Adopt 13718: remove irrlicht gradients

[siliconsniffer]

This PR is related to #15826, see this discussion #6733 (comment).

Disclaimer: I have close to zero experience with irrlicht, this is a first hands-on experience for me.

To do/discuss

This PR is a Work in Progress. As far as I can tell the main concerns are:

• missing contrast, could be mitigated with different brightness
• harder to recognize separate buttons in groups of buttons
• main menu tab color
• harder to distinguish from text fields, needs to still look clickable
• addition of colors
• 9-slice

Screenshots

RE: removing the faux 3d stuff - let's keep that in.

#15826 (comment)

[SmallJoker]

This PR does generally the same as #13718.

My opinion on this topic is unchanged since #13718 (comment). An API or the use of 9-sliced images might be needed to cover most use-cases and personal preferences.

[appgurueu]

This PR does generally the same as #13718.

It looks like this PR addresses at least one major concern (contrast) which was brought up on the original PR by about four different people, and addressing more concerns is planned.

I prefer the current buttons. Others may prefer flat ones.

Most people seem to prefer flat ones (see e.g. the reactions on roller's PR).

A general solution would IMO be to use 9slice drawing for all buttons so that games and players could overwrite the textures (normal, hover, press) on demand.

The problem of button stylability is already pretty much solved as far as games are concerned. Try e.g. Mineclonia.

The question that remains is how default buttons, in the main menu, before the user has done any configuration, should look. The default should look appealing to most (first time) users, and currently it just doesn't.

People don't want to have to configure the GUI of an application to look okay. Some applications let you choose a theme, many don't. I don't think we should maintain multiple themes or a bunch of settings, or introduce something like a "mainmenu texture pack" or direct users to edit some files if they want the main menu to look okay.

It is on us to sensibly choose this default, like any other default, and this was, as far as I know, never done: We just inherited the Irrlicht default styles.

And I don't think the gradient is currently the best approximation of what people expect buttons to look like.

[Zughy]

Concerning the 3rd screen: the red X might work but I wouldn't make the Login button green (definitely not that green, but anyway it can be argued that register and login bear the same weight - so same colour)

[siliconsniffer]

Concerning the 3rd screen: the red X might work but I wouldn't make the Login button green (definitely not that green, but anyway it can be argued that register and login bear the same weight - so same colour)

Thanks for your feedback. Keep in mind that this was just an "experiment", I wouldn't merge it like that either.
The green background color was a personal note, since the "default action" i.e. pressing enter triggers the login (if there is a username of course) - but that's by no means necessary and I completely agree that the color isn't fitting really well.
The red button might need some adjustment though, maybe change it to a regular instead of an image_button?
A more subtle red would also be beneficial.

[siliconsniffer]

Although I was previously more on the "let's find a compromise" side of things, I totally agree with @appgurueu.
It's, in my opinion, not feasible to find a compromise for the few people that prefer the gradients without creating an overly complicated solution for something that is meant to be provisional anyway.

In my opinion, we should move forward with this with only minor (e.g., color or contrast) changes before stalling again.
Maybe this could go into the RC? If enough people are upset by the change we can still roll it back.
In the end, this choice is upsetting people either way, but as appgurueu said, it's on us to choose the default.