Re-add --backend to allow overriding auto-detected backend

TileGenerator.cpp

@@ -96,6 +96,7 @@ TileGenerator::TileGenerator():
 	m_drawScale(false),
 	m_drawAlpha(false),
 	m_shading(true),
+	m_backend(""),
 	m_border(0),
 	m_image(0),
 	m_xMin(INT_MAX),
@@ -181,6 +182,11 @@ void TileGenerator::setShading(bool shading)
 	m_shading = shading;
 }
 
+void TileGenerator::setBackend(std::string backend)
+{
+	m_backend = backend;
+}
+
 void TileGenerator::setGeometry(int x, int y, int w, int h)
 {
 	if (x > 0) {
@@ -284,11 +290,14 @@ void TileGenerator::parseColorsStream(std::istream &in)
 
 void TileGenerator::openDb(const std::string &input)
 {
-	std::ifstream ifs((input + "/world.mt").c_str());
-	if(!ifs.good())
-		throw std::runtime_error("Failed to read world.mt");
-	std::string backend = get_setting("backend", ifs);
-	ifs.close();
+	std::string backend = m_backend;
+	if(backend == "") {
+		std::ifstream ifs((input + "/world.mt").c_str());
+		if(!ifs.good())
+			throw std::runtime_error("Failed to read world.mt");
+		backend = get_setting("backend", ifs);
+		ifs.close();
+	}
 
 	if(backend == "sqlite3")
 		m_db = new DBSQLite3(input);

TileGenerator.h

@@ -86,6 +86,7 @@ private:
 	bool m_drawScale;
 	bool m_drawAlpha;
 	bool m_shading;
+	std::string m_backend;
 	int m_border;
 
 	DB *m_db;

mapper.cpp

@@ -34,6 +34,7 @@ void usage()
 			"  --noshading\n"
 			"  --min-y <y>\n"
 			"  --max-y <y>\n"
+			"  --backend <backend>\n"
 			"  --geometry x:y+w+h\n"
 			"Color format: '#000000'\n";
 	std::cout << usage_text;
@@ -55,6 +56,7 @@ int main(int argc, char *argv[])
 		{"drawscale", no_argument, 0, 'S'},
 		{"drawalpha", no_argument, 0, 'e'},
 		{"noshading", no_argument, 0, 'H'},
+		{"backend", required_argument, 0, 'd'},
 		{"geometry", required_argument, 0, 'g'},
 		{"min-y", required_argument, 0, 'a'},
 		{"max-y", required_argument, 0, 'c'}
@@ -109,11 +111,14 @@ int main(int argc, char *argv[])
 				generator.setDrawScale(true);
 				break;
 			case 'e':
-			    generator.setDrawAlpha(true);
-			    break;
+				generator.setDrawAlpha(true);
+				break;
 			case 'H':
 				generator.setShading(false);
 				break;
+			case 'd':
+				generator.setBackend(optarg);
+				break;
 			case 'a': {
 					istringstream iss;
 					iss.str(optarg);