Light tool disable click

[ericmehl]

Previously we were making the light position tool disabled and invisible if anything except a light is selected. This still allowed clicking and dragging, so users could still move a non-light object, which is not our intention.

I also changed the behavior when pressing the V / Shift + V key when the handle is visible but disabled (for example if more than one light is selected). Previously the pointer would change when pressing V, but you couldn't actually set the target since the tool is disabled. Now it won't change the pointer so the user won't expect an action when none is possible.

Checklist

• I have read the contribution guidelines.
• I have updated the documentation, if applicable.
• I have tested my change(s) in the test suite, and added new test cases where necessary.
• My code follows the Gaffer project's prevailing coding style and conventions.

[johnhaddon]

Summary of discussion from yesterday : we want to steal V + click even when we're not using it, and we want to display an ISO 7010 - P001 pointer to explain that the action is prohibited.

[ericmehl]

we want to steal V + click even when we're not using it, and we want to display an ISO 7010 - P001 pointer to explain that the action is prohibited.

Those changes are done via a couple of dropped commits and ffa7ad1

I think the last detail is taken care of in ace2675. The notEditable pointer was getting left on when hovering over a handle that is editable. For example :

1. Create a light and select it
2. Activate light placement tool
3. Change the mode to highlight
4. Place the light with V + click to get a distance handle
5. Hold Shift + V to set pivot placement, which is not compatible with highlight mode, so you get the notEditable icon
6. Hover over the distance handle or rotate handle. These are editable, so the cursor should reflect that, and also go back to notEditable when you move away from the tool

[johnhaddon]

Thanks Eric, LGTM. I've rebased and retargeted this to 1.4_maintenance and at the same time taken the liberty of using distanceHandle()->getRequiresPivot() in updatePointer(), rather than checking Mode - this aligns the check with the ones we're performing elsewhere. Merging...