[core] Dynamic program compilation for data-driven properties

src/mbgl/programs/program_parameters.cpp

@@ -7,7 +7,7 @@ namespace mbgl {
 
 ProgramParameters::ProgramParameters(const float pixelRatio,
                                      const bool overdraw,
-                                     std::string cacheDir_)
+                                     optional<std::string> cacheDir_)
     : defines([&] {
           std::ostringstream ss;
           ss.imbue(std::locale("C"));
@@ -18,15 +18,31 @@ ProgramParameters::ProgramParameters(const float pixelRatio,
           }
           return ss.str();
       }()),
-      hash(std::hash<std::string>()(defines)),
       cacheDir(std::move(cacheDir_)) {
 }
 
-std::string ProgramParameters::cachePath(const char* name) const {
-    std::ostringstream ss;
-    ss << cacheDir << "/com.mapbox.gl.shader." << name << "." << std::setfill('0')
-       << std::setw(sizeof(size_t) * 2) << std::hex << hash << ".pbf";
-    return ss.str();
+const std::string& ProgramParameters::getDefines() const {
+    return defines;
+}
+
+optional<std::string> ProgramParameters::cachePath(const char* name) const {
+    if (!cacheDir) {
+        return {};
+    } else {
+        std::ostringstream ss;
+        ss << *cacheDir << "/com.mapbox.gl.shader." << name << "." << std::setfill('0')
+           << std::setw(sizeof(size_t) * 2) << std::hex << std::hash<std::string>()(defines) << ".pbf";
+        return ss.str();
+    }
+}
+
+ProgramParameters ProgramParameters::withAdditionalDefines(const std::vector<std::string>& additionalDefines) const {
+    ProgramParameters result(*this);
+    for (const auto& define : additionalDefines) {
+        result.defines += define;
+        result.defines += "\n";
+    }
+    return result;
 }
 
 } // namespace mbgl