eean

In yesterday's blog I talked about my issue of wanting to use (animated) GraphicsView's in an Interview system for Amarok's playlist. Ivan ?uki? pointed me to a 2006 Trolltech Developer Days presentation about Advanced Item View. The presenter did show a pretty brute force way of doing animations in delegates, by just firing a timer every 40 ms. I tried this out two different ways.

First was similar to how he did it, firing a timer. It was not to my great surprise that this resulted in 30% CPU time for just one row needing to be animated, and it went up from there as additional rows were added It actually still looked and reacted fine though, so before I noticed the CPU usage I was feeling like I had cracked the case.

Then I tried it by connecting (indirectly, since I had to translate a QGraphicsScene into a QModelIndex) QGraphicsScene::sceneRectChanged to QAbstractItemView::update. However this didn't work. Apparently QGraphicsScene doesn't consider a flashing cursor as a scene change worth mentioning?

So now I'm basically back to where I was. Except the presentation did hold out another possibility of subclassing QAbstractItemView and then doing setViewport. This is what he did for the QGLWidget views that he made (instead of just writing a view from scratch). However its not quite clear to me what the QAbstractItemView provides when you override the viewport. More importantly none of the examples had scrolling, so they just painted the whole area all the time. And figuring that out is the biggest issue with perhaps using a QGraphicsView (whether by itself or as a viewport of a QAbstractItemView.)

More Playlist Details

Benjamin Meyer had a few questions about the playlist that I'll address here:

• I think Ben you know what the playlist does. The user queues up music to listen to and can also edit their tags.
• I see no reason for multiple views.
• Animations - yes. I don't know if I'll have time to do cool animations this summer, but I do want to have a framework in place where someone could implement nifty animations easily.
• Editing - currently the reason I want to get animations to work. Users can do some basic bulk tag editing using the playlist.
  
• As far as what the playlist looks like, its the thing on the right in Nikolaj's most recent blog. In the future we want to do more complicated things such as grouping tracks from the same albums together.
  
• Each row is a single cell, so the entire row is drawn in a single delegate paint. So the view itself is a fairly basic subclass of QListView.
  

Background Info

My Summer of Code project is to spruce up the playlist. My idea was to use Qt's new Interview system to make Amarok more memory efficient and less laggy even with large number of tracks in the playlist - performance of Amarok 1.x suffers noticeably with large playlists. This has largely worked out well.

To make the playlist look good I decided to use GraphicsView. So for the past month I've been using QGraphicsScene to paint the items in a QListView using a QAbstractItemDelegate subclass. The subclass overrides the ::paint method, which provides a QPainter. I send the painter to QGraphicsScene::render and it paints the item.

The problem

What I've come to find out is that QGraphicsScene render is really meant for printing, not for screen display. Since (you might have noticed) there's no QGraphicsView involved, there's nothing to translate normal QWidget events into their GraphicsView counterparts. After looking at qgraphicsview.cpp, I found it wasn't hard to simply put that sort of functionality into QListView. So currently double clicking works in QListView and you can initiate edits this way.

What initiating edits has made quite clear is that there animation's do not work (the cursor doesn't blink), and unlike with the event-translation issue, there is no clear solution. Without a QGraphicsView and with Delegate's simplistic painting system (which is all-or-nothing) I don't see how to do it easily.

Possible Solutions

Widgets Everywhere

Using some hack or another (setItemWidget, abusing the editor widget stuff, dark magic) I could make each item on the playlist a widget. Andrew of Skype (who attended aKademy) apparently has similar issues (wanting to use Interview, but with interactive custom widgets which you can see if you use Skype). He made it pretty clear to me that this was a life-sucking endeavour. It also has obvious efficiency issues... playlist items can't be QObjects due to memory issues, let alone QWidgets (though if there was some smart way to only have 100 qwidgets at a time that would work).

Overlay Editor Widget

Somehow overlay a text edit line just over the text that the user is editing. No idea if this is possible. And it doesn't allow any other animations to be used.

Pixie-dust the delegate or QListView to display the animations

Under the current regime, somehow let the delegate or the QListView know when and where it needs to repaint the QGraphicsScene to show the animations.

Replace QListView with a QGraphicsView

...and implement everything that QListView does in a QGraphicsView subclass. Really this is what I'm leaning towards at the moment. This would be very similar to what the Drill Down Example does, except with 100x the data.

One of the main benefits of Model/View is that it only has in memory the data being displayed. It doesn't really store any data, on every paint operation the View asks the Model for the data. I really don't know where to start on replicating this sort of functionality in QGraphicsView. Would I just constantly delete and add items as the user scrolls?

I would appreciate any suggestions. Whether its something (else) I've missed or how I would go about implementing the last solution.

Thanks!

Read the entire KDE development with Git thread yesterday. There's been a lot of talk of such things lately... Mark Shuttleworth made the point that using a system with easy branching could really change how we worked (and made it overly clear that he didn't mean that we should all use Bazaar).



Someone linked to a page which linked to Linus's Git talk. He gave KDE very high praise by calling us "not smart" (in having one big repo). Everyone else who disagreed with Linus was stupid and ugly. So that was neat.



The problem with Linus's talk is that he uses a "pull" method of development, where he pulls in patches or merges from Git. And he doesn't recognize any other methodology as having any value. It really wouldn't work for a project like KDE and probably most projects, since there would be no one to do the pulling. Linus's full time job is pretty much to decide what to pull into the kernel. It would just slow development down to have someone like that with KDE or Amarok. Really I guess Linus doesn't see the Linux development model as being very unique in the open source world, even though it is. Or maybe Linus is a bit like the Douglas Adam character who considers his house the "outside of the insane asylum" and the rest of the world the "insane asylum" - we're all just crazy.



SVK was surprisingly not mentioned much in the KDE thread. SVK does serve me pretty well for doing local commits and transversing through the history of Amarok (since I have all 9800+ commits of Amarok stored locally). But its not really distributed at all in the way Linus meant it... I can't easily share a branch, it'd require commiting to SVN. Also its quite a bit slower then SVN, which wasn't a speed demon to begin with.



The thread concluded that having parallel VCSs would be pretty horrible, since it would require people to learn more then one system and thereby increase the barrier of entry to KDE development. But also Dirk said he would be willing to help someone setup a Hg->SVN/SVN->Hg system.

My friend Ruth IMed me today and wondered how the trip to Scotland went. Which reminded me, I haven't blogged about all the photos I posted.



I think this photo sums up the experience of Scotland:





And as far as aKademy itself is concerned:



No explanation needed.



See the rest of the photos, including giraffes, Unionists parades and various hackers in my Flickr aKademy set.

So after a straightforward flight from Glasgow to Philadelphia to St. Louis, Missouri, I had a nice couple of days hanging out with Sherry. The important thing accomplished is that I installed Kubuntu Linux on her laptop. Its a dual-booting system (Windows is installed), but I did make sure that she has only 3 seconds to decide to boot into Windows instead of 10. Default OS being loaded made a pretty big difference back when I was a dual-booter.



Anyways when the school year starts and hopefully Amarok 2 will be somewhat usable, I'll have a convenient guinea pig way of doing user-testing.



Came back to my parents home in Fulton, Missouri to find my functional desktop greeting me. Its entire motherboard and CPU had been bad and were replaced. Took me last night and this morning to compile a kernel (ended up using basically the .config from the Gentoo Install CD, the default genkernel has no SATA support at all) and tweak the system a bit.



If I was going to install a new CPU and mobo I thought I might as well get an upgrade... now I have a AMD64 3800 x2 instead of just a AMD64 3800 (was pretty limited in choice from wanting to keep my current RAM). This makes my Icecream Monitor even more hypnotizing... though obviously nothing compared to the -j20 compiles I was doing at aKademy.

You should be able to click a "Find Music Video" button and have it search Google Video/YouTube/LastFm and have it play the music video for the current song.