Add a flag to never output empty images.

README.rst

@@ -83,6 +83,9 @@ extent:
 noshading:
     Don't draw shading on nodes, ``--noshading``
 
+noemptyimage:
+    Don't output anything when the image would be empty, ``--noemptyimage``
+
 min-y:
     Don't draw nodes below this y value, e.g. ``--min-y -25``
 

TileGenerator.cpp

@@ -79,6 +79,7 @@ TileGenerator::TileGenerator():
 	m_drawScale(false),
 	m_drawAlpha(false),
 	m_shading(true),
+	m_dontWriteEmpty(false),
 	m_backend(""),
 	m_xBorder(0),
 	m_yBorder(0),
@@ -228,6 +229,10 @@ void TileGenerator::printGeometry(const std::string &input)
 
 }
 
+void TileGenerator::setDontWriteEmpty(bool f)
+{
+	m_dontWriteEmpty = f;
+}
 
 void TileGenerator::generate(const std::string &input, const std::string &output)
 {
@@ -238,6 +243,13 @@ void TileGenerator::generate(const std::string &input, const std::string &output
 
 	openDb(input_path);
 	loadBlocks();
+
+	if (m_dontWriteEmpty  && ! m_positions.size())
+	{
+		closeDatabase();
+		return;
+	}
+
 	createImage();
 	renderMap();
 	closeDatabase();

include/TileGenerator.h

@@ -89,6 +89,7 @@ public:
 	void printGeometry(const std::string &input);
 	void setZoom(int zoom);
 	void setScales(uint flags);
+	void setDontWriteEmpty(bool f);
 
 private:
 	void parseColorsStream(std::istream &in);
@@ -120,6 +121,7 @@ private:
 	bool m_drawScale;
 	bool m_drawAlpha;
 	bool m_shading;
+	bool m_dontWriteEmpty;
 	std::string m_backend;
 	int m_xBorder, m_yBorder;
 

mapper.cpp

@@ -24,6 +24,7 @@ void usage()
 			"  --draworigin\n"
 			"  --drawalpha\n"
 			"  --noshading\n"
+			"  --noemptyimage\n"
 			"  --min-y <y>\n"
 			"  --max-y <y>\n"
 			"  --backend <backend>\n"
@@ -87,6 +88,7 @@ int main(int argc, char *argv[])
 		{"zoom", required_argument, 0, 'z'},
 		{"colors", required_argument, 0, 'C'},
 		{"scales", required_argument, 0, 'f'},
+		{"noemptyimage", no_argument, 0, 'n'},
 		{0, 0, 0, 0}
 	};
 
@@ -195,6 +197,9 @@ int main(int argc, char *argv[])
 			case 'C':
 				colors = optarg;
 				break;
+			case 'n':
+				generator.setDontWriteEmpty(true);
+				break;
 			default:
 				exit(1);
 		}

minetestmapper.6

@@ -56,6 +56,10 @@ Allow nodes to be drawn with transparency
 .BR \-\-noshading
 Don't draw shading on nodes
 
+.TP
+.BR \-\-noemptyimage
+Don't output anything when the image would be empty.
+
 .TP
 .BR \-\-min-y " " \fInumber\fR
 Don't draw nodes below this y value, e.g. "--min-y -25"