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sbapp/kivymd/theming_dynamic_text.py

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+"""
+Theming Dynamic Text
+====================
+
+Two implementations. The first is based on color brightness obtained from-
+https://www.w3.org/TR/AERT#color-contrast
+The second is based on relative luminance calculation for sRGB obtained from-
+https://www.w3.org/TR/2008/REC-WCAG20-20081211/#relativeluminancedef
+and contrast ratio calculation obtained from-
+https://www.w3.org/TR/2008/REC-WCAG20-20081211/#contrast-ratiodef
+
+Preliminary testing suggests color brightness more closely matches the
+`Material Design spec` suggested text colors, but the alternative implementation
+is both newer and the current 'correct' recommendation, so is included here
+as an option.
+"""
+
+
+def _color_brightness(color):
+    # Implementation of color brightness method
+    brightness = color[0] * 299 + color[1] * 587 + color[2] * 114
+    brightness = brightness
+    return brightness
+
+
+def _black_or_white_by_color_brightness(color):
+    if _color_brightness(color) >= 500:
+        return "black"
+    else:
+        return "white"
+
+
+def _normalized_channel(color):
+    # Implementation of contrast ratio and relative luminance method
+    if color <= 0.03928:
+        return color / 12.92
+    else:
+        return ((color + 0.055) / 1.055) ** 2.4
+
+
+def _luminance(color):
+    rg = _normalized_channel(color[0])
+    gg = _normalized_channel(color[1])
+    bg = _normalized_channel(color[2])
+    return 0.2126 * rg + 0.7152 * gg + 0.0722 * bg
+
+
+def _black_or_white_by_contrast_ratio(color):
+    l_color = _luminance(color)
+    l_black = 0.0
+    l_white = 1.0
+    b_contrast = (l_color + 0.05) / (l_black + 0.05)
+    w_contrast = (l_white + 0.05) / (l_color + 0.05)
+    return "white" if w_contrast >= b_contrast else "black"
+
+
+def get_contrast_text_color(color, use_color_brightness=True):
+    if use_color_brightness:
+        contrast_color = _black_or_white_by_color_brightness(color)
+    else:
+        contrast_color = _black_or_white_by_contrast_ratio(color)
+    if contrast_color == "white":
+        return 1, 1, 1, 1
+    else:
+        return 0, 0, 0, 1
+
+
+if __name__ == "__main__":
+    from kivy.utils import get_color_from_hex
+
+    from kivymd.color_definitions import colors, text_colors
+
+    for c in colors.items():
+        if c[0] in ["Light", "Dark"]:
+            continue
+        color = c[0]
+        print(f"For the {color} color palette:")
+        for name, hex_color in c[1].items():
+            if hex_color:
+                col = get_color_from_hex(hex_color)
+                col_bri = get_contrast_text_color(col)
+                con_rat = get_contrast_text_color(
+                    col, use_color_brightness=False
+                )
+                text_color = text_colors[c[0]][name]
+                print(
+                    f"   The {name} hue gives {col_bri} using color "
+                    f"brightness, {con_rat} using contrast ratio, and "
+                    f"{text_color} from the MD spec"
+                )