Use contrast color for tag text

It's hard to read tags with light background colors and white text.
This patch uses YIQ method to set text color to black or white,
depending on which is the more contrasting to the background color.

app/helpers/tags_helper.rb

@@ -12,20 +12,29 @@ module TagsHelper
   #   * open_only   - Boolean. Whenever link to the filter with "open" issues
   #                   only limit.
   def render_tag_link(tag, options = {})
+    use_colors = RedmineTags.settings[:issues_use_colors].to_i > 0
+    if use_colors
+      tag_bg_color = tag_color(tag)
+      tag_fg_color = tag_fg_color(tag_bg_color)
+      tag_style = "background-color: #{tag_bg_color}; color: #{tag_fg_color}"
+    end
+
     filters = [[:tags, '=', tag.name]]
     filters << [:status_id, 'o'] if options[:open_only]
     if options[:use_search]
-      content = link_to tag, { controller: 'search', action: 'index',
-        id: @project, q: tag.name, wiki_pages: true, issues: true }
+      content =  link_to tag, { controller: 'search', action: 'index',
+        id: @project, q: tag.name, wiki_pages: true, issues: true,
+        style: tag_style }
     else
       content = link_to_filter tag.name, filters, project_id: @project
     end
     if options[:show_count]
       content << content_tag('span', "(#{ tag.count })", class: 'tag-count')
     end
-    style = if RedmineTags.settings[:issues_use_colors].to_i > 0
+
+    style = if use_colors 
         { class: 'tag-label-color',
-          style: "background-color: #{ tag_color tag }" }
+          style: tag_style }
       else
         { class: 'tag-label' }
       end
@@ -37,6 +46,15 @@ def tag_color(tag)
     "##{ Digest::MD5.hexdigest(tag_name)[0..5] }"
   end
 
+  def tag_fg_color(bg_color)
+    # calculate contrast text color according to YIQ method
+    # http://24ways.org/2010/calculating-color-contrast/
+    r = bg_color[1..2].hex
+    g = bg_color[3..4].hex
+    b = bg_color[5..6].hex
+    (r * 299 + g * 587 + b * 114) >= 128000 ? "black" : "white"
+  end
+
   # Renders list of tags
   # Clouds are rendered as block <tt>div</tt> with internal <tt>span</t> per tag.
   # Lists are rendered as unordered lists <tt>ul</tt>. Lists are ordered by

assets/stylesheets/redmine_tags.css

@@ -12,7 +12,7 @@ ul.tags li { margin: .25em 0px; }
 
 table.list tr.issue .tag-label-color a,
 .tags .tag-label-color a,
-.issue .tag-label-color a { color: white; }
+.issue .tag-label-color a { color: inherit; }
 
 tr.issue td.tags {
   text-align: left;

config/locales/sk.yml

@@ -0,0 +1,23 @@
+# Preložil samo.forus@microstep-mis.com
+sk:
+  tags: Tagy
+  field_tags: Tagy
+  field_tag_list: Tagy
+  setting_issue_tags: Tagy úlohy
+  issues_sidebar: Zobraziť tagy v bočnom paneli ako
+  issues_show_count: Počet zobrazených úloh
+  issues_open_only: Zobraziť len otvorené úlohy
+  issues_sort_by: Zoradiť tagy podľa
+  issues_use_colors: Použiť farby
+
+  issue_tags_sidebar_none: Nezobrazovať
+  issue_tags_sidebar_list: Zoznam
+  issue_tags_sidebar_cloud: Cloud
+  issue_tags_sidebar_simple_cloud: Jednoduchý cloud
+
+  issues_sort_by_name: Názov
+  issues_sort_by_count: Počet úloh
+  issues_sort_order_asc: Vzostupne
+  issues_sort_order_desc: Zostupne
+
+  auto_complete_new_tag: Pridať...