Render entrances.

New layer "entrances", with entrance and access tags.

Render entrances starting at z=17. Most entrances are rendered with a
hollow square marker. Entrances marked as "main" are rendered with a
solid square, "service" entrances with corners of a hollow square and
entrances with access="no" with a hollow square with a line along a
diagonal.

The marker brightness reflects the access permissions of the entrance.
Entrances with access="yes" and "permissive" have a darker color.
Markers with other access tag values have the same color as the building
perimeter line.

Exits, such as entrance=exit and entrance=emergency are not rendered.

Address label text-halo-radius is increased at z>=18 to improve
readability of labels on top of entrance markers.

addressing.mss

@@ -34,8 +34,11 @@
     text-wrap-width: 30; // 3.0 em
     text-line-spacing: -1.5; // -0.15 em
     text-margin: 3; // 0.3 em
-    [zoom >= 18]["addr_unit" != null]["addr_housenumber" = null] {
-      text-name: [addr_unit];
+    [zoom >= 18] {
+      text-halo-radius: @standard-halo-radius * 1.25;
+      ["addr_unit" != null]["addr_housenumber" = null] {
+        text-name: [addr_unit];
+      }
     }
     [zoom >= 20] {
         text-size: 11;

buildings.mss

@@ -5,6 +5,8 @@
 @building-major-fill: darken(@building-fill, 20%);
 @building-major-line: darken(@building-major-fill, 25%);
 
+@entrance-permissive: darken(@building-line, 15%);
+@entrance-normal: @building-line;
 
 #buildings {
   [zoom >= 13] {
@@ -42,3 +44,44 @@
     polygon-fill: #B8B8B8;
   }
 }
+
+#entrances {
+  ["entrance" != null] {
+    marker-fill: @entrance-normal;
+    marker-allow-overlap: true;
+    marker-ignore-placement: true;
+    marker-file: url('symbols/rect.svg');
+    ["entrance" = "main"] {
+      marker-file: url('symbols/square.svg');
+    }
+    ["entrance" = "service"] {
+      marker-file: url('symbols/corners.svg');
+    }
+    ["access" = "yes"],["access" = "permissive"] {
+      marker-fill: @entrance-permissive;
+    }
+    ["access" = "no"] {
+      marker-fill: @entrance-normal;
+      marker-file: url('symbols/rectdiag.svg');
+    }
+    ["entrance" = "exit"],["entrance" = "emergency"] {
+      marker-opacity: 0.0;
+    }
+    [zoom >= 17] {
+      marker-width: 4.0;
+      marker-height: 4.0;
+    }
+    [zoom >= 18] {
+      marker-width: 6;
+      marker-height: 6;
+    }
+    [zoom >= 19] {
+      marker-width: 8.0;
+      marker-height: 8.0;
+    }
+    [zoom >= 20] {
+      marker-width: 10;
+      marker-height: 10;
+    }
+  }
+}

project.mml

@@ -1068,6 +1068,22 @@ Layer:
         ) AS guideways
     properties:
       minzoom: 13
+  - id: entrances
+    geometry: point
+    <<: *extents
+    Datasource:
+      <<: *osm2pgsql
+      table: |-
+        (SELECT
+            way,
+            tags->'entrance' AS entrance,
+            access
+          FROM planet_osm_point
+          WHERE tags->'indoor' = 'no'
+            OR tags->'indoor' IS NULL)
+        AS entrances
+    properties:
+      minzoom: 17
   - id: aeroways
     geometry: linestring
     <<: *extents