Find nearest approximation for 24-bit colors in 256-color AttrSpecs

Palette entries can only distinguish between "low" and "high" colors, so
there's no way for a user to specify different colors for 88, 256, and
24-bit color screens.  Prior to this change, someone wanting to specify
a 24-bit color but have their applicaiton also work when running in
256-color mode would have to maintain two different palette entries, or
do a color conversion themselves to avoid an AttrSpec error.

With this change, an AttrSpec with colors=256 will instead convert
24-bit foreground and/or background colors to the nearest color from the
256-color palette.  In most cases this is what the user will want, and
if they want to handle 256-color mode separately, they can still do so.
This just makes it easier to support both 24-bit and 8-bit color modes.

1 files changed, 16 insertions, 2 deletions

diff --git a/urwid/display_common.py b/urwid/display_common.py
index 878bbc9..8361b45 100755
--- a/urwid/display_common.py
+++ b/urwid/display_common.py
@@ -386,6 +386,20 @@ def _parse_color_256(desc):
     except ValueError:
         return None
 
+
+def _true_to_256(desc):
+
+    if  not (desc.startswith('#') and len(desc) == 7):
+        return None
+
+    c256 = _parse_color_256("#" + "".join([
+        format(int(x, 16)//16, "x")
+        for x in [desc[1:3], desc[3:5], desc[5:7] ]
+    ]
+    ))
+    return _color_desc_256(c256)
+
+
 def _parse_color_88(desc):
     """
     Return a color number for the description desc.
@@ -616,7 +630,7 @@ class AttrSpec(object):
                 scolor = _parse_color_true(part)
                 flags |= _FG_TRUE_COLOR
             else:
-                scolor = _parse_color_256(part)
+                scolor = _parse_color_256(_true_to_256(part) or part)
                 flags |= _FG_HIGH_COLOR
             # _parse_color_*() return None for unrecognised colors
             if scolor is None:
@@ -658,7 +672,7 @@ class AttrSpec(object):
             color = _parse_color_true(background)
             flags |= _BG_TRUE_COLOR
         else:
-            color = _parse_color_256(background)
+            color = _parse_color_256(_true_to_256(background) or background)
             flags |= _BG_HIGH_COLOR
         if color is None:
             raise AttrSpecError(("Unrecognised color specification " +