Allow air nodes to have a color.

As this comes with a significant performance penalty, this
feature must be enabled using the command-line option --drawair

For best results, the color of air should be fully transparent,
so that underlying nodes will override it.

Changelog

@@ -12,6 +12,12 @@
 		are: point, line, rectangle, ellipse (circle), text.
 		Translucency (alpha) is supported, although for ellipses, it does not
 		work as expected (due to a bug in libgd)
+	- 'air' nodes can now have a color. Their color should be defined as fully
+		transparent (alpha = 0), so that they don't obscure underlying blocks.
+		In that case, air will only be drawn if no other blocks are beneath it.
+		Nodes with alpha value 0 never participate in shading.
+		As this comes at a significant performance penalty, this feature is
+		subject to a command-line option: --drawair.
 	- A default color can be specified for invisible/undefined nodes in rendered
 		blocks Normally, such nodes are not drawn, so they have the background
 		color; If a different default color is specified, undefined/invisible

README.rst

@@ -171,6 +171,14 @@ draworigin:
 drawalpha:
     Allow blocks to be drawn with transparency, `--drawalpha`
 
+drawair:
+    Draw air blocks (at a significant performance penalty). `--drawair`
+
+    For best results, the air color should be defined as fully transparent
+    so that the color of underlying blocks overrides it.
+
+    This option has a significant performance impact.
+
 noshading:
     Don't draw shading on nodes, `--noshading`
 

TileGenerator.cpp

@@ -131,6 +131,7 @@ TileGenerator::TileGenerator():
 	m_drawPlayers(false),
 	m_drawScale(false),
 	m_drawAlpha(false),
+	m_drawAir(false),
 	m_shading(true),
 	m_border(0),
 	m_backend(DEFAULT_BACKEND),
@@ -268,6 +269,11 @@ void TileGenerator::setDrawAlpha(bool drawAlpha)
     m_drawAlpha = drawAlpha;
 }
 
+void TileGenerator::setDrawAir(bool drawAir)
+{
+	m_drawAir = drawAir;
+}
+
 void TileGenerator::setShading(bool shading)
 {
 	m_shading = shading;
@@ -1089,7 +1095,9 @@ void TileGenerator::processMapBlock(const DB::Block &block)
 			readString(name, data, dataOffset, nameLen, length);
 			name = name.c_str();		// Truncate any trailing NUL bytes
 			if (name == "air") {
-				m_blockAirId = nodeId;
+				ColorMap::const_iterator color = m_colors.find(name);
+				if (!m_drawAir || color == m_colors.end())
+					m_blockAirId = nodeId;
 			}
 			else if (name == "ignore") {
 				m_blockIgnoreId = nodeId;

TileGenerator.h

@@ -92,6 +92,7 @@ public:
 	void setDrawPlayers(bool drawPlayers);
 	void setDrawScale(bool drawScale);
 	void setDrawAlpha(bool drawAlpha);
+	void setDrawAir(bool drawAir);
 	void drawObject(const DrawObject &object) { m_drawObjects.push_back(object); }
 	void setShading(bool shading);
 	void setGeometry(const NodeCoord &corner1, const NodeCoord &corner2);
@@ -169,6 +170,7 @@ private:
 	bool m_drawPlayers;
 	bool m_drawScale;
 	bool m_drawAlpha;
+	bool m_drawAir;
 	bool m_shading;
 	int m_border;
 	std::string m_backend;

colors.txt

@@ -1,3 +1,4 @@
+air 220 220 255 0
 mesecons_pistons:piston_up_sticky_on 160 160 160
 mesecons_pistons:piston_normal_off 125 125 125
 mesecons_pistons:piston_up_pusher_sticky 123 124 124

mapper.cpp

@@ -26,6 +26,7 @@ using namespace std;
 #define OPT_PROGRESS_INDICATOR		0x82
 #define OPT_DRAW_OBJECT			0x83
 #define OPT_BLOCKCOLOR			0x84
+#define OPT_DRAWAIR			0x85
 #define OPT_VERBOSE_SEARCH_COLORS	0x86
 
 // Will be replaced with the actual name and location of the executable (if found)
@@ -71,6 +72,7 @@ void usage()
 			"  --drawplayers\n"
 			"  --draworigin\n"
 			"  --drawalpha\n"
+			"  --drawair\n"
 			"  --draw[map]point \"<x>,<y> color\"\n"
 			"  --draw[map]line \"<geometry> color\"\n"
 			"  --draw[map]circle \"<geometry> color\"\n"
@@ -526,6 +528,7 @@ int main(int argc, char *argv[])
 		{"drawplayers", no_argument, 0, 'P'},
 		{"drawscale", no_argument, 0, 'S'},
 		{"drawalpha", no_argument, 0, 'e'},
+		{"drawair", no_argument, 0, OPT_DRAWAIR},
 		{"drawpoint", required_argument, 0, OPT_DRAW_OBJECT},
 		{"drawline", required_argument, 0, OPT_DRAW_OBJECT},
 		{"drawcircle", required_argument, 0, OPT_DRAW_OBJECT},
@@ -647,6 +650,9 @@ int main(int argc, char *argv[])
 				case 'e':
 					generator.setDrawAlpha(true);
 					break;
+				case OPT_DRAWAIR:
+					generator.setDrawAir(true);
+					break;
 				case 'H':
 					generator.setShading(false);
 					break;