charger: Draw battery percentage over charger screen

Let user know the exact battery capacity.

Change-Id: Ie2abaeee0e443cd2a730780488287ad4d9ea1e9a

charger/charger.c

@@ -658,6 +658,20 @@ static void android_green(void)
     gr_color(0xa4, 0xc6, 0x39, 255);
 }
 
+static void draw_capacity(struct charger *charger)
+{
+    char cap_str[64];
+    int x, y;
+    int str_len_px;
+
+    snprintf(cap_str, sizeof(cap_str), "%d%%", charger->batt_anim->capacity);
+    str_len_px = gr_measure(cap_str);
+    x = (gr_fb_width() - str_len_px) / 2;
+    y = (gr_fb_height() + char_height) / 2;
+    android_green();
+    gr_text(x, y, cap_str, 0);
+}
+
 /* returns the last y-offset of where the surface ends */
 static int draw_surface_centered(struct charger *charger, gr_surface surface)
 {
@@ -710,8 +724,10 @@ static void redraw_screen(struct charger *charger)
     /* try to display *something* */
     if (batt_anim->capacity < 0 || batt_anim->num_frames == 0)
         draw_unknown(charger);
-    else
+    else {
         draw_battery(charger);
+        draw_capacity(charger);
+    }
     gr_flip();
 }