lumiera_/research/gtk-style-experiment.cpp

/*
  gtk-style-experiment.cpp  -  simple application to investigate GTK styling

   Copyright (C)
     2019,            Hermann Vosseler <Ichthyostega@web.de>

  **Lumiera** is free software; you can redistribute it and/or modify it
  under the terms of the GNU General Public License as published by the
  Free Software Foundation; either version 2 of the License, or (at your
  option) any later version. See the file COPYING for further details.
*/


/** @file gtk-style-experiment.cpp
 ** Simple GTK Application frame to investigate some aspects of GTK's CSS implementation.
 ** Especially the goal is to _grab some existing CSS styling_ with a Gtk::StyleContext
 ** and use this for custom drawing. Within Lumiera, we use custom drawing for some parts
 ** of the Timeline UI presentation.
 ** 
 ** # Setup for investigation
 ** - add a separate dummy Gtk::Frame widget as `testFrame_`
 ** - apply custom styling to that frame, by virtue of a CSS class '.experiment'
 ** - pick up the Gtk::StyleContext of that `testFrame_` to get the CSS path
 ** - build a "free standing" new Gtk::StyleContext and apply the CSS path found
 ** - use this style context to draw a custom frame and background onto the canvas
 ** - control extension of that custom drawing through the top margin CSS setting of testFrame_
 ** 
 ** # Findings
 ** - it works as intended
 ** - however, care must be taken to apply CSS cascading properly (generic vs specific selectors)
 ** - the context_save/restore functionality seems to be broken on a "free standing" style context;
 **   however it works as expected on a style context associated to an existing and realised widget.
 ** - workaround is to add / remove classes explicitly.
 ** - CSS3 effects like box-shadow are applied with the StyleContext::render_background() function
 **   * first, an outset box-shadow is rendered _outside_ the box given as parameter to `render_background()`
 **   * then the box is filled with the background colour
 **   * and last, an inset box-shadow is rendered _inside_ the area of a would-be border,
 **     without rendering the border itself.
 **   * consequently we can not shade the border itself and we can not shade the content
 ** 
 ** @see stage::timeline::BodyCanvasWidget
 */


#include "stage/gtk-base.hpp"
#include "lib/searchpath.hpp"
#include "lib/format-cout.hpp"
#include "lib/format-util.hpp"
#include "lib/error.hpp"
#include "lib/util.hpp"

#include <string>

using util::join;
using std::string;

namespace research {
  
  namespace {
    const string STYLESHEET_NAME{"gtk-style-experiment.css"};
    const string RESOURCE_PATH  {"$ORIGIN/gui"};
    
    const string CLASS_experiment{"experiment"};
    const string CLASS_slopeDeep1{"track-slope-deep1"};
    
    string
    slopeClassName(int depth)
    {
      switch (depth)
        {
          case 1: return "track-slope-deep1";
          case 2: return "track-slope-deep2";
          case 3: return "track-slope-deep3";
          case 4: return "track-slope-deep4";
          default:return "track-slope-verydeep";
        }
    }
  }
  
  using CairoC = stage::PCairoContext const&;
  using StyleC = stage::PStyleContext const&;
  
  using stage::PStyleContext;
  
  
  class Canvas
    : public Gtk::Layout
    {
      bool shallDraw_       = false;
      bool recalcExtension_ = false;
      
      StyleC style_;
      
    public:
      Canvas(StyleC refStyle)
        : style_{refStyle}
      { }
      
      void adjustSize();
      void enableDraw (bool);
      
      int xBorderSiz = 1;
      int xObservedSize = -1;
      string xObservedPath;
      string xObservedClzz;
      
    private:
      virtual bool on_draw (Cairo::RefPtr<Cairo::Context> const&)  override;
      
      void determineExtension();
    };


  class StyleTestPanel
    : public Gtk::Box
    {
    public:
      StyleTestPanel();
      
    private:
      Gtk::Box twoParts_;
      Gtk::ButtonBox buttons_;
      Gtk::Button button_1_;
      Gtk::Button button_2_;
      Gtk::CheckButton toggleDraw_;
      Gtk::Frame testFrame_;
      Gtk::Frame frame_;
      Gtk::ScrolledWindow scroller_;
      
      PStyleContext pStyle_;
      Canvas canvas_;
      
      PStyleContext setupStyle(Gtk::Widget const&);
      
      void experiment_1();
      void experiment_2();
    };
  
  
  /* ===== Implementation ===== */
  
  StyleTestPanel::StyleTestPanel()
    : Box{}
    , twoParts_{Gtk::ORIENTATION_VERTICAL}
    , buttons_{}
    , testFrame_{"testFrame"}
    , frame_{"Gtk::StyleContext Experiments"}
    , scroller_{}
    , pStyle_{}
    , canvas_{pStyle_}
    {
      twoParts_.pack_start(buttons_, Gtk::PACK_SHRINK);
      twoParts_.pack_start(frame_);
      
      buttons_.set_layout(Gtk::BUTTONBOX_START);
      
      // buttons to trigger experiments
      button_1_.set_label("_grow");
      button_1_.set_use_underline();
      button_1_.set_tooltip_markup("<b>Experiment 1</b>:\ngrow the border size");
      button_1_.signal_clicked().connect(
                  mem_fun(*this, &StyleTestPanel::experiment_1));
      buttons_.add(button_1_);
      
      button_2_.set_label("_dump");
      button_2_.set_use_underline();
      button_2_.set_tooltip_markup("<b>Experiment 2</b>:\ndump style information");
      button_2_.signal_clicked().connect(
                  mem_fun(*this, &StyleTestPanel::experiment_2));
      buttons_.add(button_2_);
      
      // a Gtk::Frame widget used as source for our StyleContext
      testFrame_.get_style_context()->add_class(CLASS_experiment);
      testFrame_.get_style_context()->add_class(CLASS_slopeDeep1);
      buttons_.add(testFrame_);
      
      toggleDraw_.set_label("draw");
      toggleDraw_.signal_clicked().connect(
                  [this]() {
                             canvas_.enableDraw (this->toggleDraw_.get_active());
                           });
      buttons_.add(toggleDraw_);
      //(End)buttons...
      
      frame_.add(scroller_);
      frame_.set_border_width(5);
      
      scroller_.set_shadow_type(Gtk::SHADOW_IN);
      scroller_.property_expand() = true;    // dynamically grab any available additional space
      scroller_.set_border_width(10);
      scroller_.add(canvas_);
      
      pStyle_ = setupStyle (testFrame_);
      
      canvas_.adjustSize();
      
      // show everything....
      this->add(twoParts_);
      this->show_all();
    }
  
  
  
  PStyleContext
  StyleTestPanel::setupStyle (Gtk::Widget const& srcWidget)
  {
    auto screen = Gdk::Screen::get_default();
    auto css_provider = Gtk::CssProvider::create();
    try
      {
        css_provider->load_from_path (lib::resolveModulePath (STYLESHEET_NAME, RESOURCE_PATH));
      }
    catch(Glib::Error const& failure)
      {
        WARN (stage, "Failure while loading stylesheet '%s': %s", cStr(STYLESHEET_NAME), cStr(failure.what()));
      }
    
    Gtk::StyleContext::add_provider_for_screen (screen, css_provider,
                                                GTK_STYLE_PROVIDER_PRIORITY_APPLICATION);
    
//  auto style = srcWidget.get_style_context();
    
    Gtk::WidgetPath path = srcWidget.get_path();
    PStyleContext style = Gtk::StyleContext::create();
    style->set_screen(Gdk::Screen::get_default());
    style->set_path(path);
    return style;
  }
  
  
  
  void
  StyleTestPanel::experiment_1()
  {
    frame_.set_label("Experiment 1... GROW");
    canvas_.xBorderSiz += 1;
    canvas_.adjustSize();
  }
  
  
  void
  StyleTestPanel::experiment_2()
  {
    frame_.set_label("Experiment 2... DUMP");
    
    cout << "xBorderSize = "<<canvas_.xBorderSiz    <<endl;
    cout << "xClass      = "<<canvas_.xObservedClzz <<endl;
    cout << "style.path: " << canvas_.xObservedPath <<endl;
    cout << "style.border.top = " << canvas_.xObservedSize <<endl;
    cout << "................\n\n";
  }
  
  
  
  /* === Canvas drawing code === */
  
  void
  Canvas::enableDraw (bool yes)
  {
    shallDraw_ = yes;
    
    // force redrawing of the visible area...
    auto win = get_window();
    if (win)
      {
        int w = get_allocation().get_width();
        int h = get_allocation().get_height();
        Gdk::Rectangle rect{0, 0, w, h};
        win->invalidate_rect(rect, false);
      }
  }
  
  void
  Canvas::adjustSize()
  {
    recalcExtension_ = true;
  }
  
  void
  Canvas::determineExtension()
  {
      if (not recalcExtension_) return;
      
      uint extH=200, extV=200;
      // ADD HERE: Code do find extension of the canvas dynamically...
      //
      recalcExtension_ = false;
      set_size (extH, extV);
  }
  
  
  bool
  Canvas::on_draw(CairoC cox)
  {
    if (shallDraw_)
      {
        uint extH, extV;
        determineExtension();
        get_size (extH, extV);
        
        auto adjH = get_hadjustment();
        auto adjV = get_vadjustment();
        double offH = adjH->get_value();
        double offV = adjV->get_value();
        
        cox->save();
        cox->translate(-offH, -offV);
        
        // draw red diagonal line
        cox->set_source_rgb(0.8, 0.0, 0.0);
        cox->set_line_width (10.0);
        cox->move_to(0, 0);
        cox->line_to(extH, extV);
        cox->stroke();
        cox->restore();
        
        //////////////////TEST drawing via Gtk::StyleContext
        {
          int marT = style_->get_margin().get_top();
          
          
          if (xBorderSiz > 1) {
//          style_->context_save();                      // <<<---does not work. Asked on SO: https://stackoverflow.com/q/57342478
            style_->add_class(slopeClassName(xBorderSiz));
          }
          
          xObservedSize = style_->get_border().get_top();
          xObservedPath = string{style_->get_path().to_string()};
          xObservedClzz = join(style_->list_classes(), " ");
          
          int height = marT + 2 * xObservedSize;
          style_->render_frame (cox
                               ,20     // left start of the rectangle
                               ,20     // top of the rectangle
                               ,50     // width of the area
                               ,height // height to fill
                               );
          // NOTE: all box-shadow effects are rendered *here*
          style_->render_background (cox
                                    ,40
                                    ,60
                                    ,80
                                    ,height
                                    );
          
          if (xBorderSiz > 1) {
//          style_->context_restore();
            style_->remove_class(slopeClassName(xBorderSiz));
          }
        }
        //////////////////TEST drawing via Gtk::StyleContext
        
        // cause child widgets to be redrawn
        bool event_is_handled = Gtk::Layout::on_draw(cox);
        
        // any drawing which follows happens on top of child widgets...
        cox->save();
        cox->translate(-offH, -offV);
        
        cox->set_source_rgb(0.2, 0.4, 0.9);
        cox->set_line_width (2.0);
        cox->rectangle(0,0, extH, extV);
        cox->stroke();
        cox->restore();
        
        return event_is_handled;
      }
    else
      return Gtk::Layout::on_draw(cox);
  }

  
  
  
  class Window
    : public Gtk::Window
    {
      StyleTestPanel demoPanel_;
      
    public:
      Window()
        : demoPanel_{}
        {
          this->add (demoPanel_);
        }
    };
  
}//namespace research



int
main (int argc, char* argv[])
{
  NOTICE (main, "*** GTK Style Experiment ***");
  
  auto guiApp = Gtk::Application::create (argc, argv);
  
  research::Window window;
  return guiApp->run(window);
}