Well, what means "view-engine" in the scope of Dolphin? The view-engine is responsible for showing the directory content as icons and text. In a very simplified form it can be seen as the sum of Dolphin's "icons mode", "details mode" and "columns mode".
The current version 1.7 of Dolphin is based on Qt's Interview Framework. Regarding the quality of the Interview Framework I'd like to quote a Qt developer from the Qt Labs Itemviews - The Next Generation article:
Having worked with the Interview Framework during the last four years I fully agree to this (... and probably would not have phrased it as friendly as in this quote ;-)). As an alternative for the Interview Framework a research project called Itemviews-NG has been created. After comparing Itemviews-NG with the view-engines-related code from libmeegotouch and Qt-Components it was clear that currently for Dolphin the Itemviews-NG would be the best choice. So the new view-engine for Dolphin 2.0 is build on a (very) modified subset of Itemviews-NG. In the longterm (probably with Qt 5) it is planned to integrate Qt-Quick but this affects only a non-critical minor part of the view-engine and has not high priority at the moment."Not surprising. If you are using Qt, chances are you are using the item views. And if you are using the item views, you are likely to have an opinion about them. While using these classes you may have even form the opinion that they are not exactly the most shining example of Qt quality framework and API design. Let’s just say that there is room for improvement, lots of room! The symptoms are clear: the framework is generally too slow, unstable and the API is difficult to use. A clear case of overly complex design."
So much talk about the new base of the view-engine, but which benefits get the users of Dolphin by this?
The new view-engine has been tested on a computer with a very slow hard-disk and developed with corner-cases in mind where the current view-engine had serious performance troubles. Now switching view-modes, zooming, resizing, ... is done with nearly no delay no matter how many items a directory has.
With Qt's Interview Framework having dynamic item-heights the way Dolphin required it was not possible. As workaround Dolphin used a fixed grid-size where the user could configure the maximum number of textlines. No matter which value has been used: Either the item-height got too large or the text got clipped like this:
Like most other filemanagers now also Dolphin is able to have dynamic item-sizes:
As a side-effect Dolphin 2.0 wastes less space and can show more items in parallel when using the same icon-size as the current Dolphin version.
Nonrectangular Item Boundaries
The Interview Framework only supports rectangular item boundaries. This means that moving the mouse above the position marked as red spot...
... results already in hovering the whole item:
The new view-engine provides optimized non-rectangular item boundaries:
So the hovering only takes place when the mouse pointer is above the the icon or text like in KDE 3 (Note that the look of the hovering is just a prototype and might change)
Grouping Support For All View Modes
Currently the "grouping" feature is only supported for the icons mode but will be available for all view-modes in Dolphin 2.0. I could not provide a screenshot yet as the code for grouping is still in a very early alpha-stage. In opposite to the current version of Dolphin grouping will not slow down the performance at all.
At the moment when removing or inserting items, changing the zoom-level or resizing the window the item-positions change magically from the original position to the new position. This sometimes makes it tricky for users to follow the new location of the items. With Dolphin 2.0 the layout-engine is fast enough to make those transitions animated. I don't like animations that slow-down the usage of an application so I took care to make them fast and unobtrusive.
From a developers point of view the new engine simplifies the maintenance a lot and lowers the barrier for developers to contribute patches for Dolphin. The code has been pushed to master today. Please note that the code is in an early alpha-stage and although the most tricky parts have been implemented already very basic things like drag and drop or selections have not been pushed yet. Those things are rather trivial to implement but it is still a lot of work and takes some time to have back the original feature-set. But I'm confident that everything will be ready until the 4.8 release of KDE Applications and hope that the new view-engine will justify the 2.0 version number :-)