message_crackers.md

windowsx.h message crackers cheatsheet

This will be helpful for implementing own GUI framework

Quick reference table

Message	Callback function signature
WM_CREATE	BOOL OnCreate(HWND hWnd, LPCREATESTRUCT lpcs);
WM_SIZE	void OnSize(HWND hWnd, UINT state, int x, int y);
WM_DESTROY	void OnDestroy(HWND hWnd);
WM_PAINT	void OnPaint(HWND hWnd);
WM_LBUTTONDOWN	void OnLButtonDown(HWND hWnd, BOOL fDoubleClick, int x, int y, UINT keyFlags);
WM_LBUTTONUP	void OnLButtonUp(HWND hWnd, int x, int y, UINT keyFlags);
WM_COMMAND	void OnCommand(HWND hWnd, int id, HWND hwndCtl, UINT codeNotify);
WM_KEYUP	void OnKeyUp(HWND hWnd, UINT vk, int cRepeat, UINT flags);
WM_KEYDOWN	void OnKeyDown(HWND hWnd, UINT vk, int cRepeat, UINT flags);
WM_MOUSEMOVE	void OnMouseMove(HWND hWnd, int x, int y, UINT keyFlags);
WM_DRAWITEM	void OnDrawItem(HWND hWnd, LPDRAWITEMSTRUCT lpdis);
WM_MEASUREITEM	void OnDrawItem(HWND hWnd, LPDRAWITEMSTRUCT lpdis);
WM_NOTIFY	void OnNotify(HWND hWnd, int idFrom, LPNMHDR pnmhdr);

Detailed list

WM_CREATE

BOOL OnCreate(HWND hWnd, LPCREATESTRUCT lpcs);

Should return the success status of window initialization of type BOOL. If WM_CREATE returns FALSE, window creation will be considered unsuccessful.

Parameters description

Symbol	Argument	Description
LPCREATESTRUCT lpcs	dynamic cast of lParam	Pointer to window creation data structure

Snippets

HANDLE_MSG(hWnd, WM_CREATE, OnCreate);

OnCreate(HWND hWnd, (LPCREATEPARAM)lpcs);

OnCreate(HWND hWnd, reinterpret_cast<LPCREATESTRUCT>(lparam));

WM_SIZE

void OnSize(HWND hWnd, UINT state, int x, int y);

Parameters description

Symbol	Argument	Description
UINT state	static cast of wParam	See MSDN
int x	LOWORD lParam	Updated client area width
int y	HIWORD lParam	Updated client area height

Snippets

HANDLE_MSG(hWnd, WM_SIZE, OnSize);

OnSize(HWND hWnd, (UINT)wParam, LOWORD(lParam), HIWORD(lParam));

OnSize(HWND hWnd, static_cast<UINT>(wParam), static_cast<int>(LOWORD(lParam)), static_cast<int>(HIWORD(lParam)));

WM_DESTROY

void OnDestroy(HWND hWnd);

Parameters description

None

Snippets

HANDLE_MSG(hWnd, WM_DESTROY, OnDestroy);

OnDestroy(HWND hWnd);

OnDestroy(HWND hWnd);

WM_PAINT

void OnPaint(HWND hWnd);

Parameters description

None

Snippets

HANDLE_MSG(hWnd, WM_PAINT, OnPaint);

OnPaint(HWND hWnd);

OnPaint(HWND hWnd);

WM_DRAWITEM

void OnDrawItem(HWND hWnd, LPDRAWITEMSTRUCT lpdis);

Parameters description

Symbol	Argument	Description
LPDRAWITEMSTRUCT lpdis	reinterpret cast of lParam	Pointer to item being drawn

Snippets

HANDLE_MSG(hWnd, WM_DRAWITEM, OnDrawItem);

OnDrawItem(HWND hWnd, (LPDRAWITEMSTRUCT)lParam);

OnDrawItem(HWND hWnd, reinterpret_cast<LPDRAWITEMSTRUCT>(lParam));

WM_MEASUREITEM

In dialogs called before WM_INITDIALOG. Make sure you have your handler registered.

void OnMeasureItem(HWND hWnd, LPMEASUREITEMSTRUCT lpMeasureItem);

Parameters description

Symbol	Argument	Description
LPMEASUREITEMSTRUCT lpMeasureItem	reinterpret cast of lParam	Pointer to structure describing the item being measured

Snippets

HANDLE_MSG(hWnd, WM_MEASUREITEM, OnMeasureItem);

OnMeasureItem(HWND hWnd, (LPMEASUREITEMSTRUCT)lParam);

OnMeasureItem(HWND hWnd, reinterpret_cast<LPMEASUREITEMSTRUCT>(lParam));

WM_NOTIFY

void OnNotify(HWND hWnd, int idFrom, LPNMHDR pnmhdr);

Parameters description

Symbol	Argument	Description
int idFrom	static cast of wParam	id
LPNMHDR pnmhdr	reinterpret cast of lParam	id

Snippets

HANDLE_MSG(hWnd, WM_NOTIFY, OnNotify);

OnNotify(HWND hWnd, (int)wParam, (LPNMHDR)lParam);

OnNotify(HWND hWnd, static_cast<int>(wParam), reinterpret_cast<LPNMHDR>(lParam));

Style guide

For unifying the order which message handling follows it might be helpful to order them by message macro values

1. WM_CREATE
2. WM_SIZE
3. WM_PAINT
4. ...
5. WM_DESTROY

Examples

C (Plain WinApi)

...

BOOL OnCreate(HWND hWnd, LPCREATESTRUCT lpcs) {
  /* Return TRUE if window initialization succeed, otherwise return FALSE */
  return TRUE;
}

void OnPaint(HWND hWnd) {
  PAINTSTRUCT ps = { 0 };
  
  HDC hdc = BeginPaint(hWnd, &ps);
  Ellipse(hdc, 0, 0, 50, 50);
  EndPaint(hWnd, &ps);
}

void OnDestroy(HWND hWnd) {
  /* Quit application if the window destroys */
  PostQuitMessage(0);
}

/* Static message handling procedure */
LRESULT CALLBACK WndProc(HWND hWnd, UINT message, WPARAM wParam, LPARAM lParam) {
  switch (message) {
    HANDLE_MSG(hWnd, WM_CREATE, OnCreate);
    HANDLE_MSG(hWnd, WM_PAINT, OnPaint);
    HANDLE_MSG(hWnd, WM_DESTROY, OnDestroy);
  }

  return DefWindowProc(hWnd, message, wParam, lParam);
}

...

C++ (i.e. OOP GUI framework)

class Wnd {
protected:
  virtual BOOL OnCreate(LPCREATESTRUCT);
  virtual void OnPaint();
  virtual void OnDestroy();
  
  virtual LRESULT CALLBACK UserWndProc(UINT message, WPARAM wParam, LPARAM lParam) {
    return ::DefWindowProc(hWnd_, message, wParam, lParam);
  };
  
  HWND hWnd_;

private:
  static LRESULT CALLBACK StaticWndProc(HWND, UINT, WPARAM, LPARAM);
};


/******************
 *  InheritedWnd  *
 ******************/
 
// Define a custom message code
#define WM_INHW_CUSTOMMESSAGE WM_USER + 1

// Define a custom data type for the custom message
struct _tagCUSTOMMESSAGE {
  int x;
};
typedef struct _tagCUSTOMMESSAGE CUSTOMMESSAGE, *PCUSTOMMESSAGE;


class InheritedWnd : public Wnd {
protected:
  void OnCustomMessage(PCUSTOMMESSAGE);

  virtual LRESULT CALLBACK UserWndProc(UINT, WPARAM, LPARAM) final override;
};

BOOL Wnd::OnCreate(LPCREATESTRUCT lpcs) {
  // Use internal field instead of hWnd parameter
  (void)hWnd_;
  
  return TRUE;
}

void Wnd::OnPaint() {
  PAINTSTRUCT ps{};

  HDC hdc = ::BeginPaint(hWnd_, &ps);
  ::Ellipse(hdc, 0, 0, 10, 10);
  ::EndPaint(hWnd_, &ps);
}

void Wnd::OnDestroy() {
  ::PostQuitMessage(0);
}

LRESULT CALLBACK Wnd::StaticWndProc(HWND hWnd, UINT message, WPARAM wParam, LPARAM lParam) {
  Wnd* wnd = ...; // Somehow obtain the window object pointer
  
  switch (message) {
    case WM_CREATE:
      return wnd->OnCreate((LPCREATESTRUCT)lParam);
      break;
    case WM_PAINT:
      wnd->OnPaint();
      return 0L;
      break;
    case WM_DESTROY:
      wnd->OnDestroy();
      return 0L;
      break;
  }
  
  if (wnd) {
    return wnd->UserWndProc(hWnd, message, wParam, lParam);
  }
  
  // If its not possible to obtain Wnd*, handle message to system:
  return ::DefWindowProc(hWnd, message, wParam, lParam);
}

void InheritedWnd::OnCustomMessage(PCUSTOMMESSAGE pCustMsg) {
  (void)(pCustMsg->x);
}

LRESULT CALLBACK InheritedWnd::UserWndProc(UINT message, WPARAM wParam, LPARAM lParam) {
  switch (message) {
    case WM_INHW_CUSTOMMESSAGE:
      OnCustomMessage((PCUSTOMMESSAGE)lParam);
      return 0L;
      break;
  }

  return ::DefWindowProc(hWnd, message, wParam, lParam);
}

For more practical examples you can check out these projects

• Taiga (especially, Windöws) by erengy — Lightweight anime tracker for Windows built on top of own Windows GUI framework
• Panit.ent — Simple raster graphics editor/painter
• PaniView — Simple image viewer