Use a random symbology for forests

This adds a random symbology for forests, lightens forests, and
unifies natural=wood and landuse=forest rendering.

Using http://www.imagico.de/map/jsdotpattern.php a random pattern
was generated from the SVG

    <path d="m 3.5,0 -3.5,3.5 0,0.5 0.5,0 2.5,-2.5 0,2
    -3,3 0,0.5 0.5,0 2.5,-2.5 0,5.5
    1,0 0,-5.5 2.5,2.5 0.5,0 0,-0.5 -3,-3 0,-2
    2.5,2.5 0.5,0 0,-0.5 z" fill="rgb(58,135,39)"/>

    <path d="m 10.5,0 a 2.5,3 0 0,1 0,6 l 0,-1
    a 1.5,2 0 0,0 0,-4
    a 1.5,2 0 0,0 0,4 l 0,1
    a 2.5,3 0 0,1 0,-6
    z" fill="rgb(58,135,39)"/>

This was then converted with GIMP into a PNG which Mapnik can use.

The forest fill was lightened, but there are now darker symbols on.

This necessitated adjusting the text colour for forests, which was
done in Lch colour space. The frequent symbols also required some
halo adjustments.

There are multiple interpretations in use of landuse=forest vs.
natural=wood. Rather than attempt to sort this out when the tagging
has not settled, the same appearance is used for both.

This commit doesn't use different symbologies for different types
of forests (mixed/coniferous/broad_leaved/palm) (gravitystorm#822), but that
can be considered later.

Fixes gravitystorm#938
Fixes forest part of gravitystorm#937

amenity-points.mss

@@ -700,24 +700,6 @@
     text-placement: interior;
   }
 
-  [feature = 'natural_wood'][is_building = 'no'] {
-    [zoom >= 8][way_pixels > 3000],
-    [zoom >= 17] {
-      text-name: "[name]";
-      text-size: @landcover-font-size;
-      [way_pixels > 12000] { text-size: @landcover-font-size-big; }
-      [way_pixels > 48000] { text-size: @landcover-font-size-bigger; }
-      text-fill: darken(@wood, 40%);
-      text-face-name: @landcover-face-name;
-      text-halo-radius: 1;
-      text-halo-fill: rgba(255,255,255,0.6);
-      text-wrap-width: @landcover-wrap-width-size;
-      [way_pixels > 12000] {text-wrap-width: @landcover-wrap-width-size-big; }
-      [way_pixels > 48000] {text-wrap-width: @landcover-wrap-width-size-bigger; }
-      text-placement: interior;
-    }
-  }
-
   [feature = 'natural_peak'],
   [feature = 'natural_volcano'] {
     [zoom >= 13] {
@@ -1129,17 +1111,18 @@
     }
   }
 
+  [feature = 'natural_wood'][is_building = 'no'],
   [feature = 'landuse_forest'][is_building = 'no'] {
     [zoom >= 8][way_pixels > 3000],
     [zoom >= 17] {
       text-name: "[name]";
       text-size: @landcover-font-size;
       [way_pixels > 12000] { text-size: @landcover-font-size-big; }
       [way_pixels > 48000] { text-size: @landcover-font-size-bigger; }
-      text-fill: darken(@forest, 30%);
+      text-fill: @forest-text;
       text-face-name: @landcover-face-name;
       text-halo-radius: 1;
-      text-halo-fill: rgba(255,255,255,0.6);
+      text-halo-fill: @forest-text-halo;
       text-wrap-width: @landcover-wrap-width-size;
       [way_pixels > 12000] {text-wrap-width: @landcover-wrap-width-size-big; }
       [way_pixels > 48000] {text-wrap-width: @landcover-wrap-width-size-bigger; }

landcover.mss

@@ -1,10 +1,11 @@
 // --- Parks, woods, other green things ---
 
-@forest: #a0cf85;
+@forest: #b2d6a3;            // Lch(82,30,135)
+@forest-text: #4e843e;       // Lch(50,45,135) (mix of @forest and polygon-pattern)
+@forest-text-halo: #d0f5c1;  // Lch(92.8, 30, 135)
 @grass: #cfeca8; // also meadow, common, garden, village_green, conservation
 @golf_course: #b5e3b5;
 @park: #cdf7c9; // also recreation_ground
-@wood: #aed1a0;
 @vineyard: #b3e2a8;
 @grassland: #c6e4b4;
 
@@ -250,18 +251,13 @@
     }
   }
 
-  [feature = 'landuse_forest'] {
+  [feature = 'landuse_forest'],
+  [feature = 'natural_wood'] {
     [zoom >= 8] {
       polygon-fill: @forest;
       [way_pixels >= 4]  { polygon-gamma: 0.75; }
       [way_pixels >= 64] { polygon-gamma: 0.3;  }
     }
-    [zoom >= 14] {
-      polygon-pattern-file: url('symbols/forest.png');
-      [way_pixels >= 4]  { polygon-pattern-gamma: 0.75; }
-      [way_pixels >= 64] { polygon-pattern-gamma: 0.3;  }
-    }
-
   }
 
   [feature = 'landuse_farmyard'][zoom >= 10] {
@@ -377,14 +373,6 @@
     }
   }
 
-  [feature = 'natural_wood'] {
-    [zoom >= 8] {
-      polygon-fill: @wood;
-      [way_pixels >= 4]  { polygon-gamma: 0.75; }
-      [way_pixels >= 64] { polygon-gamma: 0.3;  }
-    }
-  }
-
   [feature = 'natural_bare_rock'][zoom >= 9] {
     polygon-fill: @bare_ground;
     [way_pixels >= 4]  { polygon-gamma: 0.75; }
@@ -546,13 +534,18 @@
 }
 
 #landuse-overlay {
-  [landuse = 'military'][zoom >= 10]::landuse {
+  [feature = 'military'][zoom >= 10] {
     polygon-pattern-file: url('symbols/military_red_hatch.png');
     polygon-pattern-alignment: global;
     line-color: @military;
     line-width: 3;
     line-opacity: 0.329;
   }
+  [feature = 'forest'][zoom >= 12]  {
+    polygon-pattern-file: url('symbols/forest.png'); // Lch(50,60,135)
+    polygon-pattern-alignment: global;
+    opacity: 0.6; // The entire layer has opacity in case of overlapping forests
+  }
 }
 
 #cliffs {

project.mml

@@ -525,7 +525,7 @@
       "srs": "+proj=merc +a=6378137 +b=6378137 +lat_ts=0.0 +lon_0=0.0 +x_0=0.0 +y_0=0.0 +k=1.0 +units=m +nadgrids=@null +wktext +no_defs +over", 
       "Datasource": {
         "extent": "-20037508,-20037508,20037508,20037508", 
-        "table": "(SELECT\n    way, landuse, leisure\n  FROM planet_osm_polygon\n  WHERE (landuse = 'military') AND building IS NULL\n) AS landuse_overlay", 
+        "table": "(SELECT\n    way, COALESCE(landuse, CASE WHEN \"natural\" = 'wood' THEN 'forest' END) AS feature\n  FROM planet_osm_polygon\n  WHERE (landuse IN ('military', 'forest') OR \"natural\" = 'wood')\n    AND building IS NULL\n) AS landuse_overlay", 
         "geometry_field": "way", 
         "type": "postgis", 
         "key_field": "", 

project.yaml

@@ -503,9 +503,10 @@ Layer:
       <<: *osm2pgsql
       table: |-
         (SELECT
-            way, landuse, leisure
+            way, COALESCE(landuse, CASE WHEN "natural" = 'wood' THEN 'forest' END) AS feature
           FROM planet_osm_polygon
-          WHERE (landuse = 'military') AND building IS NULL
+          WHERE (landuse IN ('military', 'forest') OR "natural" = 'wood')
+            AND building IS NULL
         ) AS landuse_overlay
     advanced: {}
   - id: "line-barriers"