Wang Brush: Added line drawing with Shift modifier

As previously supported by the Terrain Brush, but now also supporting
the drawing of thinner lines in "Corner" and "Edge" modes.

Also make lines when moving fast with the mouse, to avoid gaps. This is
unfortunately not supported yet in "PaintEdgeAndCorner" mode.

src/tiled/geometry.cpp

@@ -169,8 +169,11 @@ QRegion ellipseRegion(int x0, int y0, int x1, int y1)
  * This is an implementation of Bresenham's line algorithm, initially copied
  * from http://en.wikipedia.org/wiki/Bresenham's_line_algorithm#Optimization
  * changed to C++ syntax.
+ *
+ * When the \a manhattan option (named after "Manhattan distance") is set to
+ * true, the points on the line can't take diagonal steps.
  */
-QVector<QPoint> pointsOnLine(int x0, int y0, int x1, int y1)
+QVector<QPoint> pointsOnLine(int x0, int y0, int x1, int y1, bool manhattan)
 {
     QVector<QPoint> ret;
 
@@ -197,15 +200,17 @@ QVector<QPoint> pointsOnLine(int x0, int y0, int x1, int y1)
     else
         ystep = -1;
 
-    for (int x = x0; x < x1 + 1 ; x++) {
-        if (steep)
-            ret += QPoint(y, x);
-        else
-            ret += QPoint(x, y);
+    ret.reserve(deltax + 1 + (manhattan ? deltay : 0));
+
+    for (int x = x0; x <= x1; x++) {
+        ret += steep ? QPoint(y, x) : QPoint(x, y);
         error = error - deltay;
         if (error < 0) {
              y = y + ystep;
              error = error + deltax;
+
+             if (manhattan && x < x1)
+                ret += steep ? QPoint(y, x) : QPoint(x, y);
         }
     }
 

src/tiled/geometry.h

@@ -28,13 +28,13 @@ namespace Tiled {
 
 QVector<QPoint> pointsOnEllipse(int x0, int y0, int x1, int y1);
 QRegion ellipseRegion(int x0, int y0, int x1, int y1);
-QVector<QPoint> pointsOnLine(int x0, int y0, int x1, int y1);
+QVector<QPoint> pointsOnLine(int x0, int y0, int x1, int y1, bool manhattan = false);
 
 inline QVector<QPoint> pointsOnEllipse(QPoint a, QPoint b)
 { return pointsOnEllipse(a.x(), a.y(), b.x(), b.y()); }
 
-inline QVector<QPoint> pointsOnLine(QPoint a, QPoint b)
-{ return pointsOnLine(a.x(), a.y(), b.x(), b.y()); }
+inline QVector<QPoint> pointsOnLine(QPoint a, QPoint b, bool manhattan = false)
+{ return pointsOnLine(a.x(), a.y(), b.x(), b.y(), manhattan); }
 
 QVector<QRegion> coherentRegions(const QRegion &region);