Text displayed axoverlay disappears between camera restarts

[brunoarine]

I'm using the axoverlay to display real-time info on the video stream. The application works --- bounding boxes are drawn via the bbox API, and text is rendered via axoverlay ---, but only as long as I don't touch the browser window. If I reload the the camera web page or resize the browser window, the previously rendered text disappears and is never redrawn.

Some extra info:

• My code is inspired by the "object detection with YOLO" example with the "axoverlay" example from this repo, so I follow a similar structure.
• I have set an adjustment callback function, just like the axoverlay example in this repo.
• I've also defined a select stream callback function that always return TRUE.
• My render callback function is working correctly, because I checked and the draw_text() function is called at every axoverlay_redraw() call. So I suspect the problem must have to do with Cairo somehow.

Any ideas what might be going on? I'm using a P1648LE camera with ARTPEC-8 chip.

[Cacsjep]

Are you sure you use stream select callback correctly ?

[Cacsjep]

Ok that strange I would assume that stream select should also be invoked because you would see the overlay there as well. Sounds like on access stream all overlay get checked but for any reason the callback is not invoked and therefore your overlay is lost in space. Sounds like a bug. Wich OS ?

[Cacsjep]

Just for reference did it happen also with axoverlay example ?

[brunoarine]

The camera is running on Axis OS 12.5.73.

Just for reference did it happen also with axoverlay example ?

That's a good question. I just tested it here and it works as expected, even after reloading the page several times in a row.

The only difference though that I could spot is that I'm not using a glib Loop (just a "while" loop that calls axoverlay_redraw() whenever there's a data update). Do you think that could be the culprit?

[Cacsjep]

@brunoarine oh yeah you need anywhere in your app a running g main loop because the gmain loop handle callbacks.

Sounds like you currently bypass the render callback, eg. not using it, because you wrote that you using a while loop where you call redraw.

[brunoarine]

Thanks for the patience @Cacsjep, I do appreciate your effort in helping me with that!

Sounds like you currently bypass the render callback, eg. not using it, because you wrote that you using a while loop where you call redraw.

I think I'm not following. When I start the application, the logs show that the render callback is being invoked when needed. Proof of that is the text being displayed and updated on the screen as it should. Not only the render callback is correctly invoked, but the text drawing functions as well. Here's how they are defined:

void render_overlay_cb(gpointer rendering_context,
                       gint id,
                       struct axoverlay_stream_data* stream,
                       enum axoverlay_position_type postype,
                       gfloat overlay_x,
                       gfloat overlay_y,
                       gint overlay_width,
                       gint overlay_height,
                       gpointer user_data) {
    /* Silence compiler warnings for unused parameters/arguments */
    (void)postype;
    (void)overlay_x;
    (void)overlay_y;
    (void)id;

    cairo_t* cairo_context = (cairo_t*)rendering_context;

    syslog(LOG_INFO, "Render callback engaged");
    syslog(LOG_INFO, "Overlay ID: %d", id);
    syslog(LOG_INFO, "Stream ID: %d", stream->id);
    syslog(LOG_INFO, "Render callback for camera: %i", stream->camera);
    syslog(LOG_INFO, "Render callback for overlay: %i x %i", overlay_width, overlay_height);
    syslog(LOG_INFO, "Render callback for stream: %i x %i", stream->width, stream->height);
    syslog(LOG_INFO, "Render callback for rotation: %i", stream->rotation);

    draw_text(cairo_context,
              48,
              48,
              *static_cast<OverlayData*>(user_data)->roi_intrusions,
              *static_cast<OverlayData*>(user_data)->line_crossings);
}

void draw_text(cairo_t* context,
               const gint pos_x,
               const gint pos_y,
               const long roi_intrusions,
               const long line_crossings) {

    syslog(LOG_INFO, "Cairo drawing function invoked!");

    cairo_save(context);
    cairo_text_extents_t te_length;
    gchar* str = nullptr;

    cairo_set_source_rgb(context, 1, 1, 1);
    cairo_select_font_face(context, "Sans", CAIRO_FONT_SLANT_NORMAL, CAIRO_FONT_WEIGHT_BOLD);
    cairo_set_font_size(context, 48);

    str = g_strdup_printf("ROI intrusions: %ld  Line Crossings: %ld", roi_intrusions, line_crossings);
    cairo_text_extents(context, str, &te_length);
    cairo_move_to(context, pos_x, pos_y);
    cairo_show_text(context, str);
    g_free(str);

    cairo_restore(context);
}

So I see "Cairo drawing function invoked!" and "Render callback engaged" at every update in the logs. The problem is that after I reload the video stream, the log messages keep on showing up, but there's no text overlay on the video at all.

[Cacsjep]

@brunoarine show the complete code where you call redraw ? And you need a running gmain loop. Without a running gmain loop some strange things could happen. Since the examples works, it's an issue with your code.

[Cacsjep]

Thanks for the patience @Cacsjep, I do appreciate your effort in helping me with that!

Sounds like you currently bypass the render callback, eg. not using it, because you wrote that you using a while loop where you call redraw.

I think I'm not following. When I start the application, the logs show that the render callback is being invoked when needed. Proof of that is the text being displayed and updated on the screen as it should. Not only the render callback is correctly invoked, but the text drawing functions as well. Here's how they are defined:

void render_overlay_cb(gpointer rendering_context,
                       gint id,
                       struct axoverlay_stream_data* stream,
                       enum axoverlay_position_type postype,
                       gfloat overlay_x,
                       gfloat overlay_y,
                       gint overlay_width,
                       gint overlay_height,
                       gpointer user_data) {
    /* Silence compiler warnings for unused parameters/arguments */
    (void)postype;
    (void)overlay_x;
    (void)overlay_y;
    (void)id;

    cairo_t* cairo_context = (cairo_t*)rendering_context;

    syslog(LOG_INFO, "Render callback engaged");
    syslog(LOG_INFO, "Overlay ID: %d", id);
    syslog(LOG_INFO, "Stream ID: %d", stream->id);
    syslog(LOG_INFO, "Render callback for camera: %i", stream->camera);
    syslog(LOG_INFO, "Render callback for overlay: %i x %i", overlay_width, overlay_height);
    syslog(LOG_INFO, "Render callback for stream: %i x %i", stream->width, stream->height);
    syslog(LOG_INFO, "Render callback for rotation: %i", stream->rotation);

    draw_text(cairo_context,
              48,
              48,
              *static_cast<OverlayData*>(user_data)->roi_intrusions,
              *static_cast<OverlayData*>(user_data)->line_crossings);
}

void draw_text(cairo_t* context,
               const gint pos_x,
               const gint pos_y,
               const long roi_intrusions,
               const long line_crossings) {

    syslog(LOG_INFO, "Cairo drawing function invoked!");

    cairo_save(context);
    cairo_text_extents_t te_length;
    gchar* str = nullptr;

    cairo_set_source_rgb(context, 1, 1, 1);
    cairo_select_font_face(context, "Sans", CAIRO_FONT_SLANT_NORMAL, CAIRO_FONT_WEIGHT_BOLD);
    cairo_set_font_size(context, 48);

    str = g_strdup_printf("ROI intrusions: %ld  Line Crossings: %ld", roi_intrusions, line_crossings);
    cairo_text_extents(context, str, &te_length);
    cairo_move_to(context, pos_x, pos_y);
    cairo_show_text(context, str);
    g_free(str);

    cairo_restore(context);
}

So I see "Cairo drawing function invoked!" and "Render callback engaged" at every update in the logs. The problem is that after I reload the video stream, the log messages keep on showing up, but there's no text overlay on the video at all.

Sorry I misunderstood something, I had understand that you call the draw functions without the callback

[brunoarine]

@Cacsjep I decided to implement your suggestion and replace the while loop with glib's loop and voilà, the axoverlay API started working as it should, even after dozens of page reloads. I couldn't believe my own eyes. That was a happy closure to a one-week brain scraping :D

Again, thank you so much for all the patience and have a good weekend!