Update colour.py

website/utils/colour.py

@@ -1,4 +1,5 @@
 import hashlib
+from website.constants import BACKGROUND_COLOUR
 
 def _contrast(c1, c2):
     # https://www2.cs.sfu.ca/CourseCentral/820/li/material/RGB-YUV.pdf
@@ -10,9 +11,28 @@ def _contrast(c1, c2):
 def _distance_sq(c1, c2):
     return sum((i / 256 - j / 256) ** 2 for i, j in zip(c1, c2))
 
-def gen_colour(seed, background):
+def _gen_colour(seed, background=BACKGROUND_COLOUR):
+    '''
+    Returns a colour that with sufficient contrast to the background colour
+    '''
     while True:
         seed = hashlib.sha256(seed).digest()
-        colour = seed[:3]
-        if 1.5 < _contrast(colour, background):
+        for i in range(0, len(seed) - len(seed) % 3, 3):
+            colour = seed[i:i+3]
+            if 1.5 < _contrast(colour, background):
+                return colour
+
+def gen_colour(seed, background=BACKGROUND_COLOUR, *avoid):
+    '''
+    Returns a colour that with sufficient contrast to the background colour
+    Tries to make the colour contrast with all the colours in `avoid`
+    '''
+    best_colour, best_score = None, None
+    for _ in range(16384):
+        colour = _gen_colour(seed, background)
+        score = float('inf') if len(avoid) == 0 else sum(_contrast(colour, c) for c in avoid) / len(avoid)
+        if 1.25 < score:
             return colour
+        if best_score == None or score > best_score:
+            best_colour = colour
+    return best_colour