[Development] 2D Graphics Roadmap?

[Alan Alpert]

On Tue, Jan 28, 2014 at 1:54 PM, Steve Gold <steveg2357 at gmail.com> wrote:
> 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/

I responded there, it's probably a more appropriate place for the
discussion and I'll stop duplicating it here.

--
Alan Alpert