Allow property functions for prerender properties, but tie them to the tile's zoom level instead of the map zoom level

fixes #253

include/llmr/renderer/painter.hpp

@@ -85,9 +85,9 @@ public:
     void renderText(TextBucket& bucket, const std::string& layer_name, const Tile::ID& id);
     void renderRaster(RasterBucket& bucket, const std::string& layer_name, const Tile::ID& id);
 
-    void preparePrerender(const GenericProperties &properties);
-    void finishPrerender(const GenericProperties &properties);
-    void renderPrerenderedTexture(Bucket &bucket, const GenericProperties &properties);
+    void preparePrerender(PrerenderedTexture &texture);
+    void finishPrerender(PrerenderedTexture &texture);
+    void renderPrerenderedTexture(PrerenderedTexture &texture, const GenericProperties &properties);
 
     void resize();
 

include/llmr/renderer/prerendered_texture.hpp

@@ -3,6 +3,7 @@
 
 #include <llmr/util/noncopyable.hpp>
 #include <llmr/platform/gl.hpp>
+#include <llmr/style/properties.hpp>
 
 namespace llmr {
 
@@ -10,7 +11,7 @@ class Painter;
 
 class PrerenderedTexture : private util::noncopyable {
 public:
-    PrerenderedTexture(uint16_t size);
+    PrerenderedTexture(const PrerenderProperties &properties);
     ~PrerenderedTexture();
 
     void bindTexture();
@@ -21,8 +22,10 @@ public:
 
     void blur(Painter& painter, uint16_t passes);
 
+public:
+    const PrerenderProperties properties;
+
 private:
-    const uint16_t size;
     GLint previous_fbo = 0;
     GLuint fbo = 0;
     GLuint texture = 0;

include/llmr/style/properties.hpp

@@ -93,10 +93,16 @@ struct GenericClass {
     boost::optional<TranslateAnchor> translateAnchor;
     boost::optional<FunctionProperty> opacity;
     boost::optional<PropertyTransition> opacity_transition;
-    boost::optional<bool> prerender;
-    boost::optional<float> prerenderBuffer;
-    boost::optional<uint16_t> prerenderSize;
-    boost::optional<uint16_t> prerenderBlur;
+    float prerender = false;
+    boost::optional<FunctionProperty> prerenderBuffer;
+    boost::optional<FunctionProperty> prerenderSize;
+    boost::optional<FunctionProperty> prerenderBlur;
+};
+
+struct PrerenderProperties {
+    float buffer = 1.0f / 32.0f;
+    uint16_t size = 256;
+    uint16_t blur = 0;
 };
 
 struct GenericProperties {
@@ -104,10 +110,21 @@ struct GenericProperties {
     std::array<float, 2> translate = {{ 0, 0 }};
     TranslateAnchor translateAnchor = TranslateAnchor::Map;
     float opacity = 1.0;
-    bool prerender = false;
-    float prerenderBuffer = 1.0f / 32.0f;
-    uint16_t prerenderSize = 256;
-    uint16_t prerenderBlur = 0;
+    bool prerender;
+
+    // These are unresolved properties because the value here is per tile, so it might differ.
+    boost::optional<FunctionProperty> prerenderBuffer;
+    boost::optional<FunctionProperty> prerenderSize;
+    boost::optional<FunctionProperty> prerenderBlur;
+
+    // Obtains prerender properties by integer zoom level.
+    inline PrerenderProperties getPrerenderProperties(int8_t z) const {
+        PrerenderProperties props;
+        if (prerenderBuffer) props.buffer = prerenderBuffer.get().evaluate<float>(z);
+        if (prerenderSize) props.size = prerenderSize.get().evaluate<uint16_t>(z);
+        if (prerenderBlur) props.blur = prerenderBlur.get().evaluate<uint16_t>(z);
+        return props;
+    }
 
     virtual bool isVisible() const {
         if (!enabled) { return false; }