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.).

3 files changed, 24 insertions, 31 deletions

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;