event-widget: make more CSS compliant

There are some other changes:
1. Renamed widget class to "event-widget" to avoid collisions
2. Added contrasting event title coloring
3. Use gtk_render functions

data/theme/gtk-styles.css

@@ -36,15 +36,32 @@
     font: bold;
 }
 
-.event {
+.event-widget {
-    border: darker(@borders) 1px solid;
     border-radius: 2px;
     margin-top: 3px;
     margin-left: 6px;
     margin-bottom: 3px;
     margin-right: 6px;
     padding: 4px;
-    font: 9;
+    font: 10;
+}
+
+GcalEventWidget.color-dark {
+    color: white;
+    outline-color: rgba(0, 0, 0, 0.3);
+}
+
+GcalEventWidget.color-dark:backdrop {
+    color: rgba(255, 255, 255, 0.3);
+}
+
+GcalEventWidget.color-light {
+    color: black;
+    outline-color: rgba(255, 255, 255, 0.5);
+}
+
+GcalEventWidget.color-light:backdrop {
+    color: rgba(0, 0, 0, 0.3);
 }
 
 .event-details .frame {

src/gcal-event-widget.c

@@ -20,6 +20,8 @@
 #include "gcal-event-widget.h"
 #include "gcal-utils.h"
 
+#define INTENSITY(r, g, b) ((r) * 0.30 + (g) * 0.59 + (b) * 0.11)
+
 typedef struct
 {
   /* properties */
@@ -216,7 +218,7 @@ gcal_event_widget_init(GcalEventWidget *self)
 
   gtk_style_context_add_class (
       gtk_widget_get_style_context (GTK_WIDGET (self)),
-      "event");
+      "event-widget");
 }
 
 static void
@@ -257,15 +259,39 @@ gcal_event_widget_set_property (GObject      *object,
       priv->summary = g_value_dup_string (value);
       return;
     case PROP_COLOR:
-      if (priv->color != NULL)
+      {
-        gdk_rgba_free (priv->color);
+        GtkStyleContext *context;
 
-      priv->color = g_value_dup_boxed (value);
+        context = gtk_widget_get_style_context (GTK_WIDGET (object));
-      gtk_widget_override_background_color (
+
-          GTK_WIDGET (object),
+        if (priv->color != NULL)
-          gtk_widget_get_state_flags (GTK_WIDGET (object)),
+          gdk_rgba_free (priv->color);
-          priv->color);
+
-      return;
+        priv->color = g_value_dup_boxed (value);
+
+        if (priv->color == NULL)
+          return;
+
+        gtk_widget_override_background_color (
+            GTK_WIDGET (object),
+            gtk_widget_get_state_flags (GTK_WIDGET (object)),
+            priv->color);
+
+        if (INTENSITY (priv->color->red,
+                       priv->color->green,
+                       priv->color->blue) > 0.5)
+          {
+            gtk_style_context_remove_class (context, "color-dark");
+            gtk_style_context_add_class (context, "color-light");
+          }
+        else
+          {
+            gtk_style_context_remove_class (context, "color-light");
+            gtk_style_context_add_class (context, "color-dark");
+          }
+
+        return;
+      }
     case PROP_DTSTART:
       if (priv->dt_start != NULL)
         g_free (priv->dt_start);
@@ -538,7 +564,6 @@ gcal_event_widget_draw (GtkWidget *widget,
   PangoLayout *layout;
   PangoRectangle logical_rect;
   PangoFontDescription *font_desc;
-  GdkRGBA fg_color;
 
   priv = gcal_event_widget_get_instance_private (GCAL_EVENT_WIDGET (widget));
   context = gtk_widget_get_style_context (widget);
@@ -546,7 +571,6 @@ gcal_event_widget_draw (GtkWidget *widget,
 
   gtk_style_context_get_padding (context, state, &padding);
   gtk_style_context_get_margin (context, state, &margin);
-  gtk_style_context_get_color (context, state, &fg_color);
 
   x = margin.left;
   y = margin.top;
@@ -577,14 +601,10 @@ gcal_event_widget_draw (GtkWidget *widget,
       pango_layout_set_width (layout, (width - (padding.left + padding.right + left_gap) ) * PANGO_SCALE);
     }
 
-  cairo_set_source_rgba (cr,
+  gtk_render_layout (context, cr,
-                         fg_color.red,
+                     x + padding.left + left_gap,
-                         fg_color.green,
+                     y + padding.top,
-                         fg_color.blue,
+                     layout);
-                         fg_color.alpha);
-  cairo_move_to (cr, x + padding.left + left_gap, y + padding.top);
-  pango_cairo_show_layout (cr, layout);
-
 
   /* render icon */
   if (priv->has_reminders)