gtkui: Hide info area text containing emoji properly. Closes: #1491

[radioactiveman]

Fading out text with emoji characters can lead to them still being displayed above the text of a new track.
Ignoring zero alpha channels avoids this.

Reproduced on Ubuntu 24.04. Arch Linux requires "noto-fonts-emoji".

[radioactiveman]

@jlindgren90: Do you think this is a valid fix? I'm still not sure how and why it works. My first guess was alpha channels should never be negative, but clamping the value to 0..1 does not help.

The other commit only optimizes the font handling code. It's not required to fix #1491.

[jlindgren90]

I'd like to understand why draw_text is called with a < 0 in the first place. That shouldn't happen.

[radioactiveman]

It's because of using floating point math. I think comparing against 0 in ui_infoarea_do_fade() is not correct. Using an epsilon avoids -0.1 values.

The early return in draw_text() is still needed though to fix the emoji issue. But we can use an epsilon here as well.

diff --git a/src/gtkui/ui_infoarea.cc b/src/gtkui/ui_infoarea.cc
index c59f35a33..31a090031 100644
--- a/src/gtkui/ui_infoarea.cc
+++ b/src/gtkui/ui_infoarea.cc
@@ -17,6 +17,7 @@
  * the use of this software.
  */
 
+#include <float.h>
 #include <math.h>
 #include <string.h>
 
@@ -140,7 +141,7 @@ G_GNUC_END_IGNORE_DEPRECATIONS
 static void draw_text (GtkWidget * widget, cairo_t * cr, int x, int y, int
  width, float r, float g, float b, float a, int font_size, const char * text)
 {
-    if (a < 0)
+    if (a <= FLT_EPSILON)
         return;
 
     cairo_move_to (cr, x, y);
@@ -285,7 +286,7 @@ static void ui_infoarea_do_fade (void *)
         done = false;
     }
 
-    if (area->last_alpha > 0)
+    if (area->last_alpha > FLT_EPSILON)
     {
         area->last_alpha -= 0.1;
         done = false;

[jlindgren90]

How about this? jlindgren90@f754d97

[radioactiveman]

LGTM and it's also more like the code for qtui. Minor suggestion: Use ALPHA_STEPS also in TO_ALPHA().

However It does not fix the issue. Can you reproduce it?
Such special characters can be found for example here: https://emojipedia.org
The issue is that the alpha channel has no effect on them. Even with a zero value they are still visible.

Edit: Screenshot and sample code:

#include <gtk/gtk.h>

static void draw_text (GtkWidget *widget, cairo_t *cr, int x, int y,
                       float r, float g, float b, float a, const char *text)
{
    //if (a <= 0)
    //    return;

    cairo_move_to (cr, x, y);
    cairo_set_source_rgba (cr, r, g, b, a);

    PangoLayout * layout = gtk_widget_create_pango_layout (widget, text);
    pango_cairo_show_layout (cr, layout);
    g_object_unref (layout);
}

static gboolean draw_cb (GtkWidget *widget, cairo_t *cr)
{
    draw_text (widget, cr, 10, 10, 0, 0, 0, 1.0, "Alpha 1.0: 😄");
    draw_text (widget, cr, 10, 30, 0, 0, 0, 0.8, "Alpha 0.8: 😄");
    draw_text (widget, cr, 10, 50, 0, 0, 0, 0.6, "Alpha 0.6: 😄");
    draw_text (widget, cr, 10, 70, 0, 0, 0, 0.4, "Alpha 0.4: 😄");
    draw_text (widget, cr, 10, 90, 0, 0, 0, 0.2, "Alpha 0.2: 😄");
    draw_text (widget, cr, 10, 110, 0, 0, 0, 0.0, "Alpha 0.0: 😄");

    return TRUE;
}

int main (int argc, char *argv[])
{
    GtkWidget *window, *drawing_area;

    gtk_init (&argc, &argv);

    window = gtk_window_new (GTK_WINDOW_TOPLEVEL);
    gtk_widget_set_size_request (window, 240, 140);

    drawing_area = gtk_drawing_area_new ();
    gtk_container_add (GTK_CONTAINER (window), drawing_area);

    g_signal_connect (drawing_area, "draw", G_CALLBACK (draw_cb), NULL);
    g_signal_connect (window, "destroy", G_CALLBACK (gtk_main_quit), NULL);

    gtk_widget_show_all (window);

    gtk_main ();

    return 0;
}

[jlindgren90]

Interesting, let's add a zero check as a workaround like you suggested then.

[radioactiveman]

Updated accordingly and added a comment. I included also your patch.

[jlindgren90]

LGTM, thanks