[Qgis-developer] Changing ergonomy of the visibility of layers inside groups ?

[Even Rouault]

Hi,

I've been involved in discussions about improving/changing how visibility of 
layers (or groups) is handled when they are inside groups. Currently if you 
check/uncheck a group, this recursively checks/unchecks all its items (layers 
or sub-groups). There are workflows with large projects that include ~ 50 
layers in several groups and where users need to quicly turn on/off the 
visibility of groups, but when they don't want to change the visible of items 
inside the group. For those use cases, the layer themes functionnality has 
been tested but doesn't solve the need to be able to quickly (1 click) turn 
on/off/on/off the visibility of a group to be able to detect changes between 
raster imagery (the human eye is sensitive to movements more than colors), and 
they don't really have predefined configurations (would require creating tens of 
them)

Basically what is proposed is the following:

[ ] Group
	[x] Layer 1   --> Layer checked but group is not --> invisible
	[  ] Layer 2

[x] Group
	[x] Layer 1   --> Layer checked and group too --> visible
	[  ] Layer 2

There's a ticket https://hub.qgis.org/issues/14547 about that.

In the ticket it is suggested that the current behaviour might be preserved by 
using control-click. Control-click on a group would check/uncheck recursively 
all sub-items.

One effect of this change is that there wouldn't be anymore a tri-state for a 
group. It is either checked or unchecked. One potential downside of the new 
behaviour would be that it might not be immediately obvious to determine the 
visibility of a layer if you have several levels of hiearchy : looking only at 
the layer item if it is checked isn't sufficient to tell about its visibility. 
Not sure if that's an issue though (and if so what could be ways of indicating 
the visibility state)

At the API level, from what I can see,
* Qt::CheckState QgsLayerTreeGroup::isVisible() would be renamed to bool 
isChecked() since it would be a binary state and not related to visibility. 
I'm not sure if there are users outside of the layer tree mechanism where we 
really need to want if a group is visible (ie all its subgroups and layers are 
visible ?). Wouldn't be hard to implement anyway
* Qt::CheckState QgsLayerTreeLayer::isVisible() would be "split" into a bool 
isChecked() and a bool isVisible(). The later would inspect recursively its 
parents to figure out the final visibility state.

Thoughts ?

Even


-- 
Spatialys - Geospatial professional services
http://www.spatialys.com