class.getName());
diff --git a/src/test/com/jogamp/opengl/test/junit/util/UITestCase.java b/src/test/com/jogamp/opengl/test/junit/util/UITestCase.java
index 79c76e49f..a08e9f842 100644
--- a/src/test/com/jogamp/opengl/test/junit/util/UITestCase.java
+++ b/src/test/com/jogamp/opengl/test/junit/util/UITestCase.java
@@ -277,29 +277,6 @@ public abstract class UITestCase {
 
     static final String unsupportedTestMsg = "Test not supported on this platform.";
 
-    /**
-     * Determines whether the chosen {@link GLCapabilitiesImmutable}
-     * requires a {@link GLDrawable#swapBuffers() swap-buffers}
-     * before reading pixels.
-     * <p>
-     * Usually one uses the {@link GL#getDefaultReadBuffer() default-read-buffer}, i.e.
-     * {@link GL#GL_FRONT} for single-buffer and {@link GL#GL_BACK} for double-buffer {@link GLDrawable}s
-     * and {@link GL#GL_COLOR_ATTACHMENT0} for offscreen framebuffer objects.<br>
-     * Here {@link GLDrawable#swapBuffers() swap-buffers} shall happen <b>after</b> calling reading pixels, the default.
-     * </p>
-     * <p>
-     * However, <i>multisampling</i> offscreen {@link javax.media.opengl.GLFBODrawable}s
-     * utilize {@link GLDrawable#swapBuffers() swap-buffers} to <i>downsample</i>
-     * the multisamples into the readable sampling sink.
-     * In this case, we require a {@link GLDrawable#swapBuffers() swap-buffers} <b>before</b> reading pixels.
-     * </p>
-     * @param chosenCaps the chosen {@link GLCapabilitiesImmutable}
-     * @return chosenCaps.isFBO() && chosenCaps.getSampleBuffers()
-     */
-    public static final boolean swapBuffersBeforeRead(GLCapabilitiesImmutable chosenCaps) {
-        return chosenCaps.isFBO() && chosenCaps.getSampleBuffers();
-    }
-
     public String getSnapshotFilename(int sn, String postSNDetail, GLCapabilitiesImmutable caps, int width, int height, boolean sinkHasAlpha, String fileSuffix, String destPath) {
         if(null == fileSuffix) {
             fileSuffix = TextureIO.PNG;