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colour.py

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+import hashlib
+
+def _contrast(c1, c2):
+    # https://www2.cs.sfu.ca/CourseCentral/820/li/material/RGB-YUV.pdf
+    l1 = (0.299 * c1[0] + 0.587 * c1[1] + 0.114 * c1[2]) / 256
+    l2 = (0.299 * c2[0] + 0.587 * c2[1] + 0.114 * c2[2]) / 256
+    # https://www.accessibility-developer-guide.com/knowledge/colours-and-contrast/how-to-calculate/
+    return (l1 + 0.05) / (l2 + 0.05)
+
+def _distance_sq(c1, c2):
+    return sum((i / 256 - j / 256) ** 2 for i, j in zip(c1, c2))
+
+def gen_colour(seed, background):
+    while True:
+        seed = hashlib.sha256(seed).digest()
+        colour = seed[:3]
+        if 1.5 < _contrast(colour, background):
+            return colour