allow setting prerender state with a function too

bin/style.js

@@ -1820,11 +1820,12 @@ module.exports = {
             {"z": 16, "val": 10},
             {"z": 17, "val": 11}
         ],
-        "hillshade_prerender_size": [
+        "hillshade_prerender": [
             "stops",
-            {"z": 13, "val": 1024 },
-            {"z": 14, "val": 512 }
-        ]
+            {"z": 13, "val": 0},
+            {"z": 14, "val": 1}
+        ],
+        "hillshade_prerender_size": 1024
     },
     "classes": [
         {
@@ -1977,7 +1978,7 @@ module.exports = {
                 "hillshade_full_shadow": {
                     "color": "#103",
                     "antialias": false,
-                    "prerender": true,
+                    "prerender": "hillshade_prerender",
                     "prerender-size": "hillshade_prerender_size",
                     "prerender-blur": 1,
                     "opacity": [
@@ -1992,7 +1993,7 @@ module.exports = {
                 "hillshade_medium_shadow": {
                     "color": "#206",
                     "antialias": false,
-                    "prerender": true,
+                    "prerender": "hillshade_prerender",
                     "prerender-size": "hillshade_prerender_size",
                     "prerender-blur": 1,
                     "opacity": [
@@ -2007,7 +2008,7 @@ module.exports = {
                 "hillshade_full_highlight": {
                     "color": "#fffff3",
                     "antialias": false,
-                    "prerender": true,
+                    "prerender": "hillshade_prerender",
                     "prerender-size": "hillshade_prerender_size",
                     "prerender-blur": 1,
                     "opacity": [
@@ -2022,7 +2023,7 @@ module.exports = {
                 "hillshade_medium_highlight": {
                     "color": "#ffd",
                     "antialias": false,
-                    "prerender": true,
+                    "prerender": "hillshade_prerender",
                     "prerender-size": "hillshade_prerender_size",
                     "prerender-blur": 1,
                     "opacity": [
@@ -2789,7 +2790,7 @@ module.exports = {
                 "hillshade_full_shadow": {
                     "color": "#103",
                     "antialias": false,
-                    "prerender": true,
+                    "prerender": "hillshade_prerender",
                     "prerender-size": "hillshade_prerender_size",
                     "prerender-blur": 1,
                     "opacity": [
@@ -2803,7 +2804,7 @@ module.exports = {
                 "hillshade_medium_shadow": {
                     "color": "#206",
                     "antialias": false,
-                    "prerender": true,
+                    "prerender": "hillshade_prerender",
                     "prerender-size": "hillshade_prerender_size",
                     "prerender-blur": 1,
                     "opacity": [
@@ -2817,7 +2818,7 @@ module.exports = {
                 "hillshade_full_highlight": {
                     "color": "#fdfdad",
                     "antialias": false,
-                    "prerender": true,
+                    "prerender": "hillshade_prerender",
                     "prerender-size": "hillshade_prerender_size",
                     "prerender-blur": 1,
                     "opacity": [
@@ -2832,7 +2833,7 @@ module.exports = {
                 "hillshade_medium_highlight": {
                     "color": "#ffe1b7",
                     "antialias": false,
-                    "prerender": true,
+                    "prerender": "hillshade_prerender",
                     "prerender-size": "hillshade_prerender_size",
                     "prerender-blur": 1,
                     "opacity": [

include/llmr/style/properties.hpp

@@ -93,7 +93,7 @@ struct GenericClass {
     boost::optional<TranslateAnchor> translateAnchor;
     boost::optional<FunctionProperty> opacity;
     boost::optional<PropertyTransition> opacity_transition;
-    float prerender = false;
+    boost::optional<FunctionProperty> prerender;
     boost::optional<FunctionProperty> prerenderBuffer;
     boost::optional<FunctionProperty> prerenderSize;
     boost::optional<FunctionProperty> prerenderBlur;
@@ -110,13 +110,17 @@ struct GenericProperties {
     std::array<float, 2> translate = {{ 0, 0 }};
     TranslateAnchor translateAnchor = TranslateAnchor::Map;
     float opacity = 1.0;
-    bool prerender;
 
     // These are unresolved properties because the value here is per tile, so it might differ.
+    boost::optional<FunctionProperty> prerender;
     boost::optional<FunctionProperty> prerenderBuffer;
     boost::optional<FunctionProperty> prerenderSize;
     boost::optional<FunctionProperty> prerenderBlur;
 
+    inline bool getPrerender(int8_t z) const {
+        return prerender && prerender.get().evaluate<bool>(z);
+    }
+
     // Obtains prerender properties by integer zoom level.
     inline PrerenderProperties getPrerenderProperties(int8_t z) const {
         PrerenderProperties props;

src/renderer/painter_fill.cpp

@@ -152,10 +152,8 @@ void Painter::renderFill(FillBucket& bucket, const std::string& layer_name, cons
                                            : defaultFillProperties;
     if (!properties.enabled) return;
 
-    if (properties.prerender) {
+    if (properties.prerender && properties.getPrerender(id.z)) {
         if (pass == Translucent) {
-
-
             // Buffer value around the 0..4096 extent that will be drawn into the 256x256 pixel
             // texture. We later scale the texture so that the actual bounds will align with this
             // tile's bounds. The reason we do this is so that the

src/style/style_parser.cpp

@@ -557,7 +557,7 @@ void StyleParser::parseGenericClass(GenericClass &klass, JSVal value) {
     }
 
     if (value.HasMember("prerender")) {
-        klass.prerender = parseBoolean(value["prerender"]);
+        klass.prerender = parseFunction(value["prerender"]);
     }
 
     if (value.HasMember("prerender-buffer")) {