Fix straight line while drawing on pixel perfect

src/app/tools/intertwiners.h

@@ -384,6 +384,11 @@ 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 retainedTracePolicyLast = false;
   Stroke m_pts;
 
 public:
@@ -393,6 +398,7 @@ public:
 
   void prepareIntertwine() override {
     m_pts.reset();
+    retainedTracePolicyLast = false;
   }
 
   void joinStroke(ToolLoop* loop, const Stroke& stroke) override {
@@ -401,8 +407,10 @@ 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)
+    if (loop->getTracePolicy() == TracePolicy::Last) {
+      retainedTracePolicyLast = true;
       m_pts.reset();
+    }
 
     if (stroke.size() == 0)
       return;
@@ -435,6 +443,12 @@ public:
         ++c;
       }
 
+      // We must ignore to print the first point of the line after
+      // 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 && retainedTracePolicyLast)
+        continue;
       doPointshapePoint(m_pts[c].x, m_pts[c].y, loop);
     }
   }

src/app/tools/tool_loop_manager.cpp

@@ -77,6 +77,16 @@ void ToolLoopManager::pressButton(const Pointer& pointer)
 {
   TOOL_TRACE("ToolLoopManager::pressButton", pointer.point());
 
+  // A little patch to memorize initial Trace Policy in the
+  // current function execution.
+  // When the initial trace policy is "Last" and then
+  // changes to different trace policy at the end of
+  // this function, the user confirms a line draw while he
+  // is holding the SHIFT key.
+  bool tracePolicyWasLast = false;
+  if (m_toolLoop->getTracePolicy() == TracePolicy::Last)
+    tracePolicyWasLast = true;
+
   m_lastPointer = pointer;
 
   if (isCanceled())
@@ -102,7 +112,18 @@ void ToolLoopManager::pressButton(const Pointer& pointer)
   m_toolLoop->getController()->getStatusBarText(m_toolLoop, m_stroke, statusText);
   m_toolLoop->updateStatusBar(statusText.c_str());
 
-  doLoopStep(false);
+  // We evaluate if the trace policy has changed compared with
+  // the initial trace policy.
+  if (!(m_toolLoop->getTracePolicy() == TracePolicy::Last) &&
+        tracePolicyWasLast) {
+    // Do nothing. We do not need execute an additional doLoopStep
+    // (which it want to accumulate more points in m_pts in function
+    // joinStroke() from intertwiners.h)
+    // This avoid double print of a line while the user holds down
+    // the SHIFT key.
+  }
+  else
+    doLoopStep(false);
 }
 
 bool ToolLoopManager::releaseButton(const Pointer& pointer)