Thread: Harmattan UI framework development is opened
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xynopsis is offline xynopsis
2010-02-19 , 10:49
Posts: 1 | Thanked: 4 times | Joined on Feb 2010 @ Helsinki, Finland
#25
Originally Posted by ezjd View Post
Since I didn't find place to discuss UI framework detail, I put some comments here (so it isn't as open as I expected ):

-- Why is the compositor based on QGLWidget instead of QWidget?
This implies that this UI framework requires HW OpenGL support all the time, similar to clutter.

This makes it less flexible when porting to a system w/o OpenGL and at least makes it more difficult to port as OpenGL driver is always closed source and not available from the beginning. (Actually, this is worst thing I think with Moblin).

-- Qt provides graphic system support, which make it possible to render using OpenGL or not. That is the flexibility I like with Qt. As such a fundamental component, using QWidget will provide more scalability. I like the idea in http://labs.trolltech.com/blogs/2009...e-an-overview/, which basically suggest to use SW raster engine by default and use QGLWidget when OpenGL acceleration is needed.
The Harmattan UI platform _is_ an OpenGL/GLES2-based platform and that backend is intentional. We are going to publish some validation test suites for hardware that can support our platform so this will not really be a big issue (e.g., GL extensions, shader support, etc).

Actually what Gunnar was talking in his blog is how off-screen painting is being handled. This is now made default in Qt i.e.,QPainter renders graphics to an off-screen buffer before displaying it on the framebuffer. The raster engine is of course the fastest off-screen painting approach because not all platform support GL rendering to pixmaps. Now how to render that off-screen buffer to the frame buffer is another issue, which of course the most efficient manner is by using GL.

Our compositor does not need to use raster because it completely bypasses QPainter since it is only interested in windows and already has the reference to off-screen representation of windows. What it needs is just a surface to draw to. That is why you see QGLWidget.
 

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