Refactor and simplify "arrow drawing" in widgets

"Arrows" in widgets are those GUI elements mostly represented by
triangles pointing in a particular direction as in scrollbars,
choice widgets, some menus, valuators and Fl_Counter widgets.

The code has been simplified and standardized such that all these
GUI elements are drawn identically per FLTK scheme.

Widget authors no longer need to write code to calculate arrow sizes
and draw polygons etc.

Different schemes can and do implement different drawing functions.

Todo: see comments "FIXME_ARROW" in src/Fl_Menu_Button.cxx and
      src/Fl_Menu.cxx

1 files changed, 51 insertions, 42 deletions

diff --git a/src/Fl_Choice.cxx b/src/Fl_Choice.cxx
index 20b374442..c23010c07 100644
--- a/src/Fl_Choice.cxx
+++ b/src/Fl_Choice.cxx
@@ -1,7 +1,7 @@
 //
 // Choice widget for the Fast Light Tool Kit (FLTK).
 //
-// Copyright 1998-2015 by Bill Spitzak and others.
+// Copyright 1998-2022 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
@@ -22,6 +22,11 @@
 // Emulates the Forms choice widget.  This is almost exactly the same
 // as an Fl_Menu_Button.  The only difference is the appearance of the
 // button: it draws the text of the current pick and a down-arrow.
+// The exact layout and the type of arrow can vary by FLTK scheme.
+
+// FIXME: all such variations should be implemented in the "scheme code",
+// hopefully in a future class derived from a base class Fl_Scheme or similar.
+// Albrecht
 
 void Fl_Choice::draw() {
   Fl_Boxtype btype = Fl::scheme() ? FL_UP_BOX           // non-default uses up box
@@ -32,70 +37,74 @@ void Fl_Choice::draw() {
   // Arrow area
   int H = h() - 2 * dy;
   int W = Fl::is_scheme("gtk+")    ? 20 :                       // gtk+  -- fixed size
-          Fl::is_scheme("gleam")   ? 20 :                       // gleam -- fixed size
-          Fl::is_scheme("plastic") ? ((H > 20) ? 20 : H)        // plastic: shrink if H<20
-                                   : ((H > 20) ? 20 : H);       // default: shrink if H<20
+          Fl::is_scheme("gleam")   ? 20                         // gleam -- fixed size
+                                   : ((H > 20) ? 20 : H);       // else: shrink if H<20
   int X = x() + w() - W - dx;
   int Y = y() + dy;
 
-  // Arrow object
-  int w1 = (W - 4) / 3; if (w1 < 1) w1 = 1;
-  int x1 = X + (W - 2 * w1 - 1) / 2;
-  int y1 = Y + (H - w1 - 1) / 2;
+  Fl_Rect ab(X, Y, W, H); // arrow box
+  int active = active_r();
+  Fl_Color arrow_color = active ? labelcolor() : fl_inactive(labelcolor());
+  Fl_Color box_color = color();
+
+  // From "original" code: modify the box color *only* for the default scheme.
+  // This is weird (why?). I believe we should either make sure that the text
+  // color contrasts well when the text is rendered *or* we should do this for
+  // *all* schemes. Anyway, adapting the old code... (Albrecht)
+
+  if (!Fl::scheme()) {            // default scheme only, see comment above
+    if (fl_contrast(textcolor(), FL_BACKGROUND2_COLOR) == textcolor())
+      box_color = FL_BACKGROUND2_COLOR;
+    else
+      box_color = fl_lighter(color());
+  }
 
-  if (Fl::scheme()) {
-    // NON-DEFAULT SCHEME
+  // Draw the widget box
 
-    // Draw widget box
-    draw_box(btype, color());
+  draw_box(btype, box_color);
 
-    // Draw arrow area
-    fl_color(active_r() ? labelcolor() : fl_inactive(labelcolor()));
-    if (Fl::is_scheme("plastic")) {
-      // Show larger up/down arrows...
-      fl_polygon(x1, y1 + 3, x1 + w1, y1 + w1 + 3, x1 + 2 * w1, y1 + 3);
-      fl_polygon(x1, y1 + 1, x1 + w1, y1 - w1 + 1, x1 + 2 * w1, y1 + 1);
-    } else {
-      // Show smaller up/down arrows with a divider...
-      x1 = x() + w() - 13 - dx;
-      y1 = y() + h() / 2;
-      fl_polygon(x1, y1 - 2, x1 + 3, y1 - 5, x1 + 6, y1 - 2);
-      fl_polygon(x1, y1 + 2, x1 + 3, y1 + 5, x1 + 6, y1 + 2);
+  // Arrow box or horizontal divider line, depending on the current scheme
+
+  // Scheme:          Box or divider line
+  // ----------------------------------------
+  // Default (None):  Arrow box (FL_UP_BOX)
+  // gtk+, gleam:     Divider line
+  // else:            Nothing (!)
+
+  if (Fl::scheme()) {
+    if (Fl::is_scheme("gtk+") ||
+        Fl::is_scheme("gleam")) {
+      // draw the divider
+      int x1 = x() + w() - 20 - dx;
+      int y1 = y() + h() / 2;
 
       fl_color(fl_darker(color()));
-      fl_yxline(x1 - 7, y1 - 8, y1 + 8);
+      fl_yxline(x1, y1 - 8, y1 + 8);
 
       fl_color(fl_lighter(color()));
-      fl_yxline(x1 - 6, y1 - 8, y1 + 8);
-    }
-  } else {
-    // DEFAULT SCHEME
-
-    // Draw widget box
-    if (fl_contrast(textcolor(), FL_BACKGROUND2_COLOR) == textcolor()) {
-      draw_box(btype, FL_BACKGROUND2_COLOR);
-    } else {
-      draw_box(btype, fl_lighter(color()));
+      fl_yxline(x1 + 1, y1 - 8, y1 + 8);
     }
-
-    // Draw arrow area
-    draw_box(FL_UP_BOX,X,Y,W,H,color());
-    fl_color(active_r() ? labelcolor() : fl_inactive(labelcolor()));
-    fl_polygon(x1, y1, x1 + w1, y1 + w1, x1 + 2 * w1, y1);
+  } else { // Default scheme ("None")
+    // Draw arrow box
+    draw_box(FL_UP_BOX, X, Y, W, H, color());
+    ab.inset(FL_UP_BOX);
   }
 
+  // Draw choice arrow(s)
+  fl_draw_arrow(ab, FL_ARROW_CHOICE, FL_ORIENT_NONE, arrow_color);
+
   W += 2 * dx;
 
   // Draw menu item's label
   if (mvalue()) {
     Fl_Menu_Item m = *mvalue();
-    if (active_r()) m.activate(); else m.deactivate();
+    if (active) m.activate(); else m.deactivate();
 
     // Clip
     int xx = x() + dx, yy = y() + dy + 1, ww = w() - W, hh = H - 2;
     fl_push_clip(xx, yy, ww, hh);
 
-    if ( Fl::scheme()) {
+    if (Fl::scheme()) {
       Fl_Label l;
       l.value = m.text;
       l.image = 0;