Bug 975 - GLJPanel's OffscreenDrawable shall not double swap (custom swap by GLEventListener using [AWT]GLReadBufferUtil)
Summary: GLJPanel's OffscreenDrawable shall not double swap (custom swap by GLEventLis...
Alias: None
Product: Jogl
Classification: JogAmp
Component: awt (show other bugs)
Version: 2
Hardware: All all
: --- enhancement
Assignee: Sven Gothel
Depends on:
Reported: 2014-02-13 21:32 CET by Sven Gothel
Modified: 2014-08-30 20:04 CEST (History)
0 users

See Also:
Type: ---
SCM Refs:
908ebd99d1eb57ce773a1fdd67c76886da86b9e6 82f679b064784213591b460fc5eaa1f5f196fbd1 d46d9ad8f998a7128d9f023294d5f489673d6d8a 41190c3830157abdf9649cbf7767e57108f55075 b96fc594f15fcf9ee0fd238ce8d7a10aea781d32
Workaround: ---


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Description Sven Gothel 2014-02-13 21:32:12 CET
When utilizing [AWT]GLReadBufferUtil it is usually desired to read from the front-buffer
instead the back-buffer. The latter may not be defined, e.g. when using MSAA.

A GLEventListener utilizing [AWT]GLReadBufferUtil,
must perform the drawable.swapBuffers() to be able to read from the front-buffer.

Usually GLAutoDrawable.setAutoSwapBuffer(false) should be called here,
to avoid a double swap - however GLJPanel does not support toggling auto-swap
since it requires to control swap for it's own read-pixels.

Remedy for GLJPanel:
  - GLJPanel issues helper.setAutoSwapBufferMode(false) - immutable

  - Enable GLJPanel.swapBuffer() if initializes
    This was previously disabled.

  - GLJPanel's OffscreenBackend listens to  surfaceUpdated,
    to be notified whether postGL needs to swap buffer
    or the drawable.swapBuffer() was already called between preGL and postGL.

See unit tests adding/removing a snapshot GLEventListener
performing swapBuffers() and setting auto-swap accordingly.
Comment 1 Sven Gothel 2014-02-13 21:32:56 CET
  fixed as described
Comment 2 Sven Gothel 2014-02-14 06:39:05 CET
  GLJPanel: Use default auto-swap mechanims

    Refines commit 908ebd99d1eb57ce773a1fdd67c76886da86b9e6
    Note that the test case decide whether to auto-swap (after read-pixels)
    or not auto-swap (manual swap before read-pixels).
    See UITestCase.swapBuffersBeforeRead(GLCapabilitiesImmutable chosenCaps):
       Determines whether the chosen GLCapabilitiesImmutable requires a swap-buffers before reading pixels.
       Usually one uses the default-read-buffer, i.e. GL.GL_FRONT for single-buffer
       and GL.GL_BACK for double-buffer GLDrawables
       and GL.GL_COLOR_ATTACHMENT0 for offscreen framebuffer objects.
       Here swap-buffers shall happen after calling reading pixels, the default.
       However, multisampling offscreen GLFBODrawables utilize swap-buffers to downsample
       the multisamples into the readable sampling sink.
       In this case, we require a swap-buffers before reading pixels.
       Returns:  chosenCaps.isFBO() && chosenCaps.getSampleBuffers()
    - GLJPanel:
      - Remove SurfaceUpdatedListener mechanism in favor of
        default auto-swap-buffer via GLDrawableHelper.
        This removes complexity.
      - postGL does not need to perform explicit swapBuffer operation,
        but rely on GLDrawableHelper and the default mechanism.
        This is also compatible w/ J2D backend.
      - Use GLDrawableHelper for setAutoSwapBufferMode(..) and getAutoSwapBufferMode()
    - UITestCase:
      - Add 'boolean swapBuffersBeforeRead(GLCapabilitiesImmutable chosenCaps)'
        to determine whether swapBuffers() must occure before read-pixels. See above.
    - GLReadBuffer00Base*
      - remove explicit addSnapshotGLEL/removeSnapshotGLEL
      - add TextRendererGLEL, to display frame-count and -dimension
      - SnapshotGLEL*
        - simply toggle auto-swap in their init(..) and dispose(..) method!
        - clear back-buffer if 'swapBuffersBeforeRead'
          to test whether the right buffer is being used for read-pixels.
Comment 3 Sven Gothel 2014-02-18 19:13:39 CET
    Bug 975 - GLJPanel's OffscreenDrawable shall not double swap - Refine unit test for visual validation of 'no frame lag'
    To validate whether a 'display' command w/o animator results to the desired frame
    we introduce a 'userCounter' in TextRendererGLEL.
    The latter gets increased and maybe visually validated by a key-press -> display.
    Results: In all modes, MSAA or !MSAA, or flip - the result is valid.
    Tested on windows and linux.
Comment 4 Sven Gothel 2014-02-18 21:52:08 CET
   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:
      [1] - GL display
      [2] - GL swapBuffers (always due to single-buffer non-MSAA or MSAA offscreen drawable)
      [3] - readPixels
    Commit 82f679b064784213591b460fc5eaa1f5f196fbd1 however introduced:
      [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.).
Comment 5 Sven Gothel 2014-02-18 21:52:36 CET

   Pass hint whether dedicated read-drawable is being used (double buffering)
Comment 6 Sven Gothel 2014-08-30 19:43:54 CEST
Also related Bug 941 and Bug 1020
Comment 7 Sven Gothel 2014-08-30 20:04:02 CEST
Test cases: