Misc questions regarding the axoverlay example

[apljungquist]

It would be great if anyone could help me answer any or all of these questions. For context I'm trying to write Rust bindings for the API, which is why I'm extra interested in how it works in general as opposed to does my current app do what I expect.

1

It looks to me like the errors would pile up if axoverlay_destroy_overlay fails in this snippet, which from my understanding of the docs is a bug. Is this a mistake in the app or does the API follow some other convention?

    axoverlay_redraw(&error);
    if (error != NULL) {
        syslog(LOG_ERR, "Failed to draw overlays: %s", error->message);
        axoverlay_destroy_overlay(overlay_id, &error);
        axoverlay_destroy_overlay(overlay_id_text, &error_text);
        axoverlay_cleanup();
        g_error_free(error);
        g_error_free(error_text);
        return 1;
    }

acap-native-sdk-examples/axoverlay/app/axoverlay.c

Line 446 in 33b7742

axoverlay_destroy_overlay(overlay_id, &error);

https://docs.gtk.org/glib/error-reporting.html#rules-for-use-of-gerror

2

Should this be read to imply that the default value is something other than NULL?

struct axoverlay_settings settings;
    axoverlay_init_axoverlay_settings(&settings);
    settings.render_callback     = render_overlay_cb;
    settings.adjustment_callback = adjustment_cb;
    settings.select_callback     = NULL;

acap-native-sdk-examples/axoverlay/app/axoverlay.c

Line 383 in 33b7742

settings.select_callback = NULL;

axoverlay_init_axoverlay_settings
Initializes an axoverlay_settings struct with default values;

https://axiscommunications.github.io/acap-documentation/3.5/api/axoverlay/html/axoverlay_8h.html#a3564acf79f48af97e2414127696f82d7

3

The docs state that

axoverlay_init ... must be called before any other axoverlay function

https://axiscommunications.github.io/acap-documentation/3.5/api/axoverlay/html/axoverlay_8h.html#abcee514e8d556934e857fd594a471865

This seems to contradict the example where axoverlay_is_backend_supported is called first:

if (!axoverlay_is_backend_supported(AXOVERLAY_CAIRO_IMAGE_BACKEND)) {
      syslog(LOG_ERR, "AXOVERLAY_CAIRO_IMAGE_BACKEND is not supported");
      return 1;
  }

  //  Initialize the library
  struct axoverlay_settings settings;
  axoverlay_init_axoverlay_settings(&settings);
  settings.render_callback     = render_overlay_cb;
  settings.adjustment_callback = adjustment_cb;
  settings.select_callback     = NULL;
  settings.backend             = AXOVERLAY_CAIRO_IMAGE_BACKEND;
  axoverlay_init(&settings, &error);

Am I correct in assuming that this function is exempted?
If so, are there any other exempted functions (apart from the setters that explicitly say they must be called before axoverlay_init)?