Draft: Move the FlApplication from the template into the linux embedder.

[jane400]

This introduces the class FlApplication, which handles the passing of command line arguments into dart and bringup of a GtkWindow embedding the FlView with for e.g. desktop specifc quirks.

Changes:

This now allows the flutter linux template to be more simple:

#include <flutter_linux/flutter_linux.h>

#include "flutter/generated_plugin_registrant.h"

void view_constructed(FlApplication* app, GtkWindow* window, FlView* view, gpointer user_data) {
  fl_register_plugins(FL_PLUGIN_REGISTRY(view));

  gtk_window_set_title(window, "{{projectName}}");
  gtk_window_set_default_size(window, 1280, 720);
  gtk_widget_show(GTK_WIDGET(window));
}


int main(int argc, char** argv) {
  g_autoptr(FlApplication) app = fl_application_new(APPLICATION_ID, G_APPLICATION_NON_UNIQUE);
  fl_application_connect_view_constructed (app, view_constructed, nullptr);
  return g_application_run(G_APPLICATION(app), argc, argv);
}

I think this is a pretty API, which should be forward compatible with multi view/window flutter applications. Suggestions welcome! :)

I would like to also include titlebar changes in this PR. My plan is to listen for the env variable XDG_CURRENT_DESKTOP equals GNOME instead of assuming GNOME implicitly with use_headerbar = TRUE on all wayland platforms. Should I include this here or make a new PR?

List which issues are fixed by this PR. You must list at least one issue. https://github.com/flutter/flutter/issues/142920

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Pre-launch Checklist

I didn't run the testsuite yet, and this probably needs new tests (unless someone tells me otherwise :) ). Will have to look into that. Not all clang-format suggestion are applied, as I disliked some of them. (I'm coming from a GObject dev background and tried to keep some GObject style as outlined in the linux-embedder Exception)

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[cbracken]

/cc @robert-ancell for thoughts.

@jane400 is this still something you're looking into? If so, unfortunately policy requires a signed CLA from contributors as mentioned in the bot reply above. Info in the failed invocation link above.

[jane400]

The CLA check shouldn't fail with the next reinvocation/update of the MR.

I saw during the creation of this MR, that there were multiple MRs introducing Multi View support into flutter, hence put this MR in my backlog.

I would like to also include titlebar changes in this PR. My plan is to listen for the env variable XDG_CURRENT_DESKTOP equals GNOME instead of assuming GNOME implicitly with use_headerbar = TRUE on all wayland platforms. Should I include this here or make a new PR?

Also waiting for an opinion for this.

[jane400]

I got a chance to actually read the Multi-view runner APIs design documents.

Regarding:

static void activate_cb(FlApplication* app, gpointer user_data) {
  fl_register_plugins(FL_PLUGIN_REGISTRY(fl_application_get_view()));

  GtkWindow* window = fl_application_get_window(app);
  gtk_window_set_title(window, "{{projectName}}");
  gtk_window_set_default_size(window, 1280, 720);
}

We could go for this, but fl_application_get_view and fl_application_get_window might be confusing with FlApplication supporting multi view windows, it should rather be called fl_application_get_initial_view (which may be null).

I would still rather provide a custom signal, where we give the initial view to the user. Especially as g_application_activate can be called multiple times with certain G_APPLICATION_FLAGS.

But one could also make the case that FlApplication should constrain itself to a single window, then this API is perfectly fine, and multi-view users should just use GApplication directly and override ->activate

[robert-ancell]

I've been thinking about this in regards to multi-window and also delaying the view until the first frame is shown (https://github.com/flutter/flutter/issues/151098). It's clear we want FlApplication to handle all this for most Flutter applications rather than making the template more complicated. I propose this PR is simplified to just do the current behaviour of the template, and then we build from that (as noted in the review comments). @jane400 are you happy to update this PR to that? Thanks.