Show user-visible error when no camera is available.

data/camera.css

@@ -1,8 +1,3 @@
-.errorbox {
-    background: #dd0000;
-    color: #ffffff;
-}
-
 .controlbox {
     background: rgba(0, 0, 0, 0.2);
 }
@@ -12,6 +7,11 @@
     background-color: rgba(0, 0, 0, 0.2);
 }
 
+.error-overlay {
+    opacity: 0.9;
+    background-color: rgba(255, 0, 0, 0.2);
+}
+
 .flash {
     background-color: #ffffff;
 }

data/camera.ui

@@ -110,6 +110,61 @@
                     </style>
                   </object>
                 </child>
+                <child type="overlay">
+                  <object class="GtkBox" id="message-box">
+                    <property name="orientation">vertical</property>
+                    <property name="halign">fill</property>
+                    <property name="valign">center</property>
+                    <property name="spacing">5</property>
+                    <property name="can-focus">0</property>
+                    <property name="visible">0</property>
+                    <child>
+                      <object class="GtkLabel" id="message-label">
+                        <property name="label">Error happened</property>
+                        <property name="vexpand">1</property>
+                        <property name="hexpand">1</property>
+                        <property name="valign">start</property>
+                        <property name="margin-start">5</property>
+                        <property name="margin-end">5</property>
+                        <property name="margin-top">5</property>
+                        <property name="margin-bottom">5</property>
+                        <property name="can-focus">0</property>
+                      </object>
+                    </child>
+                    <child>
+                      <object class="GtkButton">
+                        <property name="visible">0</property>
+                        <property name="halign">start</property>
+                        <property name="margin-start">5</property>
+                        <property name="margin-end">5</property>
+                        <property name="margin-top">5</property>
+                        <property name="margin-bottom">5</property>
+                        <child>
+                          <object class="GtkBox">
+                            <property name="orientation">horizontal</property>
+                            <property name="spacing">10</property>
+                            <child>
+                              <object class="GtkLabel">
+                                <property name="label">Error</property>
+                              </object>
+                            </child>
+                            <child>
+                              <object class="GtkImage">
+                                <property name="icon-name">dialog-warning-symbolic</property>
+                              </object>
+                            </child>
+                          </object>
+                        </child>
+                        <style>
+                          <class name="destructive-action"/>
+                        </style>
+                      </object>
+                    </child>
+                    <style>
+                      <class name="error-overlay"/>
+                    </style>
+                  </object>
+                </child>
                 <child type="overlay">
                   <object class="GtkBox" id="bottom-box">
                     <property name="orientation">horizontal</property>

src/main.c

@@ -63,6 +63,9 @@ GtkWidget *scanned_codes;
 GtkWidget *preview_top_box;
 GtkWidget *preview_bottom_box;
 
+GtkWidget *message_box;
+GtkWidget *message_label;
+
 GtkWidget *flash_button;
 GtkWidget *iso_button;
 GtkWidget *shutter_button;
@@ -89,6 +92,13 @@ remap(int value, int input_min, int input_max, int output_min, int output_max)
         return (int)result;
 }
 
+static void
+display_error(const char *message)
+{
+        gtk_label_set_label(GTK_LABEL(message_label), message);
+        gtk_widget_set_visible(message_box, true);
+}
+
 bool
 check_window_active()
 {
@@ -162,8 +172,7 @@ update_state(const mp_state_main *new_state)
         state.focus.max = new_state->focus.max;
         state.focus.manual = new_state->focus.manual;
 
-        state.has_auto_focus_continuous =
-                new_state->has_auto_focus_continuous;
+        state.has_auto_focus_continuous = new_state->has_auto_focus_continuous;
         state.has_auto_focus_start = new_state->has_auto_focus_start;
 
         state.preview_buffer_width = new_state->preview_buffer_width;
@@ -357,10 +366,8 @@ position_preview(float *offset_x, float *offset_y, float *size_x, float *size_y)
         }
 
         int scale_factor = gtk_widget_get_scale_factor(preview);
-        int top_height =
-                gtk_widget_get_height(preview_top_box) * scale_factor;
-        int bottom_height =
-                gtk_widget_get_height(preview_bottom_box) * scale_factor;
+        int top_height = gtk_widget_get_height(preview_top_box) * scale_factor;
+        int bottom_height = gtk_widget_get_height(preview_bottom_box) * scale_factor;
         int inner_height = state.preview_height - top_height - bottom_height;
 
         float scale = (float)MIN(state.preview_width / (float)buffer_width,
@@ -519,6 +526,8 @@ preview_resize(GtkWidget *widget, int width, int height, gpointer data)
         if (state.preview_width != width || state.preview_height != height) {
                 state.preview_width = width;
                 state.preview_height = height;
+                if (state.configuration->count == 0)
+                        return TRUE;
                 update_io_pipeline();
         }
 
@@ -898,9 +907,11 @@ flash_button_clicked(GtkWidget *button, gpointer user_data)
 static void
 on_realize(GtkWidget *window, gpointer *data)
 {
+        if (state.configuration->count == 0) {
+                return;
+        }
         GtkNative *native = gtk_widget_get_native(window);
         mp_process_pipeline_init_gl(gtk_native_get_surface(native));
-
         state.camera = state.configuration->cameras[0];
         update_io_pipeline();
 }
@@ -988,14 +999,14 @@ static gboolean
 fb_profile_to_state(GValue *value, GVariant *variant, gpointer user_data)
 {
         const gchar *name;
-        gboolean state = FALSE;
+        gboolean fb_state = FALSE;
 
         name = g_variant_get_string(variant, NULL);
 
         if (g_strcmp0(name, "full") == 0)
-                state = TRUE;
+                fb_state = TRUE;
 
-        g_value_set_boolean(value, state);
+        g_value_set_boolean(value, fb_state);
 
         return TRUE;
 }
@@ -1005,9 +1016,9 @@ state_to_fb_profile(const GValue *value,
                     const GVariantType *expected_type,
                     gpointer user_data)
 {
-        gboolean state = g_value_get_boolean(value);
+        gboolean fb_state = g_value_get_boolean(value);
 
-        return g_variant_new_string(state ? "full" : "silent");
+        return g_variant_new_string(fb_state ? "full" : "silent");
 }
 
 static void
@@ -1194,6 +1205,9 @@ activate(GtkApplication *app, gpointer data)
         preview_bottom_box =
                 GTK_WIDGET(gtk_builder_get_object(builder, "bottom-box"));
 
+        message_box = GTK_WIDGET(gtk_builder_get_object(builder, "message-box"));
+        message_label = GTK_WIDGET(gtk_builder_get_object(builder, "message-label"));
+
         g_signal_connect(window, "realize", G_CALLBACK(on_realize), NULL);
 
         g_signal_connect(preview, "realize", G_CALLBACK(preview_realize), NULL);
@@ -1317,7 +1331,11 @@ activate(GtkApplication *app, gpointer data)
                 g_application_get_dbus_connection(G_APPLICATION(app));
         mp_flash_gtk_init(conn);
 
-        mp_io_pipeline_start();
+        if (state.configuration->count > 0) {
+                mp_io_pipeline_start();
+        } else {
+                display_error("No camera found");
+        }
 
         gtk_application_add_window(app, GTK_WINDOW(window));
         gtk_widget_set_visible(window, true);