Disabled placement of empty tiles by Stamp Brush in Terrain Fill mode

Also exposed the new TileLayerWangEdit.erasingEnabled property in the
scripting API.

Another change is that empty tiles no longer contribute to the desired
WangId for the Terrain Fill mode (when corrections are disabled).
Previously, only tiles outside of the map would not contribute to the
desired WangId. This change yields nicer behavior when using the Wang
Fill mode with the Stamp Brush, but it may need to be reconsidered for
the Shape Fill tool or a later Terrain Fill tool.

docs/scripting-doc/index.d.ts

@@ -2965,6 +2965,12 @@ interface TileLayerWangEdit {
    */
   correctionsEnabled : boolean
 
+  /**
+   * Whether the empty tile is considered when looking for matching tiles.
+   * Defaults to `true`.
+   */
+  erasingEnabled : boolean
+
   /**
    * Sets the desired color for the given Wang index at the given location.
    *

src/tiled/stampbrush.cpp

@@ -462,6 +462,7 @@ void StampBrush::drawPreviewLayer(const QVector<QPoint> &points)
         };
 
         WangFiller wangFiller(*mWangSet, *tileLayer, mapDocument()->renderer());
+        wangFiller.setErasingEnabled(false);
         wangFiller.setRegion(paintedRegion);
         wangFiller.apply(*previewLayer);
 

src/tiled/tilelayerwangedit.cpp

@@ -26,6 +26,7 @@
 #include "maprenderer.h"
 #include "scriptmanager.h"
 #include "tilelayer.h"
+#include "wangfiller.h"
 
 #include <QCoreApplication>
 
@@ -63,6 +64,16 @@ void TileLayerWangEdit::setCorrectionsEnabled(bool correctionsEnabled)
     mWangFiller->setCorrectionsEnabled(correctionsEnabled);
 }
 
+bool TileLayerWangEdit::erasingEnabled() const
+{
+    return mWangFiller->erasingEnabled();
+}
+
+void TileLayerWangEdit::setErasingEnabled(bool erasingEnabled)
+{
+    mWangFiller->setErasingEnabled(erasingEnabled);
+}
+
 void TileLayerWangEdit::setWangIndex(QPoint pos, WangIndex::Value index, int color)
 {
     mWangFiller->setWangIndex(pos, static_cast<WangId::Index>(index), color);

src/tiled/tilelayerwangedit.h

@@ -23,7 +23,6 @@
 
 #include "editablewangset.h"
 #include "map.h"
-#include "wangfiller.h"
 
 #include <QObject>
 
@@ -32,6 +31,8 @@
 namespace Tiled {
 
 class EditableTileLayer;
+class MapRenderer;
+class WangFiller;
 
 // Copy of WangId::Index, for exposing the enum to JS
 namespace WangIndex
@@ -63,6 +64,7 @@ class TileLayerWangEdit : public QObject
     Q_PROPERTY(Tiled::EditableWangSet *wangSet READ wangSet CONSTANT)
     Q_PROPERTY(bool mergeable READ isMergeable WRITE setMergeable)
     Q_PROPERTY(bool correctionsEnabled READ correctionsEnabled WRITE setCorrectionsEnabled)
+    Q_PROPERTY(bool erasingEnabled READ erasingEnabled WRITE setErasingEnabled)
 
 public:
     explicit TileLayerWangEdit(EditableTileLayer *tileLayer,
@@ -80,7 +82,10 @@ class TileLayerWangEdit : public QObject
     bool isMergeable() const;
 
     bool correctionsEnabled() const;
-    void setCorrectionsEnabled(bool newCorrectionsEnabled);
+    void setCorrectionsEnabled(bool correctionsEnabled);
+
+    bool erasingEnabled() const;
+    void setErasingEnabled(bool erasingEnabled);
 
     EditableTileLayer *target() const;
     EditableWangSet *wangSet() const;

src/tiled/wangfiller.cpp

@@ -336,13 +336,14 @@ WangId WangFiller::wangIdFromSurroundings(QPoint point) const
     for (int i = 0; i < WangId::NumIndexes; ++i) {
         wangIds[i] = WangId::FULL_MASK;
 
-        if (!mMapRenderer->map()->infinite() && !mBack.rect().contains(adjacentPoints[i]))
+        const auto &cell = mBack.cellAt(adjacentPoints[i]);
+        if (cell.isEmpty())
             continue;
 
         if (mFillRegion.region.contains(adjacentPoints[i]))
             continue;
 
-        wangIds[i] = mWangSet.wangIdOfCell(mBack.cellAt(adjacentPoints[i]));
+        wangIds[i] = mWangSet.wangIdOfCell(cell);
     }
 
     return wangIdFromSurrounding(wangIds);
@@ -410,7 +411,8 @@ bool WangFiller::findBestMatch(const TileLayer &target,
     for (int i = 0, i_end = wangIdsAndCells.size(); i < i_end; ++i)
         processCandidate(wangIdsAndCells[i].wangId, wangIdsAndCells[i].cell);
 
-    processCandidate(WangId(), Cell());
+    if (mErasingEnabled)
+        processCandidate(WangId(), Cell());
 
     // Choose a candidate at random, with consideration for probability
     while (!matches.isEmpty()) {

src/tiled/wangfiller.h

@@ -73,6 +73,9 @@ class WangFiller
     bool correctionsEnabled() const { return mCorrectionsEnabled; }
     void setCorrectionsEnabled(bool enabled) { mCorrectionsEnabled = enabled; }
 
+    bool erasingEnabled() const { return mErasingEnabled; }
+    void setErasingEnabled(bool enabled) { mErasingEnabled = enabled; }
+
     void setDebugPainter(QPainter *painter) { mDebugPainter = painter; }
 
     void setRegion(const QRegion &region);
@@ -104,6 +107,7 @@ class WangFiller
     const MapRenderer * const mMapRenderer;
     const HexagonalRenderer * const mHexagonalRenderer;
     bool mCorrectionsEnabled = false;
+    bool mErasingEnabled = true;
     FillRegion mFillRegion;
 
     QPainter *mDebugPainter = nullptr;