Add style[] tag with button support

src/gui/StyleSpec.h

@@ -0,0 +1,102 @@
+/*
+Minetest
+Copyright (C) 2019 rubenwardy
+
+This program is free software; you can redistribute it and/or modify
+it under the terms of the GNU Lesser General Public License as published by
+the Free Software Foundation; either version 2.1 of the License, or
+(at your option) any later version.
+
+This program is distributed in the hope that it will be useful,
+but WITHOUT ANY WARRANTY; without even the implied warranty of
+MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+GNU Lesser General Public License for more details.
+
+You should have received a copy of the GNU Lesser General Public License along
+with this program; if not, write to the Free Software Foundation, Inc.,
+51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA.
+*/
+
+#include "irrlichttypes_extrabloated.h"
+
+#pragma once
+
+
+class StyleSpec
+{
+public:
+	enum Property {
+		NONE = 0,
+		TEXTCOLOR,
+		BGCOLOR,
+		NUM_PROPERTIES
+	};
+
+private:
+	std::unordered_map<Property, std::string> properties;
+
+public:
+	static Property GetPropertyByName(const std::string &name) {
+		if (name == "textcolor") {
+			return TEXTCOLOR;
+		} else if (name == "bgcolor") {
+			return BGCOLOR;
+		} else {
+			return NONE;
+		}
+	}
+
+	std::string get(Property prop, std::string def) const {
+		auto it = properties.find(prop);
+		if (it == properties.end()) {
+			return def;
+		}
+
+		return it->second;
+	}
+
+	void set(Property prop, std::string value) {
+		properties[prop] = std::move(value);
+	}
+
+	video::SColor getColor(Property prop, video::SColor def) const {
+		auto it = properties.find(prop);
+		if (it == properties.end()) {
+			return def;
+		}
+
+		parseColorString(it->second, def, false, 0xFF);
+		return def;
+	}
+
+	video::SColor getColor(Property prop) const {
+		auto it = properties.find(prop);
+		FATAL_ERROR_IF(it == properties.end(), "Unexpected missing property");
+
+		video::SColor color;
+		parseColorString(it->second, color, false, 0xFF);
+		return color;
+	}
+
+	bool hasProperty(Property prop) const {
+		return properties.find(prop) != properties.end();
+	}
+
+	StyleSpec &operator|=(const StyleSpec &other) {
+		for (size_t i = 1; i < NUM_PROPERTIES; i++) {
+			auto prop = (Property)i;
+			if (other.hasProperty(prop)) {
+				properties[prop] = other.get(prop, "");
+			}
+		}
+
+		return *this;
+	}
+
+	StyleSpec operator|(const StyleSpec &other) const {
+		StyleSpec newspec = *this;
+		newspec |= other;
+		return newspec;
+	}
+};
+