diff -aur ./common.h xboard-4.2.7/common.h
--- ./common.h	2003-10-28 05:21:00.000000000 +1000
+++ xboard-4.2.7/common.h	2004-02-06 01:48:08.000000000 +1000
@@ -130,6 +130,7 @@
 #define DARK_SQUARE_COLOR	"#77A26D"
 #define JAIL_SQUARE_COLOR       "#808080"
 #define HIGHLIGHT_SQUARE_COLOR	"#FFFF00"
+#define MOVE_SQUARE_COLOR	    "#4C00FF"
 #define PREMOVE_HIGHLIGHT_COLOR	"#FF0000"
 #define BELLCHAR                '\007'
 #define NULLCHAR                '\000'
@@ -265,6 +266,7 @@
     char *darkSquareColor;
     char *jailSquareColor;
     char *highlightSquareColor;
+    char *moveSquareColor;
     char *premoveHighlightColor;
 #else
     int whitePieceColor;
@@ -273,6 +275,7 @@
     int darkSquareColor;
     int jailSquareColor;
     int highlightSquareColor;
+    int moveSquareColor;
     int premoveHighlightColor;
 #endif
     int movesPerSession;
@@ -424,6 +427,7 @@
     char *zippyVariants;
     int zippyMaxGames;
     int zippyReplayTimeout; /*seconds*/
+	Boolean showLegalMoves;
 #endif
 } AppData, *AppDataPtr;
 
diff -aur ./xboard.c xboard-4.2.7/xboard.c
--- ./xboard.c	2003-11-19 18:42:18.000000000 +1000
+++ xboard-4.2.7/xboard.c	2004-02-06 01:52:45.000000000 +1000
@@ -185,6 +185,7 @@
 #include "common.h"
 #include "frontend.h"
 #include "backend.h"
+#include "backendz.h"
 #include "moves.h"
 #include "xboard.h"
 #include "childio.h"
@@ -385,6 +386,8 @@
 			 Cardinal *nprms));
 void TestLegalityProc P((Widget w, XEvent *event, String *prms,
 			  Cardinal *nprms));
+void ShowLegalMovesProc P((Widget w, XEvent *event, String *prms,
+			  Cardinal *nprms));
 void InfoProc P((Widget w, XEvent *event, String *prms, Cardinal *nprms));
 void ManProc P((Widget w, XEvent *event, String *prms, Cardinal *nprms));
 void HintProc P((Widget w, XEvent *event, String *prms, Cardinal *nprms));
@@ -408,6 +411,9 @@
 static void DrawDragPiece P((void));
 char *ModeToWidgetName P((GameMode mode));
 
+static void ShowLegalPieceSquares(int boardX,int boardY);
+static void UnShowLegalPieceSquares();
+
 /*
 * XBoard depends on Xt R4 or higher
 */
@@ -417,9 +423,9 @@
 Display *xDisplay;
 Window xBoardWindow;
 Pixel lightSquareColor, darkSquareColor, whitePieceColor, blackPieceColor,
-  jailSquareColor, highlightSquareColor, premoveHighlightColor;
+  jailSquareColor, highlightSquareColor, moveSquareColor, premoveHighlightColor;
 GC lightSquareGC, darkSquareGC, jailSquareGC, lineGC, wdPieceGC, wlPieceGC,
-  bdPieceGC, blPieceGC, wbPieceGC, bwPieceGC, coordGC, highlineGC,
+  bdPieceGC, blPieceGC, wbPieceGC, bwPieceGC, coordGC, highlineGC, 
   wjPieceGC, bjPieceGC, prelineGC;
 Pixmap iconPixmap, wIconPixmap, bIconPixmap, xMarkPixmap;
 Widget shellWidget, layoutWidget, formWidget, boardWidget, messageWidget, 
@@ -605,6 +611,7 @@
     {"Show Coords", ShowCoordsProc},
     {"Show Thinking", ShowThinkingProc},
     {"Test Legality", TestLegalityProc},
+	{"Show Legal Moves",ShowLegalMovesProc},
     {NULL, NULL}
 };
 
@@ -739,6 +746,9 @@
     { "highlightSquareColor", "highlightSquareColor", XtRString,
 	sizeof(String),	XtOffset(AppDataPtr, highlightSquareColor),
 	XtRString, HIGHLIGHT_SQUARE_COLOR },
+    { "moveSquareColor", "moveSquareColor", XtRString,
+	sizeof(String),	XtOffset(AppDataPtr, moveSquareColor),
+	XtRString, MOVE_SQUARE_COLOR },
     { "premoveHighlightColor", "premoveHighlightColor", XtRString,
 	sizeof(String),	XtOffset(AppDataPtr, premoveHighlightColor),
 	XtRString, PREMOVE_HIGHLIGHT_COLOR },
@@ -1144,6 +1154,7 @@
     { "-lightSquareColor", "lightSquareColor", XrmoptionSepArg, NULL },
     { "-darkSquareColor", "darkSquareColor", XrmoptionSepArg, NULL },
     { "-highlightSquareColor", "highlightSquareColor", XrmoptionSepArg, NULL },
+    { "-moveSquareColor", "moveSquareColor", XrmoptionSepArg, NULL },
     { "-premoveHighlightColor", "premoveHighlightColor", XrmoptionSepArg,NULL},
     { "-movesPerSession", "movesPerSession", XrmoptionSepArg, NULL },
     { "-mps", "movesPerSession", XrmoptionSepArg, NULL },
@@ -1522,6 +1533,7 @@
     { "ShowCoordsProc", ShowCoordsProc },
     { "ShowThinkingProc", ShowThinkingProc },
     { "TestLegalityProc", TestLegalityProc },
+    { "ShowLegalMovesProc", ShowLegalMovesProc },
     { "InfoProc", InfoProc },
     { "ManProc", ManProc },
     { "HintProc", HintProc },
@@ -2068,6 +2080,18 @@
     }
 
     if (!appData.monoMode) {
+	vFrom.addr = (caddr_t) appData.moveSquareColor;
+	vFrom.size = strlen(appData.moveSquareColor);
+	XtConvert(shellWidget, XtRString, &vFrom, XtRPixel, &vTo);
+	if (vTo.addr == NULL) {
+	  appData.monoMode = True;
+	  forceMono = True;
+	} else {
+	  moveSquareColor = *(Pixel *) vTo.addr;
+	}
+    }
+
+    if (!appData.monoMode) {
 	vFrom.addr = (caddr_t) appData.premoveHighlightColor;
 	vFrom.size = strlen(appData.premoveHighlightColor);
 	XtConvert(shellWidget, XtRString, &vFrom, XtRPixel, &vTo);
@@ -6264,6 +6288,25 @@
     DrawPosition(True, NULL);
 }
 
+/* show legal moves on board when moving/dragging a piece */
+void ShowLegalMovesProc(w, event, prms, nprms)
+     Widget w;
+     XEvent *event;
+     String *prms;
+     Cardinal *nprms;
+{
+    Arg args[16];
+	appData.showLegalMoves = !appData.showLegalMoves;
+
+    if (appData.showLegalMoves) {
+	XtSetArg(args[0], XtNleftBitmap, xMarkPixmap);
+    } else {
+	XtSetArg(args[0], XtNleftBitmap, None);
+    }
+    XtSetValues(XtNameToWidget(menuBarWidget, "menuOptions.Show Legal Moves"),
+		args, 1);
+}
+
 void TestLegalityProc(w, event, prms, nprms)
      Widget w;
      XEvent *event;
@@ -8361,11 +8404,13 @@
   damage[toY][toX] = True;
 }
 
+
 static void
 DragPieceBegin(x, y)
      int x; int y;
 {
-    int	 boardX, boardY, color;
+
+	int boardX, boardY, color;
     XPoint corner;
 
     /* Are we animating? */
@@ -8399,6 +8444,10 @@
     if (player.dragPiece >= 0 && player.dragPiece < EmptySquare) {
 	player.dragActive = True;
 	BeginAnimation(&player, player.dragPiece, color, &corner);
+
+	/* show the squares where this piece can be legally moved */
+	ShowLegalPieceSquares(fromX,fromY);
+
 	/* Mark this square as needing to be redrawn. Note that
 	   we don't remove the piece though, since logically (ie
 	   as seen by opponent) the move hasn't been made yet. */
@@ -8408,6 +8457,94 @@
     }
 }
 
+/* squares that are highlighted from moving a piece */
+static int xHighlights[BOARD_SIZE*BOARD_SIZE];
+static int yHighlights[BOARD_SIZE*BOARD_SIZE];
+
+/* highlight squares where legal moves can be made by current piece */
+static void ShowLegalPieceSquares(boardX,boardY)
+	int boardX;int boardY;
+{
+
+    int	 x, y, currHighlight = 0, i = 0;
+
+	if ( ! appData.showLegalMoves ) return;
+
+	for ( i = 0 ; i < BOARD_SIZE; i++ )
+	{
+		xHighlights[i] = -1;
+		yHighlights[i] = -1;
+	}
+	
+	for ( x = 0; x < BOARD_SIZE ; x++)
+	{
+		for ( y = 0 ; y < BOARD_SIZE; y++)
+		{
+			int legalmove = LegalityTest(boards[currentMove],
+										 PosFlags(currentMove),
+										 EP_UNKNOWN, fromY, fromX, y,x,0);
+#ifdef DEBUG_MOVE_PIECES
+			printf("Move from %d %d to %d %d == %s - currentMove = %d\n",boardX,boardY,x,y,(legalmove == IllegalMove || legalmove == ImpossibleMove)?"Illegal move":"Legal move",currentMove);
+
+#endif
+
+			if ( legalmove != IllegalMove && legalmove != ImpossibleMove)
+			{
+				GC movepieceGC;
+				XtGCMask value_mask = GCLineWidth | GCLineStyle | GCForeground
+									| GCBackground | GCFunction | GCPlaneMask;
+				XGCValues gc_values;
+				gc_values.plane_mask = AllPlanes;
+				gc_values.line_width = lineGap;
+				gc_values.line_style = LineSolid;
+				gc_values.function = GXcopy;
+
+#ifdef DEBUG_MOVE_PIECES
+				printf("Highlight x = %d y = %d\n",x,y);
+#endif
+				gc_values.foreground = moveSquareColor;
+				gc_values.background = moveSquareColor;
+
+				drawHighlight(x,y,XtGetGC(shellWidget, value_mask, &gc_values));
+				xHighlights[currHighlight] = x;
+				yHighlights[currHighlight] = y;
+				currHighlight++;
+			}
+		}
+	}
+}
+
+/* remove highlights from squares that were highlighted
+   as a result of picking up a piece and showing the legal moves */
+static void UnShowLegalPieceSquares()
+{
+	int i = 0, boardX, boardY, color;
+	GC clearpieceGC;
+	XtGCMask value_mask = GCLineWidth | GCLineStyle | GCForeground
+									| GCBackground | GCFunction | GCPlaneMask;
+	XGCValues gc_values;
+	if ( ! appData.showLegalMoves ) return;
+
+	gc_values.plane_mask = AllPlanes;
+	gc_values.line_width = lineGap;
+	gc_values.line_style = LineSolid;
+	gc_values.function = GXcopy;
+
+	gc_values.foreground = jailSquareColor;
+	gc_values.background = jailSquareColor;
+
+	for ( i = 0 ; i < BOARD_SIZE*BOARD_SIZE && xHighlights[i] != -1 && yHighlights[i] != -1; i++ )
+	{
+		clearpieceGC = XtGetGC(shellWidget, value_mask, &gc_values);	
+#ifdef DEBUG_MOVE_PIECES
+		printf("Erasing %d %d\n",BOARD_SIZE*BOARD_SIZE,xHighlights[i],yHighlights[i]);
+#endif
+		drawHighlight(xHighlights[i], yHighlights[i],clearpieceGC);
+		xHighlights[i] = -1;
+		yHighlights[i] = -1;
+	}
+}
+
 static void
 DragPieceMove(x, y)
      int x; int y;
@@ -8427,10 +8564,11 @@
     corner.y = y - player.mouseDelta.y;
     AnimationFrame(&player, &corner, player.dragPiece);
 #if HIGHDRAG
-    if (appData.highlightDragging) {
-	int boardX, boardY;
-	BoardSquare(x, y, &boardX, &boardY);
-	SetHighlights(fromX, fromY, boardX, boardY);
+    if (appData.highlightDragging) 
+	{
+			int boardX, boardY;
+			BoardSquare(x, y, &boardX, &boardY);
+			SetHighlights(fromX, fromY, boardX, boardY);
     }
 #endif
 }
@@ -8439,7 +8577,8 @@
 DragPieceEnd(x, y)
      int x; int y;
 {
-    int boardX, boardY, color;
+	int boardX, boardY, color;
+
     XPoint corner;
 
     /* Are we animating? */
@@ -8461,6 +8600,9 @@
     /* This prevents weird things happening with fast successive
        clicks which on my Sun at least can cause motion events
        without corresponding press/release. */
+
+	/* un highlight the squares where the piece can be legally moved */
+	UnShowLegalPieceSquares();
     player.dragActive = False;
 }
 
Only in .: xboard.txt
Only in .: zic2xpm.txt