How to draw a focus indictor on a drawing area

Platform
1

Hello everyone,

I have a custom widget (an image viewer implemented as a GtkDrawingArea subclass) which has some keyboard bindings, so I need a focus indicator.

What’s the best way to do this? Should I use GtkOverlay to float some other widget over my drawing area and rely on that to draw the indicator? What would be the best widget to float on top?

2

Hi,

gtk3 or gtk4?
Do you want the focus indicator on the whole DrawingArea, or on a smaller element?

3

Hi @gwllems,

Sorry, gtk4, I should have said.

My image viewer looks like this:

image
image1128×1029 130 KB

So I’m currently drawing the focus indicator as a thin line just inside the window in my _snapshot() handler. It’d be much better if I could get gtk to draw it for me, of course!

4

OK, then the easiest way IMHO is to use a custom CSS:

drawingarea:focus {
	outline-color: @theme_selected_bg_color;
	outline-offset: -3px;
	outline-width: 2px;
	outline-style: dotted;
}
5

Note that for testing, you can launch the gtk inspector with CtrlShiftI and paste the style above in the “CSS” tab.
That’s an easy way to visualize the outcome.

6

Sorry for the very late reply, it took me ages to get CSS drawing anything on my widget (the trick was to call gtk_widget_class_set_css_name(widget_class, "imagedisplay") in my class init, ooops).

I ended up with:

imagedisplay {
  transition: outline-offset 200ms cubic-bezier(0.25, 0.46, 0.45, 0.94);
  border-radius: 7px;
  outline: 2px solid transparent;
  outline-offset: 4px;
}

imagedisplay:focus {
  outline-color: @theme_selected_bg_color;
  outline-offset: -3px;
}

Which kind-a looks a bit like the gtk focus indicator, but it won’t fade away after a while in the way that (for example) the focus ring on the scale widget will.

1 Like
7

I think you need :focus:focus-visible instead of just :focus for this.

8

I tried that, but it stopped it working completely :frowning:

Do you know if there’s something I need to call to make my GtkDrawingArea use the focus-visible state? I looked through the gtkscale sources but nothing jumped out at me (probably being dumb).

9

Weird, that works on my side…

Have you used this?

imagedisplay:focus:focus-visible {
  outline-color: @theme_selected_bg_color;
  outline-offset: -3px;
}

Make sure there are no spaces around the :, that will change the meaning.

10

Ah! I was testing it by clicking in the drawing area, but nothing happens then. It DOES appear if I tab the focus in and out of the drawingarea, and it does vanish after a few seconds.

Thank you! That was quite a journey.

1 Like
11

My final solution:

imagedisplay {
  transition-property: outline-offset, outline-color;
  transition-duration: 300ms;
  animation-timing-function: ease-in-out;
  border-radius: 7px;
  outline-offset: 4px;
  outline: 2px solid transparent;
} 

imagedisplay:focus:focus-visible {
  outline-offset: -3px;
  outline-color: @theme_selected_bg_color;
}

Ideally I’d be able to get $focus_border_color for a better match with the rest of gtk, but I think that’s not part of the set of public colors.

1 Like
12

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