Allow disabling elements; add :focused and :disabled states

[v-rob]

This PR allows formspec elements to be disabled with set_disabled[<name 1>,<name 2>,...] and styled with the :focused (last interacted with element) and :disabled style selectors.

Nearly all interactive elements can be disabled, with the effect of graying out the text for most of them (it all depends on what Irrlicht decides to do). Disabled buttons, by default, have gray text and a content_offset of 0 when pressed. The default button border also does not indent in the pressed state when disabled. This cannot be changed, but I doubt anyone would want such behaviour on a disabled button anyway.

The :focused selector takes lower precedence than everything except :default whereas :disabled takes highest precedence.

This screenshot shows all the features. The right elements are disabled elements, whereas the left are enabled. The bottom two buttons use the :focused and :disabled selectors combined with other selectors.

To do

This PR is Ready for Review.

How to test

Make sure disabled elements don't interact at all, especially buttons; check that selectors work properly, including combination. The above screenshot:

formspec_version[4]
size[9,13]

set_disabled[checkbox-2,button-2,image_button-2,item_image_button-2,table-2,textlist-2,dropdown-2,field-2,pwdfield-2,textarea-2,scrollbar-2,tabheader-2]

checkbox[1,0.5;checkbox-1;checkbox-1]
button[1,1;3,0.7;button-1;button-1]
image_button[1,2;3,0.7;air.png;image_button-1;image_button-1]
item_image_button[1,3;3,0.7;air;item_image_button-1;item_image_button-1]
table[1,4;3,0.7;table-1;table-1,-;1]
textlist[1,5;3,0.7;textlist-1;textlist-1,-;0]
dropdown[1,6;3,0.7;dropdown-1;dropdown-1,-;0]
field[1,7;3,0.7;field-1;field-1;field-1]
pwdfield[1,8;3,0.7;pwdfield-1;pwdfield-1]
textarea[1,9;3,0.7;textarea-1;textarea-1;textarea-1]
scrollbar[1,10;3,0.7;;scrollbar-1;scrollbar-1;0]
tabheader[1,11.7;3,0.7;tabheader-1;tabheader-1,-,-;1;;]

checkbox[5,0.5;checkbox-2;checkbox-2]
button[5,1;3,0.7;button-2;button-2]
image_button[5,2;3,0.7;air.png;image_button-2;image_button-2]
item_image_button[5,3;3,0.7;air;item_image_button-2;item_image_button-2]
table[5,4;3,0.7;table-2;table-2,-;1]
textlist[5,5;3,0.7;textlist-2;textlist-2,-;0]
dropdown[5,6;3,0.7;dropdown-2;dropdown-2,-;1]
field[5,7;3,0.7;field-2;field-2;field-2]
pwdfield[5,8;3,0.7;pwdfield-2;pwdfield-2]
textarea[5,9;3,0.7;textarea-2;textarea-2;textarea-2]
scrollbar[5,10;3,0.7;;scrollbar-2;scrollbar-2;0]
tabheader[5,11.7;3,0.7;tabheader-2;tabheader-2,-,-;1;;]
				
style_type[button:default;bgcolor=gray]

style_type[button:focused;bgcolor=red]
style_type[button:focused+hovered;bgcolor=orange]
style_type[button:focused+pressed;bgcolor=yellow]
set_focus[focus-style;true]
button[1,12;3,0.7;focus-style;Focused Styling]

style_type[button:disabled;bgcolor=green]
style_type[button:disabled+focused;bgcolor=violet]
style_type[button:disabled+hovered;bgcolor=cyan]
style_type[button:disabled+pressed;bgcolor=blue]
set_disabled[disable-style]
button[5,12;3,0.7;disable-style;Disabled Styling]

[Zughy]

Great job as always :)
A few suggestions:

• greying out item buttons and item image buttons. I mean the image, not just the text
• greying out tables, tabheaders and textlists text too to make it consistent
• greying out the background of fields, textareas and pwdfields

[v-rob]

Sorry, but these aren't very feasible just yet:

1. I'd rather not try image modifiers yet until/if we have an image modification property; otherwise, the image will be forced to be gray without any way for mods to change it. Better to let the mods desaturate it themselves for now (^[colorize might work).
2. tabheaders don't have an setOverrideColor property, and I can't add it without absorbing it's entire code. tables have tableoptions which is certain to interfere with style, so I don't want to touch it either for now.
3. Sorry, can't change the background color for these either. Irrlicht doesn't support it.

None of these are final. It's just that Irrlicht limitations don't make these possible on a short-term basis, so this PR in particular won't add them. Later, when we do styling revamps on other elements, these features will almost certainly be added.

[appgurueu]

If I get you right, you are using focused as "not disabled" ?

I consider this to be misleading. Focused means the element is basically the "last selected element". The opposite of disabled is enabled

[v-rob]

No, :focused is the last selected element, like you think it should be, and like CSS :focus. Was I unclear somewhere?

Also, forgot to mention, but (pwd)fields and textareas now have gray text when disabled by default.

[appgurueu]

No, :focused is the last selected element, like you think it should be, and like CSS :focus. Was I unclear somewhere?

Also, forgot to mention, but (pwd)fields and textareas now have gray text when disabled by default.

Sorry for the misunderstanding.

[v-rob]

Closing all my inactive formspec PRs. There's little interest in them as of now and the formspec replacement is making fair progress, and I want to avoid causing more problems like #10083 due to my interests being divided between the replacement and extra features on the current system. If anyone really thinks that any of these are essential and gives a good reason why it really can't wait for the replacement (better than saying that one mod needs it), I'll reopen.

I know an argument might be put forth that there's no knowing when the formspec replacement will come out, but I really think that it will become a reality, although maybe not soon. I might not display my progress prominently, but it's moving along at a steady rate.

[kilbith]

Formspecs will not be replaced anytime soon by modders, man.

[v-rob]

True, but that doesn't mean that we have to keep adding features to them forever. As I said, I'll reopen them if there's enough interest, meaning multiple mods need it. ATM, I'm trying to focus my work without a lot of sidetracking (and get the PR count down a little). For instance, I left #8679 open because multiple people expressed how useful it would be, while the others I closed had no such modder support.