fltk/FL/Fl_Cairo_Window.H

//
// Fl_Cairo_Window header file for the Fast Light Tool Kit (FLTK).
//
// 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
// 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
//

/** \file FL/Fl_Cairo_Window.H
  \brief Fl_Cairo_Window, an FLTK window incorporating a Cairo draw callback.
*/

#ifndef FL_CAIRO_WINDOW_H
# define FL_CAIRO_WINDOW_H

#include <FL/fl_config.h>

# ifdef FLTK_HAVE_CAIRO

// Cairo is currently supported for the following platforms:
// Win32, Apple Quartz, X11, Wayland

#  include <FL/Fl.H>
#  include <FL/Fl_Double_Window.H>

/**
   \addtogroup group_cairo
   @{
*/

/**
  This defines an FLTK window with Cairo support.

  This class overloads the virtual draw() method for you,
  so that the only thing you have to do is to provide your Cairo code.
  All Cairo context handling is achieved transparently.

  The default coordinate system for Cairo drawing commands within Fl_Cairo_Window
  is FLTK's coordinate system, where the `x,y,w,h` values are relative to the
  top/left corner of the Fl_Cairo_Window, as one would expect with regular
  FLTK drawing commands, e.g.: `(0 ≤ x ≤ w-1), (0 ≤ y ≤ h-1)`.
  \b Example:
  \code
  static void my_cairo_draw_cb(Fl_Cairo_Window *window, cairo_t *cr) {
    // Draw an "X"
    const double xmax = (window->w() - 1);
    const double ymax = (window->h() - 1);
    cairo_set_line_width(cr, 1.00);                               // line width for drawing
    cairo_set_source_rgb(cr, 1.0, 0.5, 0.0);                      // orange
    cairo_move_to(cr, 0.0, 0.0);  cairo_line_to(cr, xmax, ymax);  // draw diagonal "\"
    cairo_move_to(cr, 0.0, ymax); cairo_line_to(cr, xmax, 0.0);   // draw diagonal "/"
    cairo_stroke(cr);                                             // stroke the lines
  }
  \endcode

  The FLTK coordinate system differs from the default native Cairo coordinate system
  which uses normalized `(0.0 … 1.0)` values for x and y, e.g.: `(0 ≤ x ≤ 1.0), (0 ≤ y ≤ 1.0)`.
  So beware of this when copy/pasting Cairo example programs that assume normalized values.
  If need be, you can revert to the Cairo coordinate system by simply calling `cairo_scale()`
  with the widget's `w()` and `h()` values. \b Example:

  \code
  static void my_cairo_draw_cb(Fl_Cairo_Window *window, cairo_t *cr) {
    cairo_scale(cr, window->w(), window->h());    // use Cairo's default coordinate system
    [..use 0.0 to 1.0 values from here on..]
  }
  \endcode

  \see examples/cairo-draw-x.cxx
  \see test/cairo_test.cxx

  \note Class Fl_Cairo_Window requires the FLTK library to have been built with
  CMake option FLTK_OPTION_CAIRO_WINDOW or configure --enable-cairo.

  \note You can alternatively define your custom Cairo FLTK window,
  and thus at least override the draw() method to provide custom Cairo
  support. In this case you will probably use Fl::cairo_make_current(Fl_Window*)
  to attach a context to your window. You should do this only when your window is
  the current window. \see Fl_Window::current()
*/
class FL_EXPORT Fl_Cairo_Window : public Fl_Double_Window {

public:
  Fl_Cairo_Window(int W, int H, const char *L = 0)
    : Fl_Double_Window(W, H, L), draw_cb_(0) {}
  Fl_Cairo_Window(int X, int Y, int W, int H, const char *L = 0)
    : Fl_Double_Window(X, Y, W, H, L), draw_cb_(0) {}

protected:
  /** Overloaded to provide Cairo callback support. */
  void draw() FL_OVERRIDE {
    Fl_Double_Window::draw();
    if (draw_cb_) { // call the Cairo draw callback
      // manual method ? if yes explicitly get a cairo_context here
      if (!Fl::cairo_autolink_context())
        Fl::cairo_make_current(this);
      draw_cb_(this, Fl::cairo_cc());
      // flush Cairo drawings: necessary at least for Windows
      Fl::cairo_flush(Fl::cairo_cc());
    }
  }

public:
  /** The Cairo draw callback prototype you need to implement. */
  typedef void (*cairo_draw_cb) (Fl_Cairo_Window* self, cairo_t* def);

  /**
    You must provide a draw callback that implements your Cairo rendering.
    This method permits you to set your Cairo callback to \p cb.
  */
  void set_draw_cb(cairo_draw_cb cb) { draw_cb_ = cb; }
private:
    cairo_draw_cb draw_cb_;
};


/** @} */

# endif // FLTK_HAVE_CAIRO
#endif // FL_CAIRO_WINDOW_H