Optimize "arrow" drawing and centering

- center (sub)menu arrow as good as possible
- adjust arrow sizes in Fl_Counter widget
- refactor "oxy" arrow drawing and centering in widgets

src/Fl_Counter.cxx

@@ -62,7 +62,7 @@ void Fl_Counter::arrow_widths(int &w1, int &w2) {
     w2 = w() * 17/100;
   }
   // limit arrow box sizes to reserve more space for the text box
-  if (w1 > 18) w1 = 18;
+  if (w1 > 13) w1 = 13;
   if (w2 > 24) w2 = 24;
 }
 

src/Fl_Menu.cxx

@@ -526,10 +526,10 @@ void menuwindow::drawentry(const Fl_Menu_Item* m, int n, int eraseit) {
   if (m->submenu()) {
 
     // calculate the bounding box of the submenu pointer (arrow)
-    int sz = (hh-2) & -2;
+    int sz = ((hh-2) & (-2)) + 1 ;  // must be odd for better centering
-    if (sz > 12) sz = 12; // limit arrow size => max(d) = (sz-2)/2 = 5
+    if (sz > 13) sz = 13;           // limit arrow size
-    int x1 = xx + ww - sz - 2;
+    int x1 = xx + ww - sz - 2;      // left border
-    int y1 = yy + (hh-sz)/2 + 1;
+    int y1 = yy + (hh-sz)/2 + 1;    // top border
 
     // draw an arrow whose style depends on the active scheme
     fl_draw_arrow(Fl_Rect(x1, y1, sz, sz), FL_ARROW_SINGLE, FL_ORIENT_RIGHT, fl_color());

src/fl_oxy.cxx

@@ -2,7 +2,7 @@
 // "Oxy" Scheme drawing routines for the Fast Light Tool Kit (FLTK).
 //
 // Copyright 2011 by Dmitrij K. aka "kdiman"
-// Copyright 2012-2022 by Bill Spitzak and others.
+// Copyright 2012-2024 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
@@ -20,66 +20,74 @@
 #include <FL/Fl_Rect.H>
 #include "fl_oxy.h"
 
-// Status of this scheme (to-do list):
+// Note:
 //
-// This scheme works but is not yet perfect:
+// Drawing on the X11 platform w/o Cairo can be asymmetric for some "arrows"
-//
-// (1) Drawing on the X11 platform (w/o Cairo) can be asymmetric for some "arrows"
-// (2) Arrows are not always centered perfectly
 
 #define GROFF 0.45f // gradients offset
 
-// Draw a single arrow
+#ifndef DEBUG_OXY_ARROW
-static void single_arrow(Fl_Rect bb, Fl_Orientation o, Fl_Color col) {
+#define DEBUG_OXY_ARROW 0   // 0 = off, 1 = cross at center position of arrows
+#endif
 
-  fl_color(col);
+// Draw a single arrow
-  fl_line_style(FL_SOLID, 1);
+
-  fl_push_matrix();
+static void single_arrow(Fl_Rect bb, Fl_Orientation o, Fl_Color col) {
 
   int x1 = bb.x();
   int y1 = bb.y();
   int w1 = bb.w();
   int h1 = bb.h();
 
-  int dx = w1 / 3;
-  if (h1 < w1) dx = h1 / 3;
-  if (dx > 4) dx = 4;
-  else if (dx < 2) dx = 2;
-
   float angle = int(o) * 45.0f;
 
-  int tx = x1 + (w1 + 1)/2;
+  // calculate arrow size
-  int ty = y1 + (h1 + 1)/2;
+  int dx = (w1 - 3) / 2;
+  if (h1 < w1) dx = (h1 - 3) / 2;
+  if (dx > 4) dx = 4;
+  else if (dx < 2) dx = 2;
+  // dx = (dx + 1) & (-2);  // should be even ? not required
 
-  const int lw = 2;       // arrow line width: n means n+1 pixels
+  int tx = x1 + w1/2;
+  int ty = y1 + h1/2;
 
-  // define translation adjustments for easier maintenance
+  const int lw = 2;         // arrow line width: n+1 pixels (must be even)
+  const int dw = 1;         // half the line width
 
-  static int tr_x =  0;
+  fl_color(col);
-  static int tr_y = -1;
+  fl_line_style(FL_SOLID, 1);
+  fl_push_matrix();
 
-  if (o == FL_ORIENT_LEFT)
+  fl_translate(tx, ty);     // move to center
-    tr_x = 2;
+  fl_rotate(angle);         // rotate by given angle
 
-  if (o & 2)              // up or down arrow
+  // DEBUG: Draw a two-colored cross at the center of the arrow box
-    fl_translate(tx, ty - (lw+1)/2 + tr_y);
+  // This can be used to debug or adjust array alignment (centering)
-  else                    // left or right arrow
-    fl_translate(tx - lw/2 + tr_x, ty);
 
-  fl_rotate(angle);
+#if (DEBUG_OXY_ARROW)                   // draw a cross at the center
+  int ll;                               // line length
+  fl_color(FL_BLUE);                    // "horizontal" line
+  ll = (o&2) ? h1/2 - 1 : w1/2 - 1;     // line length
+  fl_begin_line();
+  fl_vertex(-ll, 0); fl_vertex(ll, 0);
+  fl_end_line();
+  fl_color(0x22882200);                 // "vertical" line
+  ll = (o&2) ? w1/2 - 1 : h1/2 - 1;     // line length
+  fl_begin_line();
+  fl_vertex(0, -ll); fl_vertex(0, ll);
+  fl_end_line();
+  fl_color(col);                        // back to original color
+#endif
 
-  int x0 = (-dx)/2;
+  // Draw the "arrow", similar to '>' at the center of the box
 
   fl_begin_complex_polygon();
-
+  fl_vertex(-dx + dw,      -dx);
-  fl_vertex(x0,          -dx);
+  fl_vertex(  0 + dw,        0);
-  fl_vertex(x0 + dx,      0);
+  fl_vertex(-dx + dw,       dx);
-  fl_vertex(x0,           dx);
+  fl_vertex(-dx + dw + lw,  dx);
-
+  fl_vertex(  0 + dw + lw,   0);
-  fl_vertex(x0 + lw,      dx);
+  fl_vertex(-dx + dw + lw, -dx);
-  fl_vertex(x0 + lw + dx, 0);
-  fl_vertex(x0 + lw,     -dx);
-
   fl_end_complex_polygon();
 
   fl_pop_matrix();
@@ -105,14 +113,12 @@ void oxy_arrow(Fl_Rect bb, Fl_Arrow_Type t, Fl_Orientation o, Fl_Color col) {
       switch (int(o)) {
         case FL_ORIENT_DOWN:
         case FL_ORIENT_UP:
-          bb.y(bb.y() - 2);           // shift upwards
           bb.h(bb.h() - 4);           // reduce size
           single_arrow(bb, o, col);
           bb.y(bb.y() + 4);           // shift down
           single_arrow(bb, o, col);
           break;
         default:
-          bb.x(bb.x() - 1);           // shift left
           bb.w(bb.w() - 4);           // reduce size
           single_arrow(bb, o, col);
           bb.x(bb.x() + 4);           // shift right
@@ -123,10 +129,10 @@ void oxy_arrow(Fl_Rect bb, Fl_Arrow_Type t, Fl_Orientation o, Fl_Color col) {
 
     case FL_ARROW_CHOICE:
 
-      // bb.y(bb.y() - 0);            // don't shift upwards (was: -2)
+      bb.y(bb.y() - 1);               // shift upwards
-      bb.h(bb.h() - 4);               // reduce size
+      bb.h(bb.h() - 4);               // reduce height
       single_arrow(bb, FL_ORIENT_UP, col);
-      bb.y(bb.y() + 4);               // shift down
+      bb.y(bb.y() + 6);               // shift down
       single_arrow(bb, FL_ORIENT_DOWN, col);
       break;