Only write XML rules that apply to minzoom/maxzoom of the containing layer

[nimix]

If a layer is restricted to certain zoom levels by minzoom/maxzoom properties it can get rule that can never apply for this layer because they only apply for scales outside minzoom/maxzoom. The following example output shows a case were only one of the rules is needed:

<Style name="place1" filter-mode="first">
  <Rule>
    <MaxScaleDenominator>50000</MaxScaleDenominator>
    <MinScaleDenominator>5000</MinScaleDenominator>
    <Filter>([type] = 'hamlet')</Filter>
    <TextSymbolizer fontset-name="fontset-1" fill="#000000" placement="point" wrap-width="65" minimum-distance="10" halo-radius="2" halo-fill="#ffffff" size="10"><![CDATA[[name]]]></TextSymbolizer>
  </Rule>
  <Rule>
    <MaxScaleDenominator>200000</MaxScaleDenominator>
    <MinScaleDenominator>50000</MinScaleDenominator>
    <Filter>([type] = 'suburb')</Filter>
    <TextSymbolizer fontset-name="fontset-1" fill="#000000" placement="point" wrap-width="65" minimum-distance="10" halo-radius="2" halo-fill="#ffffff" size="10"><![CDATA[[name]]]></TextSymbolizer>
  </Rule>
  <Rule>
    <MaxScaleDenominator>50000</MaxScaleDenominator>
    <MinScaleDenominator>5000</MinScaleDenominator>
    <Filter>([type] = 'village')</Filter>
    <TextSymbolizer size="12" fontset-name="fontset-1" fill="#000000" placement="point" wrap-width="65" minimum-distance="10" halo-radius="2" halo-fill="#ffffff"><![CDATA[[name]]]></TextSymbolizer>
  </Rule>
  <Rule>
    <MaxScaleDenominator>200000</MaxScaleDenominator>
    <MinScaleDenominator>50000</MinScaleDenominator>
    <Filter>([type] = 'village')</Filter>
    <TextSymbolizer fontset-name="fontset-1" fill="#000000" placement="point" wrap-width="65" minimum-distance="10" halo-radius="2" halo-fill="#ffffff" size="10"><![CDATA[[name]]]></TextSymbolizer>
  </Rule>
  <Rule>
    <MaxScaleDenominator>100000</MaxScaleDenominator>
    <MinScaleDenominator>12500</MinScaleDenominator>
    <Filter>([type] = 'town')</Filter>
    <TextSymbolizer size="12" halo-fill="#ffffff" placement="point" wrap-width="65" minimum-distance="10" fontset-name="fontset-0" halo-radius="2" fill="#222222"><![CDATA[[name]]]></TextSymbolizer>
  </Rule>
  <Rule>
    <MaxScaleDenominator>400000</MaxScaleDenominator>
    <MinScaleDenominator>100000</MinScaleDenominator>
    <Filter>([type] = 'town')</Filter>
    <TextSymbolizer halo-fill="#ffffff" placement="point" wrap-width="65" minimum-distance="10" size="10" fontset-name="fontset-0" halo-radius="2" fill="#222222"><![CDATA[[name]]]></TextSymbolizer>
  </Rule>
  <Rule>
    <MaxScaleDenominator>1500000</MaxScaleDenominator>
    <MinScaleDenominator>400000</MinScaleDenominator>
    <Filter>([type] = 'town')</Filter>
    <TextSymbolizer placement="point" wrap-width="65" minimum-distance="10" size="10" fontset-name="fontset-0" halo-radius="2" fill="#222222" halo-fill="#eeeeee"><![CDATA[[name]]]></TextSymbolizer>
  </Rule>
  <Rule>
    <MaxScaleDenominator>50000</MaxScaleDenominator>
    <MinScaleDenominator>25000</MinScaleDenominator>
    <Filter>([type] = 'city')</Filter>
    <TextSymbolizer size="14" placement="point" wrap-width="65" minimum-distance="10" fontset-name="fontset-0" halo-radius="2" fill="#222222" halo-fill="#eeeeee"><![CDATA[[name]]]></TextSymbolizer>
  </Rule>
  <Rule>
    <MaxScaleDenominator>1500000</MaxScaleDenominator>
    <MinScaleDenominator>50000</MinScaleDenominator>
    <Filter>([type] = 'city')</Filter>
    <TextSymbolizer size="12" placement="point" wrap-width="65" minimum-distance="10" fontset-name="fontset-0" halo-radius="2" fill="#222222" halo-fill="#eeeeee"><![CDATA[[name]]]></TextSymbolizer>
  </Rule>
  <Rule>
    <MaxScaleDenominator>50000000</MaxScaleDenominator>
    <MinScaleDenominator>1500000</MinScaleDenominator>
    <Filter>([type] = 'city')</Filter>
    <TextSymbolizer placement="point" wrap-width="65" minimum-distance="10" fontset-name="fontset-0" halo-radius="2" fill="#222222" size="10" halo-fill="#eeeeee"><![CDATA[[name]]]></TextSymbolizer>
  </Rule>
  <Rule>
    <MaxScaleDenominator>200000000</MaxScaleDenominator>
    <MinScaleDenominator>50000000</MinScaleDenominator>
    <Filter>([type] = 'country')</Filter>
    <TextSymbolizer size="10" fontset-name="fontset-1" halo-radius="2" fill="#222222" halo-fill="#eeeeee" placement="point" wrap-width="65" minimum-distance="10"><![CDATA[[name]]]></TextSymbolizer>
  </Rule>
  <Rule>
    <MaxScaleDenominator>200000000</MaxScaleDenominator>
    <MinScaleDenominator>100000000</MinScaleDenominator>
    <Filter>([type] = 'continent')</Filter>
    <TextSymbolizer size="14" fontset-name="fontset-0" halo-radius="2" fill="#222222" halo-fill="#eeeeee" placement="point" wrap-width="65" minimum-distance="10"><![CDATA[[name]]]></TextSymbolizer>
  </Rule>
  <Rule>
    <MaxScaleDenominator>500000000</MaxScaleDenominator>
    <MinScaleDenominator>200000000</MinScaleDenominator>
    <Filter>([type] = 'continent')</Filter>
    <TextSymbolizer size="12" fontset-name="fontset-0" halo-radius="2" fill="#222222" halo-fill="#eeeeee" placement="point" wrap-width="65" minimum-distance="10"><![CDATA[[name]]]></TextSymbolizer>
  </Rule>
</Style>
<Layer name="place1"
  maximum-scale-denominator="50000000"
  minimum-scale-denominator="1500000"
  srs="+proj=merc +a=6378137 +b=6378137 +lat_ts=0.0 +lon_0=0.0 +x_0=0.0 +y_0=0 +k=1.0 +units=m +nadgrids=@null +no_defs +over">
    <StyleName>place1</StyleName>
  </Layer>

[nebulon42]

Interesting observation, thanks. For building a test case could you please add the relevant portions of the MML and MSS files?

[nimix]

Here you go:
MML

{
  "bounds": [
    -180,
    -85.05112877980659,
    180,
    85.05112877980659
  ],
  "center": [
    0,
    0,
    2
  ],
  "format": "png",
  "interactivity": false,
  "minzoom": 0,
  "maxzoom": 22,
  "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",
  "Stylesheet": [
    "places.mms"
  ],
  "Layer": [
    {
      "geometry": "point",
      "extent": [
        -179.99999692067183,
        -84.96651228427098,
        179.99999692067183,
        84.96651228427099
      ],
      "Datasource": {
        "type": "postgis",
        "table": "(SELECT name, geom, type::text,\"type\" as \"order\" FROM oepnv_places WHERE type IN ('continent','country') ORDER BY \"order\" ASC, population DESC) AS places",
        "key_field": "",
        "geometry_field": "geom",
        "srid": "900913",
        "extent_cache": "custom",
        "extent": "-20037508,-19929239,20037508,19929239",
        "host": "localhost",
        "dbname": "gis",
        "user": "render",
        "port": "5432"
      },
      "properties": {
        "minzoom": 0,
        "maxzoom": 3
      },
      "id": "place0",
      "class": "place",
      "srs-name": "custom",
      "srs": "+proj=merc +a=6378137 +b=6378137 +lat_ts=0.0 +lon_0=0.0 +x_0=0.0 +y_0=0 +k=1.0 +units=m +nadgrids=@null +no_defs +over",
      "advanced": {
        "srid": "900913"
      },
      "name": "place0"
    },
    {
      "geometry": "point",
      "extent": [
        -179.99999692067183,
        -84.96651228427098,
        179.99999692067183,
        84.96651228427099
      ],
      "Datasource": {
        "type": "postgis",
        "table": "(SELECT name, geom, type::text,\"type\" as \"order\" FROM oepnv_places WHERE type IN ('continent','country','city') ORDER BY \"order\" ASC, population DESC) AS places",
        "key_field": "",
        "geometry_field": "geom",
        "srid": "900913",
        "extent_cache": "custom",
        "extent": "-20037508,-19929239,20037508,19929239",
        "host": "localhost",
        "dbname": "gis",
        "user": "render",
        "port": "5432"
      },
      "properties": {
        "minzoom": 4,
        "maxzoom": 8
      },
      "id": "place1",
      "class": "place",
      "srs-name": "custom",
      "srs": "+proj=merc +a=6378137 +b=6378137 +lat_ts=0.0 +lon_0=0.0 +x_0=0.0 +y_0=0 +k=1.0 +units=m +nadgrids=@null +no_defs +over",
      "advanced": {
        "srid": "900913"
      },
      "name": "place1"
    },
    {
      "geometry": "point",
      "extent": [
        -179.99999692067183,
        -84.96651228427098,
        179.99999692067183,
        84.96651228427099
      ],
      "Datasource": {
        "type": "postgis",
        "table": "(SELECT name, geom, type::text,\"type\" as \"order\" FROM oepnv_places ORDER BY \"order\" ASC, population DESC) AS places",
        "key_field": "",
        "geometry_field": "geom",
        "srid": "900913",
        "extent_cache": "custom",
        "extent": "-20037508,-19929239,20037508,19929239",
        "host": "localhost",
        "dbname": "gis",
        "user": "render",
        "port": "5432"
      },
      "properties": {
        "minzoom": 9,
        "maxzoom": 22
      },
      "id": "place2",
      "class": "place",
      "srs-name": "custom",
      "srs": "+proj=merc +a=6378137 +b=6378137 +lat_ts=0.0 +lon_0=0.0 +x_0=0.0 +y_0=0 +k=1.0 +units=m +nadgrids=@null +no_defs +over",
      "advanced": {
        "srid": "900913"
      },
      "name": "place2"
    }
  ],
  "scale": 1,
  "metatile": 2,
  "name": "oepnvkarte",
  "description": ""
}

MSS

@ozean: #a1cbea;
@land: #f1eee8;

@book-fonts: "DejaVu Sans Book","Unifont Medium";
@bold-fonts: "DejaVu Sans Bold","Unifont Medium";
@oblique-fonts: "DejaVu Sans Oblique","Unifont Medium";

Map {
  background-color: @ozean;
}

.place
{
    [type="continent"][zoom<=2]{
      [zoom>=1]{
        text-name: "[name]";
        text-size: 12;
        text-face-name: @bold-fonts;
        text-halo-radius: 2;
        text-fill: #222;
        text-halo-fill: #eee;
        text-placement: point;
        text-wrap-width: 65;    
        text-min-distance: 10;
      }
      [zoom>=2]{text-size: 14;}
    }
    [type="country"][zoom<=3]{
      [zoom>=2]{
        text-name: "[name]";
        text-size: 10;
        text-face-name: @book-fonts;
        text-halo-radius: 2;
        text-fill: #222;
        text-halo-fill: #eee;
        text-placement: point;
        text-wrap-width: 65;    
        text-min-distance: 10;
      }
      [zoom>=4]{
        text-face-name: @bold-fonts;
        text-size: 12;
      }
    }
    [type="city"][zoom<=14]{
      [zoom>=4]{
        text-placement: point;
        text-wrap-width: 65;    
        text-min-distance: 10;
        text-name: "[name]";
        text-face-name: @bold-fonts;
        text-halo-radius: 2;
        text-fill: #222;
        text-size: 10;
        text-halo-fill: #eee;
      }
      [zoom>=9]{text-size: 12;}
      [zoom>=14]{text-size: 14;}
    }
    [type="town"][zoom<=15]
    {
      [zoom>=9]{
        text-placement: point;
        text-wrap-width: 65;    
        text-min-distance: 10;
        text-size: 10;
        text-name: "[name]";
        text-face-name: @bold-fonts;
        text-halo-radius: 2;
        text-fill: #222;
        text-size: 10;
        text-halo-fill: #eee;
      }
      [zoom>=11] { text-halo-fill: #fff; }
      [zoom>=13]{
        text-size: 12;
      }
    }
    [type="village"][zoom<=16]{
      [zoom>=12]{
        text-face-name: @book-fonts;
        text-fill: #000;
        text-placement: point;
        text-wrap-width: 65;    
        text-min-distance: 10;
        text-halo-radius: 2;
        text-halo-fill: #fff;
        text-name: "[name]";
        text-size: 10;
      }
      [zoom>=14]{text-size: 12;}
    }
    [type="suburb"][zoom<=13]{
      [zoom>=12]{
        text-face-name: @book-fonts;
        text-fill: #000;
        text-placement: point;
        text-wrap-width: 65;    
        text-min-distance: 10;
        text-halo-radius: 2;
        text-halo-fill: #fff;
        text-name: "[name]";
        text-size: 10;
      }
    }
    [type="hamlet"][zoom<=16]{
      [zoom>=14]{
        text-face-name: @book-fonts;
        text-fill: #000;
        text-placement: point;
        text-wrap-width: 65;    
        text-min-distance: 10;
        text-halo-radius: 2;
        text-halo-fill: #fff;
        text-name: "[name]";
        text-size: 10;
      }
    }
}

[nebulon42]

Was not that difficult to fix. What's great is that I noticed a nearly 3s shorter compile time for openstreetmap-carto on my machine, which is a speed increase of 20%.

But it is important to test that there are no rendering problems. A quick test with osm-carto revealed no problems so far.
@nimix Could you please test your style if it still looks as expected?

cc @pnorman @rory

[nebulon42]

Performance is a tricky topic for me. I did some benchmarking because I wanted to release 0.18 and while I got 14% improvement in processing time for osm-carto I got 97% degradation for OSM Bright. The lines decreased slightly by 100 or so for osm-carto but doubled for OSM Bright.

This is unacceptable for release. I have to investigate what causes this. Maybe I will have to revert the change.

[nebulon42]

The problem described above was none. It was caused by the fact that a regression for OSM Bright reduced the parsing time by half.