Gtk_widget_measure cached results

[q962 (提及)]

Gtk 4.10.4

---

GIF

layout

MyFlowBox   GTK_ORIENTATION_HORIZONTAL
  - MyChild ::wfh GTK_ORIENTATION_VERTICAL

I need to record the sum of the heights of the children when flowbox distributes the width to a fixed number of children in an even manner

So when I measure the child’s height, I pass the child’s width value as for_size to measure

But measure always returns the same value. Because the result is cached.

During the investigation, I found the key code

gtk/gtksizerequestcache.c · 4.10.4 · GNOME / gtk · GitLab

I currently don’t understand what this code means

    if (cur->lower_for_size <= for_size &&
		  cur->upper_for_size >= for_size)

I don’t know how to fix it.

I tried calling gtk_widget_queue_allocate before the measure child, but it didn’t work

[q962 (提及)]

I’m not quite sure about the logic of GtkSizeRequestMode .

My understanding is as follows:
width-for-height: Indicates that the height will also change when the width changes, that is, the width will not be affected when the height changes
height-for-width: Indicates that the width will also change when the height changes, that is, the height will not be affected when the width changes

Can anyone describe it in more words?

[lb90]

Hi! The way I understand it is:

• width for height: GTK gives you the height of your control and you tell GTK what width the control needs
• height for width: same, but GTK gives you a width and you tell GTK the required height

For example, suppose your control shows an image but must retain the aspect ratio, say height = 5/4 width. Here’s how you could implement the measure vfunc:

static void
my_control_measure (GtkWidget *widget,
                    GtkOrientation orientation,
                    int for_size,
                    int *minimum,
                    int *natural,
                    int *minimum_baseline,
                    int *natural_baseline)
{
  switch (orientation)
    {
    case GTK_ORIENTATION_HORIZONTAL:
      /* Width for height: GTK has given us a height (reported
       * in for_size), let's determine an appropriate minimum /
       * natural width
       */
      *natural = *minimum = for_size * 0.8;
      break;
    case GTK_ORIENTATION_VERTICAL:
      /* Height for width: GTK has given us a width (reported
       * in for_size), let's determine an appropriate minimum /
       * natural height
       */
      *natural = *minimum = for_size * 1.25;
      break;
    }
}

[q962 (提及)]

thank you for the explanation.

What I get is the opposite result.

[lb90]

Have you considered using a layout manager like GtkBoxLayout? With that you don’t have to implement measure yourself. See Custom widgets in GTK 4 – Layout – GTK Development Blog

[q962 (提及)]

I need more possibilities, so I need to create layout

I found the problem, the reason is that the understanding of for_size is not deep

[q962 (提及)]

This is my first attempt at thinking about for_size layouts.

It’s a simple question of logic

static void lx_list_info_card_measure( GtkWidget*     widget,
                                       GtkOrientation orientation,
                                       int            for_size,
                                       int*           minimum,
                                       int*           natural,
                                       int*           minimum_baseline,
                                       int*           natural_baseline )
{
	_SELF( widget );

	int min = 0, nat = 0;

	if ( for_size > 0 ) {  // important !!!
		min = for_size;
		nat = for_size;
	}
	else {
		gtk_widget_measure( self->main_child, orientation, -1, &min, &nat, NULL, NULL );
        for_size = min;
	}

	lx_widget_measure_opt( GTK_ORIENTATION_VERTICAL, orientation, minimum, *minimum, min );
	lx_widget_measure_opt( GTK_ORIENTATION_VERTICAL, orientation, natural, *natural, nat );

	int mmin = min, mnat = nat;

	if ( orientation == GTK_ORIENTATION_HORIZONTAL )
		return;

	gtk_widget_measure( self->label_child, orientation, for_size, &min, &nat, NULL, NULL );
	lx_widget_measure_opt( GTK_ORIENTATION_VERTICAL, orientation, minimum, *minimum, min );
	lx_widget_measure_opt( GTK_ORIENTATION_VERTICAL, orientation, natural, *natural, nat );
}

When I measure the size of the child control, for_size is provided, but the child control doesn’t use it. causing it to use its own size every time. However for_size can be larger than its own size.

The result looks like it was cached. I saw the cache when I was troubleshooting, so I thought it was the result of the cache.