[Development] 2D Graphics Roadmap?

[Steve Gold]

Alan,

Thank you for your very informative response.

Please see my comments below.

Steve

-----Original Message----- 
From: Alan Alpert
Sent: Tuesday, January 28, 2014 2:43 PM
To: Steve Gold
Cc: Qt Development Group
Subject: Re: [Development] 2D Graphics Roadmap?

On Sat, Jan 25, 2014 at 12:10 PM, Steve Gold <steveg2357 at gmail.com> wrote:
> I'm relatively new to Qt (3-4 months now) and have learned a lot. However,
> I've been experimenting with developing apps with QML/JavaScript and
> Canvas/Context2D but have received suggestions to look at Scene Graph or
> Graphics View, both of which seem to require developing C++ classes. Is 
> this
> correct?
>
> QML appears to be a more "efficient" and "productive" approach from a
> development point of view but C++ seems to be more "powerful" and
> "expressive." The examples for Graphics View that I've looked at are the
> most extensive while the examples for Scene Graph and Canvas seem more
> simplistic.
>
> As an example, I found Graphics View demos called elasticnodes (moveable
> nodes/arc) and diagramscene (select/place items onto a palette) but 
> nothing
> remotely similar for the other graphics technologies. I've created several
> posts in the forums and even sent one email but haven't received any
> significant responses.
>
> Before I spend much more time, possibly in the wrong direction, can 
> someone
> address the future of Canvas, Graphics View and Scene Graph with respect 
> to
> Qt and Qt Creator? A comparison would be especially useful.

GraphicsView is a more mature framework, pretty much marked "done",
which is why it has the most examples. It's not going anywhere, which
probably also means don't expect big changes in performance or
underlying implementation. SceneGraph is fairly new, and Canvas is
even newer, depends on the level of maturity you prefer to work on.
I'd expect SceneGraph, and probably Canvas too, to mature more over
the life of Qt 5 (both are new in 5.0).

** Are there any roadmaps for Scene Graph or Canvas that discuss planned 
features or improvements?  Does saying "... probably Canvas too ..." mean 
that there is no definitive plan for the enhancement and evolution of 
Canvas?

GraphicsView and SceneGraph are both usable via QML or C++. You can
use C++ for complex custom elements, and compose simple ones out of
Rectangles or Images in QML.

** Scene Graph looks like it allows the creation of a set of backend C++ 
QQuickItem subclasses that can be referenced in QML but there don't appear 
to be many QML "Scene Graph types" that can be directly used within QML, 
except for ShaderEffect, Gradient and a few others . Creating Scene Graph 
C++ classes also looks to me like they take a lot of time and code to write 
compared to what I would expect from creating QML types. Please correct me 
if I'm wrong.

Note that all the QtQuick elements, even
Canvas, are implemented with SceneGraph, so you can mix and match them
freely. QtQuick 1, primarily available for compatibility reasons, uses
GraphicsView.


** You state "... even Canvas, are implemented with SceneGraph ..." but 
context2d.h and context2d.cpp use QPainter
    class Context2D : public QObject
    . . .
      QPainter m_painter;
      QPainterPath m_path;
    . . .
The post located at http://qt-project.org/forums/viewthread/37605/ states
    "Qt Quick 2 makes use of a dedicated scene graph based on OpenGL ES 2.0 
or OpenGL 2.0 for its rendering. Using a scene graph for graphics rather 
than
    the traditional imperative painting systems (QPainter and similar), 
means the scene to be rendered can be retained between frames and the 
complete set
    of primitives to render is known before rendering starts."
Can you please clarify this apparent discrepancy?

The current recommended approach is to use the new frameworks, build
your app in QML with QtQuick and use Canvas anywhere you need custom
2D rendering (possibly re-writing that element with SG C++ if it's
performance critical).

** It would be an achievement if Qt enabled users to write QML types for 
Canvas that used Scene Graph under the covers and did not require any 
rewriting in C++.

** Will Qt use Scene Graph for 3D graphics? Is anything in this area on the 
horizon for QML?

> Thanks.
>
> Steve
>
> BTW, I'm also posting this in the Qt forums

If you linked to that post, I could have easily checked it for possible 
overlap.

** The post is located at http://qt-project.org/forums/viewthread/37605/
--
Alan Alpert