Use in-place sweep-selection for click-click under-promotion

With detour under-promotion a piece cycles through all possible choices
during backwards dragging. But in a click-click move there is no dragging.
This used to be solved by letting the second click start a drag event of
the default promotion choice, which you could accept by immediately
releasing the mouse button, or drag around to change it first.
 The dragging in this case seemed a little unnatural, because the to-square
was already indicated by the down-click. So it has been changed now to the
promo choice appearing on the down-clicked to-square, followed by
EditPosition-like sweep-selection on that square when one wants to under-
promote. The move is always accepted no matter where the up-click takes
place, except when it takes place on the from-square (which offers a last-
resort abort possibiliy).
 Note that click-click promotion is essential in variants where it is not
obvious from the from-square alone that a promotion is imminent, but where
it depends on the to-square. (Such as Shogi.) There drag-drop detour under-
promotion is not possible.

diff --git a/backend.c b/backend.c
index 9ac6a58..265a55c 100644 (file)
--- a/backend.c
+++ b/backend.c
@@ -5173,6 +5173,12 @@ Sweep (int step)
     } while(PieceToChar(promoSweep) == '.' || PieceToChar(promoSweep) == '~' || promoSweep == pawn ||
            appData.testLegality && (promoSweep == king ||
            gameInfo.variant == VariantShogi && promoSweep != PROMOTED last && last != PROMOTED promoSweep && last != promoSweep));
+    if(toX >= 0) {
+       int victim = boards[currentMove][toY][toX];
+       boards[currentMove][toY][toX] = promoSweep;
+       DrawPosition(FALSE, boards[currentMove]);
+       boards[currentMove][toY][toX] = victim;
+    } else
     ChangeDragPiece(promoSweep);
 }
 
@@ -6971,7 +6977,7 @@ LeftClick (ClickType clickType, int xPix, int yPix)
 {
     int x, y;
     Boolean saveAnimate;
-    static int second = 0, promotionChoice = 0, clearFlag = 0;
+    static int second = 0, promotionChoice = 0, clearFlag = 0, sweepSelecting = 0;
     char promoChoice = NULLCHAR;
     ChessSquare piece;
     static TimeMark lastClickTime, prevClickTime;
@@ -6995,7 +7001,7 @@ LeftClick (ClickType clickType, int xPix, int yPix)
        defaultPromoChoice = promoSweep;
        promoSweep = EmptySquare;   // terminate sweep
        promoDefaultAltered = TRUE;
-       if(!selectFlag && (x != toX || y != toY)) x = fromX, y = fromY; // and fake up-click on same square if we were still selecting
+       if(!selectFlag && !sweepSelecting && (x != toX || y != toY)) x = fromX, y = fromY; // and fake up-click on same square if we were still selecting
     }
 
     if(promotionChoice) { // we are waiting for a click to indicate promotion piece
@@ -7154,9 +7160,10 @@ LeftClick (ClickType clickType, int xPix, int yPix)
            /* Undo animation damage if any */
            DrawPosition(FALSE, NULL);
        }
-       if (second) {
+       if (second || sweepSelecting) {
            /* Second up/down in same square; just abort move */
-           second = 0;
+           if(sweepSelecting) DrawPosition(FALSE, boards[currentMove]);
+           second = sweepSelecting = 0;
            fromX = fromY = -1;
            gatingPiece = EmptySquare;
            ClearHighlights();
@@ -7173,9 +7180,12 @@ LeftClick (ClickType clickType, int xPix, int yPix)
 
     /* we now have a different from- and (possibly off-board) to-square */
     /* Completed move */
-    toX = x;
-    toY = y;
-    saveAnimate = appData.animate;
+    if(!sweepSelecting) {
+       toX = x;
+       toY = y;
+       saveAnimate = appData.animate;
+    } else sweepSelecting = 0; // this must be the up-click corresponding to the down-click that started the sweep
+
     if (clickType == Press) {
        if(gameMode == EditPosition && boards[currentMove][fromY][fromX] == EmptySquare) {
            // must be Edit Position mode with empty-square selected
@@ -7186,16 +7196,13 @@ LeftClick (ClickType clickType, int xPix, int yPix)
        if(HasPromotionChoice(fromX, fromY, toX, toY, &promoChoice, FALSE)) {
          if(appData.sweepSelect) {
            ChessSquare piece = boards[currentMove][fromY][fromX];
-           ChessSquare victim = boards[currentMove][toY][toX];
-           boards[currentMove][toY][toX] = piece; // kludge: make sure there is something to grab for drag
-           DragPieceBegin(xPix, yPix, TRUE); dragging = 1;
-           boards[currentMove][toY][toX] = victim;
            promoSweep = defaultPromoChoice;
            if(PieceToChar(PROMOTED piece) == '+') promoSweep = PROMOTED piece;
            selectFlag = 0; lastX = xPix; lastY = yPix;
            Sweep(0); // Pawn that is going to promote: preview promotion piece
+           sweepSelecting = 1;
            DisplayMessage("", _("Pull pawn backwards to under-promote"));
-           DrawPosition(FALSE, boards[currentMove]);
+           MarkTargetSquares(1);
          }
          return; // promo popup appears on up-click
        }