[Qgis-developer] standardisation of the editing map tools: modify behaviour of press-pan-release tools

[Denis Rouzaud]

Hi all,

There is somehow an inconsistency in the behaviour of the current 
editing map tools.

Some, like add features, uses the left click to trigger the action.
Others, like the node tool or move feature use press-pan-release mouse 
events:
* mouse press to select the node/feature
* mouse mouse to move it
* mouse release sets the position.

I would propose to standardise this and for the latter tools propose the 
following work flow:
* left click enables the move
* left click again to validate at position
* or right click to cancel

Why changing this?

If you look at CAD software, they also use the proposed approach. And 
there's a reason for doing so, which is valid for QGIS too.

We are looking at improving the CAD tools in QGIS. In this area, I 
recommend trying the fantastic CADinput plugin made by Olivier Dalang. 
The plugin works on top of any map tool and enables CAD tools for each 
of them.

The problem with the press-pan-release map tools is that you can't truly 
interact while you are actually in the action of the map tool (holding 
the click):
* you can't click anymore and this prevents from using intermediate 
points (you have to use the tool several times and repeat the operation 
as many times as intermediate points you need)
* it is not really user friendly to have to press keys while holing the 
click

This is why, changing the map tools behaviour is requested if we want to 
go further with CAD tools in QGIS.

Regarding the future of CAD tools in QGIS, I am quite sure the plugin 
proposed by Olivier would be a good way to go for QGIS, but it still 
might be a bit early to integrate it in core. The idea is rather first 
to extend the API and propose ready to use methods, so it will be easy 
to implement your preferred solution in a plugin.

But first, we need to standardise the map tools.

So, the bottom line, any objection to changing the behaviour of:
* edit node tool
* move feature
* rotate feature
* move label
* rotate label
* any other press-pan-release map tool that I am not aware of
???

Best wishes,

Denis