qtdeclarative5-qtquick2-plugin should depend on libgl1-mesa-dri

Committed a fix to the packaging and put a raring build into qt5-beta-proper. I'd like to understand the problem itself a bit more closely though.

Ok, here comes my analysis:

 QSGRenderer::draw contains code like

    if (g->indexDataPattern() != QSGGeometry::AlwaysUploadPattern && g->indexCount() > 512) {
        // Base pointer for a VBO is 0
        indexData = 0;
        ...
    } else {
       ...
    }
    ....
    // draw the stuff...
    ...
    glDrawElements(g->drawingMode(), g->indexCount(), g->indexType(), indexData);

So in some cases uses a VBO passing indexData as 0

Without having libgl1-mesa-dri installed that crashes, with it installed it does not. My guess is that libgl1-mesa-dri adds VBO support and thus can interpret the 0 in indexData as a VBO instead of simply trying to access a NULL pointer

This bug was fixed in the package qtdeclarative-opensource-src - 5.0.2-1ubuntu1

---------------
qtdeclarative-opensource-src (5.0.2-1ubuntu1) saucy; urgency=low

  [ Timo Jyrinki ]
  * debian/patches/we_do_want_the_mouse_event_to_ourselves.patch:
    - Drop, merged upstream
  * debian/patches/fix_lp1087643.patch:
    - Drop, merged upstream
  * Merge with Debian experimental, remaining changes:
    - Keep architecture restrictions
    - Keep debian/patches/rendering_performance_fix_lp1092358.patch
  * Add libgl1-mesa-dri dependency for the quick2 plugin (LP: #1176199)
  * Cherry-pick listview crasher fixes from upstream 5.1 branch (LP: #1176962):
    - debian/patches/01_8563adb737cec5d440197ddbd514fe201c5f18ff_backport.patch
    - debian/patches/02_53e317468626284fe26877659dff551ce3bc0e55_backport.patch
    - debian/patches/03_51665a9ecaebaef2382c1e76ebedfeffacb4b3de_backport.patch
    - debian/patches/04_9d6cd72353e4862592c016951810abf9a7ab8079_backport.patch

  [ Lisandro Damián Nicanor Pérez Meyer ]
  * Fix wrong permissions of examples.

qtdeclarative-opensource-src (5.0.2-1) experimental; urgency=low

  * Initial release. (Closes: #697509)
 -- Timo Jyrinki <email address hidden> Mon, 29 Apr 2013 16:27:13 -0700

This dependency has unwanted consequences, as on ubuntu-touch (armhf, amd64, i386) or ubuntu-desktop (non-free drivers) mesa is not providing the gl implementation. It's managed by seeds else-wise, e.g. ubuntu-drivers-common / per-device seeds. Essentially, installations that do not have a valid gl implementation provided will not work, but it's not qtdeclarative5-qtquick2-plugin to pull one in, as it doesn't know which one it should be pulling in (e.g. hybris, mesa, nvidia, etc.).

How was the machine installed which didn't have any valid gl implementation available? Or alternatively, does qtdeclrative-opensource-src needs fixing / checking to work correctly with all gl implementations we care about? (android/hybris, mesa (native), nvidiat / ati). Cause libgl1-mesa-dri results in pulling in software Gallium3D rendereing on to ubuntu-touch devices which is about 40MB of dependencies, none of which we'd want to run (ever).

This was on the CI machines, no clue how they are installed.