about this:

> is there any way to create callbacks from the javascript world using the
Webkit2Gtk webview?

I've created a JSON communication channel between GJS and the WebView
through title notifications:


The nitty-gritty is that you change your title from the page

document.title = `${SECRET}:js=${JSON.stringify(data)}`;

and you intercept it from GJS side

webView.connect('notify::title', (self, params) => {
  if (`${SECRET}`:js=/.test(self.title)) {
    const data = JSON.parse(self.title.slice(SECRET.length + 4));
    // do stuff ... then ...
    const response = {};
        new CustomEvent(
          {detail: ${JSON.stringify(response)}}
      (self, result, error) => {

This way you can pass any serializable data to the listener and send
eventually data back. The SECRET can be any channel, for circular data just
use one of the many circular JSON parsers/stringifiers (i.e. flatted or

Hope this helps at least with the last part of the question.

P.S. on DOM, a table with 1.000.000 rows would be slow as well, the way I'm
scaling these kind of tables on DOM is by rendering only what's visible
(fixed rows height helps a lot with this) virtually updating the scroll bar
which is **not** the native one or performance will be super bad regardless.

On Mon, Oct 8, 2018 at 12:44 PM ente <e...@ck76.de> wrote:

> Hi,
> I am facing performance issues in GTK upon presenting a big amount of
> tabular data. First I used GtkListbox for it's layout flexibility. Handling
> more than 10,000 items gets inacceptable slow. Switching to GtkTreeview I
> can handle some 300,000 items after applying a few optimizations (column
> sizing fixed, fixed height mode): a full load takes about 4 seconds, i.e.
> the application feels anything but "responsive" although this is ... ok.
> Currently I see 2 options: dropping Gtk in favor of a HTML frontend (that
> feels awkward to say) or implementing paging on the GtkTreeview.
> At this moment I am analyzing the reasons for the performance issues. I
> measured the time it takes to generate a number of labels in a simple loop
> (no call ot GtkMain) and to add those labels to a GtkBox:
> * 100 labels in 1.7 ms
> * 1,000 labels in 20.9 ms
> * 10,000 labels in 610 ms
> * 100,000 labels in 1m18s
> After the loop I pack the GtkBox into a window and show it. That takes
> another century to show up.
> If I adjust the loop to skip the packing of the labels into the box, the
> times are down to:
> * 10,000 labels in 115 ms
> * 100,000 labels in 940ms
> The windows shows up instantly (although empty of course).
> So my performance issue is related to the packing. In my tests with the
> GtkTreeview it seems speficially to boil down to the sizing and signalling
> of the items: The performance of the treeview was highly impacted by the
> fixed height mode & the fixed column sizing (more than ordering by a column
> or calling GtkMain while adding rows). So my question goes down to: How can
> I further optimize my way of using GTK in order to speed up UI? Is there
> any way to add 1,000,000 labels to a GtkBox in less than a second? Could I
> somehow suspend the signalling during UI creation and replace it by a "I am
> done, now calculate all the sizes" signal? Am I wrong about my assumption
> that the sizing signalling is the cause for the low performance?
> With regards to the treeview: After initially creating the data rows I am
> calculating values that affect 4 columns out of 10 columns. So far I
> determine the GtkTreeIter of the affected row and update all cells in that
> row using gtk_list_store_set. Should I adjust to update the affected
> columns only? When I implement paging for the TreeView: should I rather
> drop the existing ListStore and create a new or is it faster to overwrite
> all elements in the Liststore with the new items?
> I tried to use the GtkBuilder in order to setup a box with 100,000 labels.
> This performance was somewhat the same as creating the labels in a loop (I
> didn't keep the measurements).
> I could isolate the problem to UI rendering. If I don't assign my
> ListStore to the Treeview, all is fine. As soon as my ListStore is filled,
> I assign the model to the treeview. That's the most time consuming step.
> Last question: is there any way to create callbacks from the javascript
> world using the Webkit2Gtk webview? More specificly: I am working in go
> language. I am aware of the webview widget. Unfortunately that's a window.
> I would prefer to rather place a widget into a native GtkApplicationWindow.
> Using Eval I can inject anything into the DOM. How do I get events from the
> DOM back to go?
> Background on the application:
> I am developing a text analysis application. Text fragments get
> precalculated attributes assigned. Based on these attributes and the
> Levensthein distance between fragments, someone is supposed to (for now:
> manually) define text fragment categories (categories). Roughly speaking
> the application has a paned window: on the left I show the category list or
> an editor for a new / existing category; on the right I show a list of text
> fragments with the major 3 attributes or a details view on a specific
> fragment: all attributes and a list of similar fragments.
> The smallest amount of text fragments to be analyzed and categorized is
> about 300,000 items. The number of items goes easily up to 5,000,000 or
> even much more. Categorizing all fragments requires about 100 to at maximum
> 1,000 categories, i.e. there is quite some clustering among those text
> fragments. On the interface I work with highlight colors: a human can
> easily realize which fragements are already clustered and which aren't.
> Usually only a small number of text fragment categories are of special
> interest. One could compare it to a log file: I don't care so much about
> how often someone sucessfully authorized; it is much more interesting if
> someone suddenly fails to authorize.
> thanx,
> ente
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