Add support for darker prints

This adds the -e/--energy switch, which lets us specify the thermal
energy to the printer. It's a value between 0x0000 (light) and 0xffff
(darker).

catprinter/cmds.py

@@ -94,7 +94,25 @@ def cmd_set_energy(val):
         0,
         0xff,
     ])
-    b_arr[7] = chk_sum(b_arr, 6, 2)
+    b_arr[8] = chk_sum(b_arr, 6, 2)
+    return bs(b_arr)
+
+
+def cmd_apply_energy():
+    b_arr = bs(
+        [
+            81,
+            120,
+            -66,
+            0,
+            1,
+            0,
+            1,
+            0,
+            0xff,
+        ]
+    )
+    b_arr[7] = chk_sum(b_arr, 6, 1)
     return bs(b_arr)
 
 
@@ -167,13 +185,12 @@ def cmd_print_row(img_row):
     return b_arr
 
 
-def cmds_print_img(img, dark_mode=False):
-
-    PRINTER_MODE = CMD_PRINT_TEXT if dark_mode else CMD_PRINT_IMG
-
+def cmds_print_img(img, energy: int = 0xffff):
     data = \
         CMD_GET_DEV_STATE + \
         CMD_SET_QUALITY_200_DPI + \
+        cmd_set_energy(energy) + \
+        cmd_apply_energy() + \
         CMD_LATTICE_START
     for row in img:
         data += cmd_print_row(row)

print.py

@@ -35,9 +35,9 @@ def parse_args():
                           'If omitted, the the script will try to auto discover '
                           'the printer based on its advertised BLE services.'
                       ))
-    args.add_argument('-t', '--darker', action='store_true',
-                      help="Print the image in text mode. This leads to more contrast, \
-                          but slower speed.")
+    args.add_argument('-e', '--energy', type=lambda h: int(h.removeprefix("0x"), 16),
+                      help="Thermal energy. Between 0x0000 (light) and 0xffff (darker)",
+                      default="0xffff")
     return args.parse_args()
 
 
@@ -72,7 +72,7 @@ def main():
         return
 
     logger.info(f'✅ Read image: {bin_img.shape} (h, w) pixels')
-    data = cmds_print_img(bin_img, dark_mode=args.darker)
+    data = cmds_print_img(bin_img, energy=args.energy)
     logger.info(f'✅ Generated BLE commands: {len(data)} bytes')
 
     # Try to autodiscover a printer if --device is not specified.