Add meter/level display

INSTALL.md

@@ -8,6 +8,12 @@ Linux Kernel with the ALSA Scarlett2 Protocol Driver.
   for the Gen 2 support.
 - For Clarett+ 8Pre support, you need 6.1.
 - For the other Clarett USB and Clarett+ models, you need 6.7.
+- For the level meters to work, you need 6.7.
+
+If you don't have 6.7, you can get the driver from here and build it
+for your current kernel:
+
+https://github.com/geoffreybennett/scarlett-gen2/releases/tag/v6.5.11c1
 
 ## Enabling the Driver
 

USAGE.md

@@ -354,8 +354,8 @@ menu option File → Interface Simulation to load.
 - Can’t select (focus) the gain/volume controls or use a keyboard to
   adjust them.
 
-- Level (monitoring) doesn’t work yet and is disabled (needs kernel
-  driver update).
+- Level meters don’t work if you're not running the driver from Linux
+  6.7.
 
 - Load/Save uses `alsactl` which will be confused if the ALSA
   interface name (e.g. `USB`) changes.

src/menu.c

@@ -125,7 +125,7 @@ GMenu *create_app_menu(GtkApplication *app) {
   g_menu_append_submenu(menu, "_View", G_MENU_MODEL(view_menu));
   g_menu_append(view_menu, "_Routing", "win.routing");
   g_menu_append(view_menu, "_Mixer",   "win.mixer");
-//g_menu_append(view_menu, "_Levels",  "win.levels");
+  g_menu_append(view_menu, "_Levels",  "win.levels");
   g_menu_append(view_menu, "_Startup", "win.startup");
 
   GMenu *help_menu = g_menu_new();

src/window-levels.c

@@ -24,7 +24,17 @@ static int update_levels_controls(void *user_data) {
     // go through the ports in that category
     for (int j = 0; j < card->routing_out_count[i]; j++) {
       GtkWidget *meter = card->meters[meter_num];
-      gtk_dial_set_value(GTK_DIAL(meter), values[meter_num]);
+      double value = 20 * log10(values[meter_num] / 4095.0);
+
+      int int_value;
+      if (value < -80)
+        int_value = -80;
+      else if (value > 0)
+        int_value = 0;
+      else
+        int_value = round(value);
+
+      gtk_dial_set_value(GTK_DIAL(meter), int_value);
       meter_num++;
     }
   }
@@ -93,7 +103,7 @@ GtkWidget *create_levels_controls(struct alsa_card *card) {
         count_labels[j] = add_count_label(grid, j);
 
       // create the meter widget and attach to the grid
-      GtkWidget *meter = gtk_dial_new_with_range(0, 4096, 1);
+      GtkWidget *meter = gtk_dial_new_with_range(-80, 0, 1);
       card->meters[meter_num++] = meter;
       gtk_grid_attach(GTK_GRID(grid), meter, j + 1, i + 1, 1, 1);
     }