layer should not get the "show" checkbox disabled based on visiblity slider state

[aseerel4c26]

Michael, while you're at it: The automatic "hide" feature of a layer is breaking my GUI expectations (which is most striking if you use the new mouse wheel slider movement - ticket #13703 ).

Steps:

1. scroll muuuuch to lower the Opacity of a layer until the slider is at the lowest position
2. (the layer automatically gets the "show" checkbox disabled)
3. scroll in the opposite direction to increase the Opacity again (undo your action in 1.)

Expected: layer gets visible again since you have undone your movement
Actual: the layer stays inactive and you need to check the box (which you've never enabled)

I guess it is this bit (and could not find a comment why it is there) (source):

if (getRealValue() <= 0.001 && !getValueIsAdjusting()) {
	                setVisibleFlag(false);

Is there a reason for this feature? I would suggest to not automatically disable the "show" checkbox based on slider action. Thank you! :)

[michael2402]

The feature is there because of historical reasons. The visible boolean flag was there first, the slider came afterwards.

I don't even think that the visible flag is required any more. We could remove it and define a layer to be visible if it's visibility is not 0. The main reason I see is the visibility toggle button: It needs to know the old opacity.

The problem is that users may not really know what happens if they set the visibility to 0 - the layer is still marked as visible but they don't see anything.

[aseerel4c26]

Thanks for the explanation.

I do not think that "users may not really know ..." is a problem. The user is using the slider actively to lower the opacity, so it should be obvious what the slider does. By the way: even with the current setup users "users may not really know ..." why a layer is not visible despite the "show" checkbox being ticked: imagine the user setting a opacity of 0.05. That's not really visible, but the "show" checkbox may still be enabled.

In addition: Currently I see the "visible" control at two places. The eye symbol in the layers and the checkbox in the visibility control popup. I do not think that we need an additional checkbox there.

Maybe someone else could share their thoughts!