Refactor building into table function

data.yml

@@ -104,7 +104,7 @@ Layer:
     Datasource: 
       dbname: osm
       extent: -20037508.34,-20037508.34,20037508.34,20037508.34
-      geometry_field: way
+      geometry_field: geom
       geometry_table: ''
       host: db
       key_field: ''
@@ -112,22 +112,8 @@ Layer:
       max_size: 512
       password: osm
       port: 5432
-      srid: ''
-      table: |-
-        ( SELECT
-            osm_id,
-            way,
-            least(greatest(3, COALESCE(height, levels*3.66,5)),400)^.7 AS render_height
-          FROM (
-              SELECT osm_id, ST_Simplify(way, 10) AS way, height, levels FROM building_z13
-              WHERE z(!scale_denominator!) = 13
-              UNION ALL
-              SELECT * FROM building_z14
-              WHERE z(!scale_denominator!) >= 14
-          ) AS water
-          WHERE way && !bbox!
-          ORDER BY render_height, ST_YMin(way) DESC
-        ) AS data
+      srid: 900913
+      table: (SELECT * FROM layer_building(!bbox!, z(!scale_denominator!))) AS t
       type: postgis
       user: osm
     description: Buildings

schema/layers/building.sql

@@ -5,3 +5,20 @@ CREATE OR REPLACE VIEW building_z13 AS (
 CREATE OR REPLACE VIEW building_z14 AS (
     SELECT osm_id, way, height, levels FROM buildings
 );
+
+CREATE OR REPLACE FUNCTION layer_building(bbox geometry, zoom_level int)
+RETURNS TABLE(geom geometry, osm_id bigint, render_height float) AS $$
+    WITH zoom_levels AS (
+        SELECT osm_id, ST_Simplify(way, 10) AS way, height, levels FROM building_z13
+        WHERE zoom_level = 13
+        UNION ALL
+        SELECT * FROM building_z14
+        WHERE zoom_level >= 14
+    )
+    SELECT way, osm_id,
+    least(greatest(3, COALESCE(height, levels*3.66,5)),400)^.7 AS render_height
+    FROM zoom_levels
+    WHERE way && bbox
+    ORDER BY render_height, ST_YMin(way) DESC;
+$$ LANGUAGE SQL IMMUTABLE;
+