Simplify CTabFolderRenderer to use flat tabs

[vogella]

@HeikoKlare suggested that CTabFolderRenderer should use flat tabs instead of rounded ones (which IMHO look really bad).

@HeikoKlare please approve so that can I start working on this. This will be a visible change for SWT UIs but I think most users will welcome it and IMHO we are allowed to improve our L&F.

[HeikoKlare]

I am in favor of simplifying the SWT implementation of the CTabFolder rendering via CTabFolderRenderer in addition to the simplification of the CSS-based rendering in Platform UI.

I think we have discussed in a community call with @azoitl last year that we should maybe have a deprecation period for such a change (also for the one in Platform UI). But since it's not a breaking change (in the sense that an application may not start/work anymore) we could also skip that for the sake of faster progress. Having such a simplification pending for two years seems inappropriate given the fast moving world 🙂

Alois also mentioned that removing the rounded tabs in CTabFolderRenderer would be beneficial for moving forward here:
eclipse-platform/eclipse.platform.ui#3806 (comment)

[azoitl]

Just one word of caution. Event tough the rounded edges are not API CTabRendering in Platform UI is partly using this and even access some values via reflection. So when we move forward here which I would strongly support I think cleaning CTabRendering first and then moving to CTabFolderRender would be the better approach.

[vogella]

@azoitl I think the following fields are accessed via reflection and I don't think they are related to rounded corners.

• selectionGradientVertical
• gradientVertical
• selectionGradientColors
• selectionGradientPercents
• gradientColors
• gradientPercents

[azoitl]

Interesting I was pretty sure when we did the analysis for starting the work on the vertical tab folders there was something. But also the history is rather clear.

[HeikoKlare]

I have to admit that I am always a bit confused about the different types of rounded tabs and how to configure them, so maybe some of the confusion is caused by that and we should clean that up. As far as I know, we have three shapes of tab header:

1. Plain/rectangular tab header: those are the ones we have as default in the CSS based rendering now/soon. As far as I know, those are only supported by the CSS-based renderer and not by SWT's CTabFolderRenderer (but I would be in favor of making SWT default to that as well):
   
2. Simple round tab header: those are the ones that we enabled in the CSS-based renderer when using the "Use rounded tabs" preference and are similar/equal to the default tab header when using SWT's CTabFolderRenderer:
   
3. Curved round tab headers: those are the ones that were used by the "Classic" theme and are provided by SWT's CTabFolderRenderer via setting the simple property of the CTabFolder' to false:
   

So there might be some confusion about which kind of "round" we are talking about. I am also not sure how the curved round tab header are realized when using the "Classic" theme, i.e., if there is an implementation for that in the CSS-based CTabRendering or if that theme uses the CTabFolderRenderer capability.

[vogella]

The flatten look in platform ui is a tab renderer registered via CSS. Example

.MPartStack {
font-family: '#org-eclipse-ui-workbench-TAB_TEXT_FONT';
swt-tab-renderer: url('bundleclass://org.eclipse.e4.ui.workbench.renderers.swt/org.eclipse.e4.ui.workbench.renderers.swt.CTabRendering');
}

[BeckerWdf]

3. Curved round tab headers

Aren't we talking about removing these in the Lars' PR?

[HeikoKlare]

Aren't we talking about removing these in the Lars' PR?

That PR (eclipse-platform/eclipse.platform.ui#3822) removes the simple round tabs, not the curved ones. The "Use round tabs" preference is for those simple round tabs. And the curved ones will still be available with the "Classic" theme and thus even after Lars' PR:

It's configurable via CSS property "swt-simple". Here is the according handler that sets the CTabFolder's simple property: https://github.com/eclipse-platform/eclipse.platform.ui/blob/master/bundles/org.eclipse.e4.ui.css.swt/src/org/eclipse/e4/ui/css/swt/properties/custom/CSSPropertySimpleSWTHandler.java

[BeckerWdf]

Aren't we talking about removing these in the Lars' PR?

That PR (eclipse-platform/eclipse.platform.ui#3822) removes the simple round tabs, not the curved ones. The "Use round tabs" preference is for those simple round tabs. And the curved ones will still be available with the "Classic" theme and thus even after Lars' PR:

It's configurable via CSS property "swt-simple". Here is the according handler that sets the CTabFolder's simple property: https://github.com/eclipse-platform/eclipse.platform.ui/blob/master/bundles/org.eclipse.e4.ui.css.swt/src/org/eclipse/e4/ui/css/swt/properties/custom/CSSPropertySimpleSWTHandler.java

Ah. Then I did missunderstood this. Anyway I am fine with this...

[vogella]

@HeikoKlare what should be do about? I suggest to remove the drawing logic, mark the API as deprecated and for removal and make it a no-op for now. That way we would benefit from cleaned API and remove a drawing logic which looks broken.

[HeikoKlare]

I suggest to remove the drawing logic, mark the API as deprecated and for removal and make it a no-op for now. That way we would benefit from cleaned API and remove a drawing logic which looks broken.

I would be totally fine with that. I am just not sure if everyone will be happy if that styling is removed, but we of course do not have to make everyone happy. @BeckerWdf wdyt?
What do we do with the "Classic" theme then? If I am not mistaken, there will only be slightly different colors (compared to Light theme) remaining, but the essential difference (the tab style) will be gone. Should we maybe mark that as "depracated for removal" as well and add some "(deprecated)" suffix to the theme name or the like?

If we agree to remove that style, it would probably be good to do for M1 (i.e., this week), so that at least those people using milestone builds will notice (in case they use "Classic" theme) and can complain a while before the next release.