png2sprites: allow user to change transparent colour

2 files changed, 24 insertions, 4 deletions

diff --git a/docs/tools.md b/docs/tools.md
index acc5e60..0899411 100644
--- a/docs/tools.md
+++ b/docs/tools.md
@@ -65,9 +65,11 @@ The result is 1 bit per pixel data without colour information. The colour will
 be provided as part of the `attr` field in the `sprite_attr` struct when
 calling [ubox_set_sprite_attr](ubox-lib-ref.html#ubox_set_sprite_attr).
 
-The tool interprets dark grey (RGB: 28, 28, 28) as transparent in the MSX
-palette, and any other colour will be used as visible monochrome data. If the
-image has more than one colour, it will be used to identify different sprites.
+The tool interprets dark grey (RGB: 28, 28, 28) as transparent in the MSX palette
+by default, but that can be changed with the `-t` or `--transparent` flag and a 6
+digit hexadecimal value as parameter. Any other colour will be used as visible
+monochrome data. If the image has more than one colour, it will be used to identify
+different sprites.
 
 For example:
 
diff --git a/tools/png2sprites.py b/tools/png2sprites.py
index 95e6492..d51251f 100755
--- a/tools/png2sprites.py
+++ b/tools/png2sprites.py
@@ -21,6 +21,7 @@
 # THE SOFTWARE.
 #
 
+import re
 from argparse import ArgumentParser
 from PIL import Image
 
@@ -29,9 +30,18 @@ __version__ = "1.0"
 DEF_W = 16
 DEF_H = 16
 
+RE_COL = re.compile("^#?([0-9A-Fa-f]{2})([0-9A-Fa-f]{2})([0-9A-Fa-f]{2})$")
 TRANS = (28, 28, 28)
 
 
+def to_color_tuple(src):
+    g = RE_COL.search(src)
+    if g:
+        return int(g.group(1), 16), int(g.group(2), 16), int(g.group(3), 16)
+    else:
+        raise Exception("hexadecimal RRGGBB color expected")
+
+
 def to_hex_list_str(src):
     out = ""
     for i in range(0, len(src), 8):
@@ -79,6 +89,14 @@ def main():
         action="store_true",
         help="include frame color as a comment",
     )
+    parser.add_argument(
+        "-t",
+        "--transparent",
+        dest="trans_color",
+        type=to_color_tuple,
+        default="1c1c1c",
+        help="redefine transparent color in 6-digit hexadecimal notation (default: 1c1c1c)",
+    )
 
     parser.add_argument("image", help="image to convert")
 
@@ -109,7 +127,7 @@ def main():
             tile = [
                 data[x + i + ((y + j) * w)] for j in range(DEF_H) for i in range(DEF_W)
             ]
-            cols = sorted(set([c for c in tile if c != TRANS]))
+            cols = sorted(set([c for c in tile if c != args.trans_color]))
 
             if not cols:
                 continue