Use highlight command to specify move legality

When a highlight command has been sent, LeftClick will only accept
to-square events when they occur on a square that highlight marked
as legal, i.e. indicated by a capital. The transparant 'color' T
is added to allow the engine to mark a to-square as legal without
putting any visible marker on it.

diff --git a/backend.c b/backend.c
index 15c3e42..b8ebf8f 100644 (file)
--- a/backend.c
+++ b/backend.c
@@ -269,6 +269,7 @@ char chatPartner[MAX_CHAT][MSG_SIZ]; /* [HGM] chat: list of chatting partners */
 extern int chatCount;
 int chattingPartner;
 char marker[BOARD_RANKS][BOARD_FILES]; /* [HGM] marks for target squares */
+char legal[BOARD_RANKS][BOARD_FILES];  /* [HGM] legal target squares */
 char lastMsg[MSG_SIZ];
 ChessSquare pieceSweep = EmptySquare;
 ChessSquare promoSweep = EmptySquare, defaultPromoChoice;
@@ -7019,12 +7020,15 @@ MarkByFEN(char *fen)
 {
        int r, f;
        if(!appData.markers || !appData.highlightDragging) return;
-       for(r=0; r<BOARD_HEIGHT; r++) for(f=BOARD_LEFT; f<BOARD_RGHT; f++) marker[r][f] = 0;
+       for(r=0; r<BOARD_HEIGHT; r++) for(f=BOARD_LEFT; f<BOARD_RGHT; f++) marker[r][f] = legal[r][f] = 0;
        r=BOARD_HEIGHT-1; f=BOARD_LEFT;
        while(*fen) {
            int s = 0;
            marker[r][f] = 0;
+           if(*fen >= 'A' && *fen <= 'Z') legal[r][f] = 1; else
+           if(*fen >= 'a' && *fen <= 'z') *fen += 'A' - 'a';
            if(*fen == '/' && f > BOARD_LEFT) f = BOARD_LEFT, r--; else
+           if(*fen == 'T') marker[r][f++] = 0; else
            if(*fen == 'Y') marker[r][f++] = 1; else
            if(*fen == 'R') marker[r][f++] = 2; else {
                while(*fen <= '9' && *fen >= '0') s = 10*s + *fen++ - '0';
@@ -7104,6 +7108,9 @@ CanPromote (ChessSquare piece, int y)
 void ReportClick(char *action, int x, int y)
 {
        char buf[MSG_SIZ]; // Inform engine of what user does
+       int r, f;
+       if(action[0] == 'l') // mark any target square of a lifted piece as legal to-square
+         for(r=0; r<BOARD_HEIGHT; r++) for(f=BOARD_LEFT; f<BOARD_RGHT; f++) legal[r][f] = 1;
        if(!first.highlight || gameMode == EditPosition) return;
        snprintf(buf, MSG_SIZ, "%s %c%d%s\n", action, x+AAA, y+ONE-'0', controlKey && action[0]=='p' ? "," : "");
        SendToProgram(buf, &first);
@@ -7321,6 +7328,13 @@ LeftClick (ClickType clickType, int xPix, int yPix)
 
     clearFlag = 0;
 
+    if(gameMode != EditPosition && !appData.testLegality && !legal[y][x]) {
+       if(dragging) DragPieceEnd(xPix, yPix), dragging = 0;
+       DisplayMessage(_("only marked squares are legal"),"");
+       DrawPosition(TRUE, NULL);
+       return; // ignore to-click
+    }
+
     /* we now have a different from- and (possibly off-board) to-square */
     /* Completed move */
     if(!sweepSelecting) {