1 files changed, 73 insertions, 0 deletions
diff --git a/fluid/widgets/Formula_Input.h b/fluid/widgets/Formula_Input.h
new file mode 100644
index 000000000..5307cdc88
--- /dev/null
+++ b/fluid/widgets/Formula_Input.h
@@ -0,0 +1,73 @@
+//
+// Formula_Input widget header file for the Fast Light Tool Kit (FLTK).
+//
+// Copyright 1998-2025 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
+// file is missing or damaged, see the license at:
+//
+//     https://www.fltk.org/COPYING.php
+//
+// Please see the following page on how to report bugs and issues:
+//
+//     https://www.fltk.org/bugs.php
+//
+
+#ifndef FLUID_WIDGETS_FORMULA_INPUT_H
+#define FLUID_WIDGETS_FORMULA_INPUT_H
+
+#include <FL/Fl_Input.H>
+
+namespace fld {
+namespace widget {
+
+class Formula_Input;
+
+// Callback signature for function returning the value of a variable.
+typedef int (Fluid_Coord_Callback)(Formula_Input const *, void*);
+
+// Entry for a list of variables available to an input field.
+// Formula_Input::variables() expects an array of
+// Formula_Input_Vars with the last entry's name_ set to NULL.
+typedef struct Formula_Input_Vars {
+  const char *name_;
+  Fluid_Coord_Callback *callback_;
+} Formula_Input_Vars;
+
+// A text input widget that understands simple math.
+class Formula_Input : public Fl_Input
+{
+  Fl_Callback *user_callback_ { nullptr };
+  Formula_Input_Vars *vars_ { nullptr };
+  void *vars_user_data_ { nullptr };
+
+  static void callback_handler_cb(Formula_Input *This, void *v);
+  void callback_handler(void *v);
+  int eval_var(uchar *&s) const;
+  int eval(uchar *&s, int prio) const;
+  int eval(const char *s) const;
+  
+public:
+  Formula_Input(int x, int y, int w, int h, const char *l = nullptr);
+
+  /** Return the text in the widget text field. */
+  const char *text() const { return Fl_Input::value(); }
+  
+  /** Set the text in the text field */
+  void text(const char *v) { Fl_Input::value(v); }
+  
+  int value() const;
+  void value(int v);
+  
+  /** Set the general callback for this widget. */
+  void callback(Fl_Callback *cb) { user_callback_ = cb; }
+
+  void variables(fld::widget::Formula_Input_Vars *vars, void *user_data);
+  int handle(int) override;
+};
+
+} // namespace widget
+} // namespace fld
+
+#endif // FLUID_WIDGETS_FORMULA_INPUT_H