--- a/viewport.h	Wed Jan 19 20:22:10 2005 +0000
+++ b/viewport.h	Wed Jan 19 20:55:23 2005 +0000
@@ -54,16 +54,39 @@
 	VPM_RAILDIRS = 3,
 	VPM_X_AND_Y = 4,
 	VPM_X_AND_Y_LIMITED = 5,
-	VPM_SIGNALDIRS = 6,
+	VPM_SIGNALDIRS = 6
+};
+
+// viewport highlight mode (for highlighting tiles below cursor)
+enum {
+	VHM_NONE = 0,    // default
+	VHM_RECT = 1,    // rectangle (stations, depots, ...)
+	VHM_POINT = 2,   // point (lower land, raise land, level land, ...)
+	VHM_SPECIAL = 3, // special mode used for highlighting while dragging (and for tunnels/docks)
+	VHM_DRAG = 4,    // dragging items in the depot windows
+	VHM_RAIL = 5,    // rail pieces
 };
 
 void VpSelectTilesWithMethod(int x, int y, int method);
 
+// highlighting draw styles
 enum {
 	HT_NONE = 0,
 	HT_RECT = 0x80,
 	HT_POINT = 0x40,
-	HT_LINE = 0x20,
+	HT_LINE = 0x20, /* used for autorail highlighting (longer streches)
+									 * (uses lower bits to indicate direction) */
+	HT_RAIL = 0x10, /* autorail (one piece)
+									 * (uses lower bits to indicate direction) */
+
+	/* lower bits (used with HT_LINE and HT_RAIL): 
+	 * (see ASCII art in autorail.h for a visual interpretation) */
+	HT_DIR_X = 0,  // X direction
+	HT_DIR_Y = 1,  // Y direction
+	HT_DIR_HU = 2, // horizontal upper
+	HT_DIR_HL = 3, // horizontal lower
+	HT_DIR_VL = 4, // vertical left
+	HT_DIR_VR = 5, // vertical right
 };
 
 typedef struct TileHighlightData {
@@ -81,9 +104,9 @@
 	byte dirty;
 	byte sizelimit;
 
-	byte drawstyle;
-	byte new_drawstyle;
-	byte next_drawstyle;
+	byte drawstyle;      // lower bits 0-3 are reserved for detailed highlight information information
+	byte new_drawstyle;  // only used in UpdateTileSelection() to as a buffer to compare if there was a change between old and new
+	byte next_drawstyle; // queued, but not yet drawn style
 
 	byte place_mode;
 	bool make_square_red;