add support for specifying text alignment on selectables

[haldean]

Adds an optional parameter to Selectable that allows clients to specify the text alignment within the Selectable, and adds a section in the demo to demonstrate text alignment support:

In terms of implementation, this is extremely simple: Selectable was already calling an API that supports text alignment, but had hard-coded it to top-left. This adds a text_align parameter on the Selectable function and just passes that straight through to RenderTextClipped instead of the hard-coded (0, 0). Backwards-compatibility is preserved by defaulting the text_align parameter to (0, 0), i.e., top-left.

A video of the demo in action:

Works on #1260

[ocornut]

Hello @haldean,

Could you clarify what are you using this for?
Do you typically always use the same alignment?

My intuition is we ought to avoid adding too many rarely used parameters to function, and this could be a better fit as a style variable. See style.ButtonTextAlign/ImGuiStyleVar_ButtonTextAlign ?

[haldean]

I am using it in a couple places in my UI; one in which I want the text to be properly centered (for a UI not unlike the one in the demo, I have a grid of selectables I want to turn on and off), and everywhere else I want it to be center-left (I have a bunch of places where I manually set the height to be larger to make it a bigger click target, and I want the text to be vertically centered in the taller box).

I'll make the change to be a style variable; using PushStyleVar for my grid UI makes sense, because it's kind of an odd thing anyway. I was just going off of what was said in #1260 on this, but I actually think the style variable makes more sense.

[ocornut]

Thank you, that would be perfect!

For the names in the demo, I would suggest using snprintf to generate a string.

I am wondering if it would make sense changing the default from (0.0f,0.0f) to (0.0f,0.5f) ?

[haldean]

I think (0, 0.5) is a nicer default but I also was exercising some caution around changing the current behavior; if you are OK with changing behavior to have a nicer default that sounds good to me!

[ocornut]

I don't know yet to be honest. Left-align is pretty much a required default to keep, and center-left align can look a little odder than embracing upper-left?

You can do the PR with (0.0f,0.0f) and it'll be easy to change soon or later if if deem it viable.

[haldean]

Yeah, I just tested with (0, 0.5) and actually a number of things draw poorly; menus in particular end up looking strange. I think keeping the default at (0, 0) is the way to go for now

[ocornut]

I think the RenderTextClipped() calls needs to be changed to use:

RenderTextClipped(bb_inner.Min, bb_inner.Max, ...., align, &bb);

Passing an different clipping rectangle from the inner rectangle.
This will probably fix what you saw on the menu.

Otherwise alignment will be incorrect (more noticeable if you increase style.FramePadding).

[haldean]

all of these had to change because SelectableTextAlign was too long for the comment to be aligned properly

[haldean]

You're right, that fixed it. I still left the default at (0, 0). It's a style variable now, and I updated the demo and added the appropriate sliders to the style editor. Let me know if there's any more changes you would like to see!

[ocornut]

Thanks, I'll merge it shortly!

[ocornut]

Merged now, thank you Haldean !