Use black fonts to improve text readability

4 files changed, 45 insertions, 9 deletions

diff --git a/budgetscreen.py b/budgetscreen.py
index 48e952b..432a237 100644
--- a/budgetscreen.py
+++ b/budgetscreen.py
@@ -125,10 +125,18 @@ class BudgetScreen(Gtk.VBox):
             # If there is no category, display as Unknown
             if c is '':
                 description = _('Unknown')
-            catbox = Gtk.Label(label=description)
-            catbox.set_padding(10, 0)
 
             color = colors.get_category_color_str(c)
+            if colors.is_too_light(color):
+                font_color = '#000000'
+            else:
+                font_color = '#FFFFFF'
+
+            catbox = Gtk.Label()
+            catbox.set_markup(
+                '<span color="%s">%s</span>' % (font_color, description))
+
+            catbox.set_padding(10, 0)
 
             ebox = Gtk.EventBox()
             parse, color = Gdk.Color.parse(color)
diff --git a/chartscreen.py b/chartscreen.py
index 94f765d..139a48c 100644
--- a/chartscreen.py
+++ b/chartscreen.py
@@ -130,18 +130,24 @@ class ChartScreen(Gtk.VBox):
             # If there is no category, display as Unknown
             if c is '':
                 description = _('Unknown')
+
+            color = colors.get_category_color_str(c)
+            if colors.is_too_light(color):
+                font_color = '#000000'
+            else:
+                font_color = '#FFFFFF'
+
             catlabel = Gtk.Label()
             catlabel.set_markup(
-                '<span size="x-large" color="white">%s</span>' % description)
+                '<span size="x-large" color="%s">%s</span>' % (font_color,
+                                                               description))
             catlabel.props.margin = 10
             catgroup.add_widget(catlabel)
 
-            color = colors.get_category_color_str(c)
-
             amountlabel = Gtk.Label()
             amountlabel.set_markup(
-                '<span size="x-large" color="white">%s</span>' %
-                locale.currency(self.category_total[c]))
+                '<span size="x-large" color="%s">%s</span>' %
+                (font_color, locale.currency(self.category_total[c])))
             amountgroup.add_widget(amountlabel)
 
             hbox.pack_start(catlabel, True, True, 20)
diff --git a/colors.py b/colors.py
index af75e1a..161c0e6 100644
--- a/colors.py
+++ b/colors.py
@@ -1,3 +1,5 @@
+import logging
+
 CREDIT_COLOR = '#009900'
 
 DEBIT_COLOR = '#ff4040'
@@ -41,3 +43,21 @@ def get_category_color_str(catname):
     color = get_category_color(catname)
     return "#%02x%02x%02x" % \
         (int(color[0] * 255), int(color[1] * 255), int(color[2] * 255))
+
+
+def is_too_light(color):
+    return _luminance(color) > 96
+
+
+def _luminance(color):
+    ''' Calculate luminance value '''
+    return int(color[1:3], 16) * 0.3 + int(color[3:5], 16) * 0.6 + \
+        int(color[5:7], 16) * 0.1
+
+
+def test_luminances():
+    for cat_color in CATEGORY_COLORS:
+        color = "#%02x%02x%02x" % \
+            (int(cat_color[0] * 255), int(cat_color[1] * 255),
+             int(cat_color[2] * 255))
+        logging.error('color %s luminance %s', color, _luminance(color))
diff --git a/registerscreen.py b/registerscreen.py
index e5d9d46..0797e67 100644
--- a/registerscreen.py
+++ b/registerscreen.py
@@ -200,8 +200,10 @@ class RegisterScreen(Gtk.VBox):
         category = t['category']
         cell_renderer.set_property('text', category)
         if category:
-            cell_renderer.set_property(
-                'background', colors.get_category_color_str(category))
+            category_color = colors.get_category_color_str(category)
+            cell_renderer.set_property('background', category_color)
+            if not colors.is_too_light(category_color):
+                cell_renderer.set_property('foreground', '#FFFFFF')
         else:
             cell_renderer.set_property('background', None)