feat: add kernel ACPI support for querying battery percentage, add battery indicator to desktop, move log state to 0:/state directory

programs/src/desktop/panel.cpp

@@ -210,6 +210,33 @@ void gui::desktop_draw_panel(DesktopState* ds) {
     } else {
         ds->wifi_icon_rect = {0, 0, 0, 0};
     }
+
+    // Battery, leftmost of the status icons.  Only a machine that reported a
+    // battery device at startup gets one; a desktop shows nothing here.
+    if (ds->battery_present && ds->icon_battery.pixels) {
+        ds->battery_icon_rect = {next_icon_x, icon_y, 16, 16};
+        next_icon_x -= 16 + 10;
+
+        // The glyph already encodes level and charging state, and the charging
+        // variants carry their own green, so it is blitted as loaded.  A
+        // critical battery is the one case worth shouting about.
+        if (ds->battery_info.present && ds->battery_info.critical
+            && !ds->battery_info.charging) {
+            uint32_t* src = ds->icon_battery.pixels;
+            uint32_t tinted[256];
+            for (int p = 0; p < 16 * 16; p++) {
+                uint8_t a = (src[p] >> 24) & 0xFF;
+                tinted[p] = ((uint32_t)a << 24) | 0x00CC3333;
+            }
+            fb.blit_alpha(ds->battery_icon_rect.x, icon_y, 16, 16, tinted);
+        } else {
+            fb.blit_alpha(ds->battery_icon_rect.x, icon_y,
+                          ds->icon_battery.width, ds->icon_battery.height,
+                          ds->icon_battery.pixels);
+        }
+    } else {
+        ds->battery_icon_rect = {0, 0, 0, 0};
+    }
 }
 
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