Improve subclassing cababilities of Fl_Tile (STR 2791)

- remove static variables and functions
- make move_intersection() virtual
- add (protected) cursor access methods

These changes were inspired by STR 2791 where the user proposing an
enhancement was not able to subclass Fl_Tile properly. This commit
fixes the mentioned issues and enables subclassing without copying
internal code.

3 files changed, 67 insertions, 36 deletions

diff --git a/FL/Fl_Tile.H b/FL/Fl_Tile.H
index af104a4eb..a7de02fea 100644
--- a/FL/Fl_Tile.H
+++ b/FL/Fl_Tile.H
@@ -1,7 +1,7 @@
 //
 // Tile header file for the Fast Light Tool Kit (FLTK).
 //
-// Copyright 1998-2016 by Bill Spitzak and others.
+// Copyright 1998-2023 by Bill Spitzak and others.
 //
 // This library is free software. Distribution and use rights are outlined in
 // the file "COPYING" which should have been included with this file. If this
@@ -29,10 +29,24 @@ public:
   int handle(int event) FL_OVERRIDE;
   Fl_Tile(int X, int Y, int W, int H, const char *L=0);
   void resize(int X, int Y, int W, int H) FL_OVERRIDE;
-  void move_intersection(int oldx, int oldy, int newx, int newy);
+  virtual void move_intersection(int oldx, int oldy, int newx, int newy);
   FL_DEPRECATED("in 1.4.0 - use move_intersection(p) instead",
-  void position(int oldx, int oldy, int newx, int newy)) { return move_intersection(oldx, oldy, newx, newy); }
+  void position(int oldx, int oldy, int newx, int newy)) { move_intersection(oldx, oldy, newx, newy); }
   void position(int x, int y) { Fl_Group::position(x, y); }
+
+protected:
+  int cursor_;                  ///< current cursor index (0..3)
+  Fl_Cursor *cursors_;          ///< points at the array of 4 cursors (may be overridden)
+
+  /** Returns the cursor for cursor index n.
+    \see Fl_Tile::set_cursor(int)
+  */
+
+  Fl_Cursor cursor(int n) {
+    return cursors_[n];
+  }
+
+  void set_cursor(int n);       // set one of n (0..3) cursors
 };
 
 #endif
diff --git a/src/Fl_Tile.cxx b/src/Fl_Tile.cxx
index a5de6039d..5c238e487 100644
--- a/src/Fl_Tile.cxx
+++ b/src/Fl_Tile.cxx
@@ -87,6 +87,13 @@
 #include <FL/Fl_Rect.H>
 #include <stdlib.h>
 
+static Fl_Cursor Fl_Tile_cursors[4] = {
+  FL_CURSOR_DEFAULT,  // 0 normal
+  FL_CURSOR_WE,       // 1 drag horizontally
+  FL_CURSOR_NS,       // 2 drag vertically
+  FL_CURSOR_MOVE      // 3 move intersection
+};
+
 /**
   Drags the intersection at (\p oldx,\p oldy) to (\p newx,\p newy).
   This redraws all the necessary children.
@@ -173,30 +180,33 @@ void Fl_Tile::resize(int X,int Y,int W,int H) {
   }
 }
 
-static void set_cursor(Fl_Tile*t, Fl_Cursor c) {
-  static Fl_Cursor cursor;
-  if (cursor == c || !t->window()) return;
-  cursor = c;
-#ifdef __sgi
-  t->window()->cursor(c,FL_RED,FL_WHITE);
-#else
-  t->window()->cursor(c);
-#endif
+/**
+  Set one of four cursors used for dragging etc..
+
+  Fl_Tile uses an array of four cursors that are set depending on user actions:
+    - 0: normal cursor
+    - 1: horizontal dragging
+    - 2: vertical dragging
+    - 3: dragging an intersection
+
+  This method sets the window cursor for the given index \p n.
+*/
+void Fl_Tile::set_cursor(int n) {
+  if (n < 0 || n > 3) n = 0;      // check array index
+  cursor_ = n;                    // always store the index
+  if (cursor_ == n || !window())
+    return;
+  window()->cursor(cursor(n));
 }
 
-static Fl_Cursor cursors[4] = {
-  FL_CURSOR_DEFAULT,
-  FL_CURSOR_WE,
-  FL_CURSOR_NS,
-  FL_CURSOR_MOVE};
+#define DRAGH 1
+#define DRAGV 2
+#define GRABAREA 4
 
 int Fl_Tile::handle(int event) {
   static int sdrag;
   static int sdx, sdy;
   static int sx, sy;
-#define DRAGH 1
-#define DRAGV 2
-#define GRABAREA 4
 
   int mx = Fl::event_x();
   int my = Fl::event_y();
@@ -239,13 +249,13 @@ int Fl_Tile::handle(int event) {
     sdrag = 0; sx = sy = 0;
     if (mindx <= GRABAREA) {sdrag = DRAGH; sx = oldx;}
     if (mindy <= GRABAREA) {sdrag |= DRAGV; sy = oldy;}
-    set_cursor(this, cursors[sdrag]);
+    set_cursor(sdrag);
     if (sdrag) return 1;
     return Fl_Group::handle(event);
   }
 
   case FL_LEAVE:
-    set_cursor(this, FL_CURSOR_DEFAULT);
+    set_cursor(0); // set default cursor
     break;
 
   case FL_DRAG:
@@ -264,10 +274,13 @@ int Fl_Tile::handle(int event) {
     int newy;
     if (sdrag&DRAGV) {
       newy = Fl::event_y()-sdy;
-      if (newy < r->y()) newy = r->y();
-      else if (newy > r->y()+r->h()) newy = r->y()+r->h();
-    } else
+      if (newy < r->y())
+        newy = r->y();
+      else if (newy > r->y()+r->h())
+        newy = r->y()+r->h();
+    } else {
       newy = sy;
+    }
     move_intersection(sx, sy, newx, newy);
     if (event == FL_DRAG) {
       set_changed();
@@ -275,9 +288,10 @@ int Fl_Tile::handle(int event) {
     } else {
       do_callback(FL_REASON_CHANGED);
     }
-    return 1;}
+    return 1;
+    } // case FL_RELEASE
 
-  }
+  } // switch()
 
   return Fl_Group::handle(event);
 }
@@ -297,6 +311,8 @@ int Fl_Tile::handle(int event) {
 */
 
 Fl_Tile::Fl_Tile(int X,int Y,int W,int H,const char*L)
-: Fl_Group(X,Y,W,H,L)
+: Fl_Group(X,Y,W,H,L),
+  cursor_(0),
+  cursors_(Fl_Tile_cursors)
 {
 }
diff --git a/test/tile.cxx b/test/tile.cxx
index 2b6485ef2..e8b1d6318 100644
--- a/test/tile.cxx
+++ b/test/tile.cxx
@@ -1,7 +1,7 @@
 //
 // Fl_Tile test program for the Fast Light Tool Kit (FLTK).
 //
-// Copyright 1998-2016 by Bill Spitzak and others.
+// Copyright 1998-2023 by Bill Spitzak and others.
 //
 // This library is free software. Distribution and use rights are outlined in
 // the file "COPYING" which should have been included with this file.  If this
@@ -19,18 +19,19 @@
 #include <FL/Fl_Tile.H>
 #include <FL/Fl_Box.H>
 
-//#define TEST_INACTIVE
+// #define TEST_INACTIVE
 
 int main(int argc, char** argv) {
-  Fl_Double_Window window(300,300);
+  Fl_Double_Window window(300, 300);
   window.box(FL_NO_BOX);
   window.resizable(window);
 
-  int dx = 20, dy = dx; // border width of resizable() - see below
-  Fl_Tile tile(0,0,300,300);
+  Fl_Tile tile(0, 0, 300, 300);
 
   // create the symmetrical resize box with dx and dy pixels distance, resp.
   // from the borders of the Fl_Tile widget before all other children
+
+  int dx = 20, dy = dx; // border width of resizable()
   Fl_Box r(tile.x()+dx,tile.y()+dy,tile.w()-2*dx,tile.h()-2*dy);
   tile.resizable(r);
 
@@ -62,9 +63,9 @@ int main(int argc, char** argv) {
   box2b.color(13);
   box2b.labelsize(36);
   box2b.align(FL_ALIGN_CLIP);
-  //tile2.end();
+  // tile2.end();
 
-  //Fl_Tile tile3(150,150,150,150);
+  // Fl_Tile tile3(150,150,150,150);
   Fl_Box box3a(150,150,150,70,"3a");
   box3a.box(FL_DOWN_BOX);
   box3a.color(12);
@@ -76,7 +77,7 @@ int main(int argc, char** argv) {
   box3b.color(13);
   box3b.labelsize(36);
   box3b.align(FL_ALIGN_CLIP);
-  //tile3.end();
+  // tile3.end();
 
   tile.end();
   window.end();