Using native child windows in Sciter.

Sometimes there is a need of using child windows in Sciter.
For example you would like to use Scintilla editor that is implemented on Windows as a child window component.

You can do that but with the following limitations:

  1. Elements with child window attached cannot appear inside scrollable containers as windows are drawn on top of everything. Only popup element can appear on top of child windows.
  2. Such elements cannot be under CSS transformations. Windows does not support affine transformations on child windows.

For such components to be useful in Sciter we will need to solve three tasks:

  1. Let Sciter know that we want custom functionality on that particular DOM element.
  2. Create such a window and attach it to the DOM element.
  3. Provide some component specific methods for the script to manipulate the component by script code.

To accomplish all three tasks we will need to define our own native behavior.

class editor: public sciter::event_handler 
{
   // ...
public:
   virtual void attached  (HELEMENT he ) //...
   virtual void detached  (HELEMENT he ) //...
}

struct editor_factory: public behavior_factory {

  editor_factory(): behavior_factory("editor") {}

  // the only behavior_factory method:
  virtual event_handler* create(HELEMENT he) { return new editor(); }

};

// instantiating and attaching it to the global list of supported behaviors
editor_factory editor_factory_instance;

We also need to instruct Sciter on which element it shall create an instance of our class editor.

Usually that is done by declaring special element type in CSS:

editor  /* element with tag 'editor' */
{ 
   behavior: editor;  /* will have that behavior */
   display: block;    /* displayed as rectangular block */
   width: *;          /* its width and height will take */
   height: *;         /* all available space inside the container */   
}

Having the above declaration we can define the editor in our markup as:

<body>
  <editor/>
</body>

Creating window and attaching it to the DOM element

When the engine will parse <editor/> element in markup it will find style for it. That style has behavior property defined for the element
so the engine will send SC_ATTACH_BEHAVIOR notification and default SC_ATTACH_BEHAVIOR handler ( see: sciter-x-host-callback.h ) will
request chain of registered behavior factories to create instance of the event_handler for the element. As a result our editor_factory::create() method will be invoked
At the very end the engine will call our editor::attached() method to indicate that the element has the editor attached to it.

Therefore the best place to call ::CreateWindow() Windows function is the attached() method of our behavior.

class editor : 
  public sciter::event_handler
{
public:

  HWND     hwnd;
  HELEMENT self; // note: weak ref (not addrefed)

  editor(): event_handler()
            , hwnd(0)
            , self(0) 
  {}

  virtual void attached  (HELEMENT he ) 
  {
    self = he;
    dom::element el = he;
    hwnd = ::CreateWindow(
                  TEXT("Scintilla"),
                  TEXT(""),
                  WS_CHILD | WS_VSCROLL | WS_HSCROLL | WS_CLIPCHILDREN | WS_VISIBLE,
                  0, 0,
                  0, 0,
                  el.get_element_hwnd(true), // get element's host window
                  0,
                  ghInstance,
                  0);
    el.attach_hwnd(hwnd); // attach the window handler to the DOM element.
                          // after that the engine will manage window position and dimension
                          // by CSS rules 
  } 

  virtual void detached  (HELEMENT he ) 
  { 
    if(hwnd && ::IsWindow(hwnd))
      ::DestroyWindow(hwnd);
    hwnd = 0;
    self = 0;
    dom::element el = he;
    el.attach_hwnd(0);
    delete this;   // we delete the handler here as no one is using it anymore.  
  }
  ...
} 

The behavior will manage life cycle of our window: it will create the window when DOM will be created and destroy it when the element will be removed from the DOM.

Defining scripting methods

The last task left is to define methods so our script can do something meaningful with the window.

In order to do that we need to define handle_scripting_call() in our behavior but instead of doing it that literally we will use BEGIN_FUNCTION_MAP/END_FUNCTION_MAP that provide
handle_scripting_call implementation for us:

class editor : 
  public sciter::event_handler
{
public:

  HWND     hwnd;
  HELEMENT self; // note: weak ref (not addrefed)

  editor(): event_handler()
            , hwnd(0)
            , self(0) 
  {}

  virtual void attached  (HELEMENT he ) { ... } 
  virtual void detached  (HELEMENT he ) { ... }

// scripting methods bindings
  BEGIN_FUNCTION_MAP
    FUNCTION_0("getText",get_text) // getText()
    FUNCTION_1("setText",set_text) // setText(text:string) 
  END_FUNCTION_MAP

  sciter::value get_text() {
    std::wstring text;
    // GetWindowText(hwnd) & friends here
    return sciter::value(text);
  }  

  sciter::value set_text(const sciter::value& text_val) {
    std::wstring text = text_val.get(L"");
    // SetWindowText(hwnd) & friends here
    return sciter::value(); // returns undefined value, a.k.a. void
  }  
}

This way we have defined our behavior that exposes two methods that we can use in script:

<script type="text/tiscript">
function self.ready() {
  var elEditor = $(editor);
  elEditor.setText("Hello world!"); // calling our native method
}
</script>
<body>
  <editor/>
</body>

In reality you probably will have more native methods defined. Just don’t forget to add their bindings to the FUNCTION_MAP.

And see this discussion about wrapping Scintilla editor.

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