move clip_altitudes() to base RenderEngine

src/c3nav/mapdata/render/engines/base.py

@@ -2,6 +2,8 @@ import math
 from abc import ABC, abstractmethod
 from typing import Optional
 
+from shapely.ops import unary_union
+
 
 class FillAttribs:
     __slots__ = ('color', 'opacity')
@@ -42,11 +44,26 @@ class RenderEngine(ABC):
 
         self.background_rgb = tuple(int(background[i:i + 2], 16) for i in range(1, 6, 2))
 
+        # keep track which area of the image has which altitude currently
+        self.altitudes = {}
+        self.last_altitude = None
+
     @abstractmethod
     def get_png(self) -> bytes:
         # render the image to png.
         pass
 
+    def clip_altitudes(self, new_geometry, new_altitude=None):
+        # register new geometry with an altitude
+        # a geometry with no altitude will reset the altitude information of its area as if nothing was ever there
+        if self.last_altitude is not None and self.last_altitude > new_altitude:
+            raise ValueError('Altitudes have to be ascending.')
+
+        if new_altitude in self.altitudes:
+            self.altitudes[new_altitude] = unary_union([self.altitudes[new_altitude], new_geometry])
+        else:
+            self.altitudes[new_altitude] = new_geometry
+
     def add_geometry(self, geometry, fill: Optional[FillAttribs] = None, stroke: Optional[StrokeAttribs] = None,
                      altitude=None, height=None, shape_cache_key=None):
         # draw a shapely geometry with a given style

src/c3nav/mapdata/render/engines/svg.py

@@ -6,12 +6,11 @@ from itertools import chain
 from typing import Optional
 
 import numpy as np
+from PIL import Image
 from django.conf import settings
 from django.core import checks
-from PIL import Image
 from shapely.affinity import translate
 from shapely.geometry import LineString, Polygon
-from shapely.ops import unary_union
 
 # import gobject-inspect, cairo and rsvg if the native rsvg SVG_RENDERER should be used
 from c3nav.mapdata.render.engines.base import FillAttribs, RenderEngine, StrokeAttribs
@@ -47,10 +46,6 @@ class SVGEngine(RenderEngine):
         self.defs = ''
         self.clip_path_i = 0
 
-        # keep track which area of the image has which altitude currently
-        self.altitudes = {}
-        self.last_altitude = None
-
         # for fast numpy operations
         self.np_scale = np.array((self.scale, -self.scale))
         self.np_offset = np.array((-self.minx * self.scale, self.maxy * self.scale))
@@ -201,23 +196,6 @@ class SVGEngine(RenderEngine):
         shadow = self._create_geometry(shadow_geom, attribs)
         self.g += shadow
 
-    def clip_altitudes(self, new_geometry, new_altitude=None):
-        # register new geometry with specific (or no) altitude
-        # a geometry with no altitude will reset the altitude information of its area as if nothing was ever there
-        for altitude, geometry in tuple(self.altitudes.items()):
-            if altitude != new_altitude:
-                self.altitudes[altitude] = geometry.difference(new_geometry)
-                if self.altitudes[altitude].is_empty:
-                    self.altitudes.pop(altitude)
-        if new_altitude is not None:
-            if self.last_altitude is not None and self.last_altitude > new_altitude:
-                raise ValueError('Altitudes have to be ascending.')
-            self.last_altitude = new_altitude
-            if new_altitude in self.altitudes:
-                self.altitudes[new_altitude] = unary_union([self.altitudes[new_altitude], new_geometry])
-            else:
-                self.altitudes[new_altitude] = new_geometry
-
     def _add_geometry(self, geometry, fill: Optional[FillAttribs] = None, stroke: Optional[StrokeAttribs] = None,
                       altitude=None, height=None, shape_cache_key=None):