Fix "Straight Line from Last Point” bug in Tilemaps (fix #4623)

Prior to this fix, when the following conditions were met:
- On a tilemap layer
- Tilemap mode = OFF
- Tool = Pencil
- Tileset mode = Manual
- Modifying an existing tile with the "quick line"
  (i.e. holding down the SHIFT key)
resulted in incorrect tool behavior.

src/app/tools/intertwiners.h

@@ -1,5 +1,5 @@
 // Aseprite
-// Copyright (C) 2018-2024  Igara Studio S.A.
+// Copyright (C) 2018-2025  Igara Studio S.A.
 // Copyright (C) 2001-2018  David Capello
 //
 // This program is distributed under the terms of
@@ -74,12 +74,6 @@ public:
 };
 
 class IntertwineAsLines : public Intertwine {
-  // It was introduced to know if joinStroke function
-  // was executed inmediatelly after a "Last" trace policy (i.e. after the
-  // user confirms a line draw while he is holding down the SHIFT key), so
-  // we have to ignore printing the first pixel of the line.
-  bool m_retainedTracePolicyLast = false;
-
   // In freehand-like tools, on each mouse movement we draw only the
   // line between the last two mouse points in the stroke (the
   // complete stroke is not re-painted again), so we want to indicate
@@ -90,22 +84,10 @@ class IntertwineAsLines : public Intertwine {
 public:
   bool snapByAngle() override { return true; }
 
-  void prepareIntertwine(ToolLoop* loop) override
-  {
-    m_retainedTracePolicyLast = false;
-    m_firstStroke = true;
-  }
+  void prepareIntertwine(ToolLoop* loop) override { m_firstStroke = true; }
 
   void joinStroke(ToolLoop* loop, const Stroke& stroke) override
   {
-    // Required for LineFreehand controller in the first stage, when
-    // we are drawing the line and the trace policy is "Last". Each
-    // new joinStroke() is like a fresh start.  Without this fix, the
-    // first stage on LineFreehand will draw a "star" like pattern
-    // with lines from the first point to the last point.
-    if (loop->getTracePolicy() == TracePolicy::Last)
-      m_retainedTracePolicyLast = true;
-
     if (stroke.size() == 0)
       return;
     else if (stroke.size() == 1) {
@@ -129,9 +111,10 @@ public:
       // when we use Shift+click in the Pencil tool to continue the
       // old stroke).
       // TODO useful only in the case when brush size = 1px
-      const int start =
-        (loop->getController()->isFreehand() && (m_retainedTracePolicyLast || !m_firstStroke) ? 1 :
-                                                                                                0);
+      const int start = (loop->getController()->isFreehand() &&
+                             ((loop->getTracePolicy() == TracePolicy::Last) || !m_firstStroke) ?
+                           1 :
+                           0);
 
       for (int c = start; c < pts.size(); ++c)
         doPointshapeStrokePt(pts[c], loop);
@@ -442,11 +425,6 @@ public:
 };
 
 class IntertwineAsPixelPerfect : public Intertwine {
-  // It was introduced to know if joinStroke function
-  // was executed inmediatelly after a "Last" trace policy (i.e. after the
-  // user confirms a line draw while he is holding down the SHIFT key), so
-  // we have to ignore printing the first pixel of the line.
-  bool m_retainedTracePolicyLast = false;
   Stroke m_pts;
   bool m_saveStrokeArea = false;
 
@@ -483,7 +461,6 @@ public:
   void prepareIntertwine(ToolLoop* loop) override
   {
     m_pts.reset();
-    m_retainedTracePolicyLast = false;
     m_grid = m_dstGrid = m_celGrid = loop->getGrid();
     m_restoredRegion.clear();
 
@@ -509,10 +486,8 @@ public:
     // new joinStroke() is like a fresh start.  Without this fix, the
     // first stage on LineFreehand will draw a "star" like pattern
     // with lines from the first point to the last point.
-    if (loop->getTracePolicy() == TracePolicy::Last) {
-      m_retainedTracePolicyLast = true;
+    if (loop->getTracePolicy() == TracePolicy::Last)
       m_pts.reset();
-    }
 
     int thirdFromLastPt = 0, nextPt = 0;
 
@@ -572,14 +547,17 @@ public:
       // a joinStroke pass with a retained "Last" trace policy
       // (i.e. the user confirms draw a line while he is holding
       // the SHIFT key))
-      if (c == 0 && m_retainedTracePolicyLast)
+      if (c == 0 && loop->getTracePolicy() == TracePolicy::Last)
         continue;
 
       // For the last point we need to store the source image content at that
       // point so we can restore it when erasing a point because of
       // pixel-perfect. So we set the following flag to indicate this, and
       // use it in doTransformPoint.
-      m_saveStrokeArea = (c == m_pts.size() - 1);
+      // The previous behavior isn't required for LineFreehand controller and
+      // the trace policy is "Last" (i.e. the user is drawing a line while
+      // he is holding the SHIFT key)
+      m_saveStrokeArea = ((c == m_pts.size() - 1) && loop->getTracePolicy() != TracePolicy::Last);
       if (m_saveStrokeArea) {
         clearPointshapeStrokePtAreas();
         setLastPtIndex(c);