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[Zsombor Egri <1350863@xxxxxxxxxxxxxxxxxx>]

** Changed in: ubuntu-ui-toolkit (Ubuntu)
       Status: New => Fix Released

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https://bugs.launchpad.net/bugs/1350863

Title:
  UbuntuShape incompatible with Qt Scenegraph renderer batching strategy

Status in Ubuntu UI Toolkit:
  Fix Released
Status in ubuntu-ui-toolkit package in Ubuntu:
  Fix Released

Bug description:
  The default Qt Scenegraph renderer tries to assemble common primitives in the scenegraph into batches which it can use to reduce the number of draw calls and state changes. See 
  http://doc-snapshot.qt-project.org/qt5-5.3/qtquick-visualcanvas-scenegraph-renderer.html
  for more info.

  The UbuntuShape appears to break this batching behaviour.

  You can see how Qt selects batches by setting QSG_VISUALIZE=batches -
  the more unique colors you can see, the less good the batching and the
  more GL calls Qt needs to make to render your scene.

  Here is a file which shows good batching:

  import QtQuick 2.0

  Item {
      width: 400
      height: 400

      Grid {
          columns: 100
      Repeater {
          model: 1000
          delegate: Image {
                  source: "/usr/share/ubuntu-html5-ui-toolkit/0.1/ambiance/img/map_icon.png"
          }
      }
      }
  }

  If you run that with the QSG_VISUALIZE=batches variable set, you'll
  see just a block of color on screen - all the delegates were
  identified to share the same primitives and thus could be placed in
  one batch. If you run this example under apitrace, you'll notice that
  the number of GL calls is - once the batch is identified and uploaded,
  it takes under 50 GL calls to re-render everything. Sure it's a
  trivial example though.

  Now try:

  import QtQuick 2.0
  import Ubuntu.Components 0.1

  Item {
      width: 400
      height: 400

      Grid {
          columns: 100
      Repeater {
          model: 1000
          delegate: UbuntuShape {
              image: Image {
                  source: "/usr/share/ubuntu-html5-ui-toolkit/0.1/ambiance/img/map_icon.png"
              }
          }
      }
      }
  }

  and you'll see every delegate has a different color. This means Qt was
  unable to recognize that the delegates all had similar basis. If you
  run under apitrace, you'll see the GPU calls per frame are in the
  multiple thousands.

  We really suffer from this lack of batching in listviews or gridviews
  where each delegate uses an UbuntuShape.

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