Extending WndTabs – The WndTabs SDK

The new WndTabs 'Addons' menu with one addon loaded

The WTSDK_Samp Addon


The WndTabs SDK allows Visual C++ addins to interface with WndTabs, adding
new capabilities to the WndTabs tabs.  Through the SDK, you can add new
commands to the tabs, and also alter the way the tabs look.  Addins that
enhance WndTabs through the SDK are called WndTabs addons.

The SDK is supported by version 3.0 of WndTabs (get
it here

If you aren’t familiar with the WndTabs addin, you can learn more
about it here and here.

Creating a WndTabs Addon

WndTabs addons must be registered with the AddInComm
, as WndTabs uses the AddInComm’s dynamic discovery and messaging
facilities to communicate with the addons.  After registering with
AddInComm, the InitWndTabsIntegration
function is used to initialize the SDK.  Both procedures should be performed in your addin’s

STDMETHODIMP CDSAddIn::OnConnection(IApplication* pApp,
                                    VARIANT_BOOL bFirstTime,
                                    long dwCookie,
                                    VARIANT_BOOL* OnConnection)
 // Register with AddInComm
 m_hAddin = AICRegisterAddIn("MyAddon",

 // Register with WndTabs
                        WndTabs_Ev_WindowChanged | WndTabs_Ev_TabClicked););

The AICRegisterAddIn call adds your addin to AddInComm’s active addin
database.  In the above example, the add-in is registered with the name
"MyAddon", with the version number 1.0.5.  The AddInCallback
function is designated as the AddInComm message handler.

InitWndTabsIntegration initializes the WndTabs SDK.  It must know the
AddInComm name your addin is using, as well as other information regarding
specific SDK functionality, such as which commands your addon supports. 
These parameters will be discussed in further detail below.

To clean up resources, and properly unregister from WndTabs and AddInComm,
the following code should appear in an Addon’s OnDisconnection method:

EndWndTabsIntegration();      // Unregister from WndTabs
AICUnregisterAddIn(m_hAddin); // Unregister from AddInComm

We’re almost there – just one thing left to do:  The WndTabs SDK code
has to be hooked into your AddInComm message handler, allowing it to
intercept SDK related messages.  In the OnConnection function, we specified

as the callback function.   A skeleton for this function
would be:

// callback for AddInComm
int AddInCallback(LPCTSTR pCmd)

 int iRetVal;
 if ((iRetVal = WndTabsInt_Callback(pCmd)) != -1)  // call the SDK  
  return iRetVal;

 // do any other processing here

 // -1 should be returned if you didn't handle the command
 return -1;

It is an AddInComm convention to return -1 if you don’t handle the specified
command.  For non-SDK commands, the WndTabsInt_Callback
function returns just that.  This means that if your addin doesn’t implement any AddInComm
commands of its own, you can
pass WndTabsInt_Callback directly to the AICRegisterAddIn
function to save
yourself the trouble of writing a callback function.

Adding New Commands To WndTabs

Commands for the WTSDK_Samp addon, as displayed in a tab context menu

Up to this point, we’ve seen how to create a skeleton addon that doesn’t
actually do anything.  It’s time to add some functionality.

One of the things that addons can do is to add new commands to
WndTabs.  These commands are displayed under the Addons sub-menu (which is
available, by default, under both the tab context menu and the main WndTabs menu).

Declaring Your Commands And Command Handler

For each command you want to add, you must supply a WTSDK_CommandDef

// from the SDK headers
struct WTSDK_CommandDef
 int     iCmd;       // the identifier for your command
 LPCSTR  pszName;    // the display name for your command
 int     idBmpRes;   // the resource id for the menu bitmap (or -1)
 WTSDK_UIUpadateFlags UIUpdateFlags;

// from WTSDK_Samp
WTSDK_CommandDef Commands_For_WT[] =
 { idCmdShowDialog,
   "Show WTSDK_Samp Dialog",
   UI_AlwaysAvailable },
 { idCmdEnable,
   "Enable Transforms",
   UI_UseCallback     },
 { idCmdShowContext,
   "Show Command Context",
   UI_AlwaysAvailable },
 { idCmdFileInfo,
   "Show File Information",
   UI_MustHaveFile    }

The pszName and idBmpRes fields are self explanatory. 
The iCmd field should specify a unique identifier for each command. 
This identifier is passed back to your command handler, just as Windows passes message
identifiers to your program’s message handler.  The UIUpdateFlags
parameter specifies when the command should be enabled/disabled.  But we’ll
get into that in just a bit.

You also need to supply a command handler callback.  The handler looks
like this:

void OnWTCommand(int iCmd,
                 const WTSDK_CommandContext *pCmdContext)
 switch (iCmd)
  case idCmdEnable :
  cfg_bEnabled = !cfg_bEnabled;

   // unknown command!

The Command Context

Before any WndTabs command (either internal or Addon supplied) is executed, WndTabs
creates a command context object.  This object includes invaluable
information about the tab/file that is associated with the command.  This is the
tab that you right-clicked on (if you execute a command from the tab context
menus), or the active tab (if you use a keyboard shortcut or a non-tab menu). 
Note that it is still legal to use a keyboard shortcut when there are no windows
at all!  The command will still be issued, but the command context will
reflect the fact there is no associated tab/file.

struct WTSDK_CommandContext
 /* set to size of this structure */
 UINT    cbSize;

 BOOL    bHasDoc;
 BOOL    bHasFile;
 BOOL    bIsTextWindow;
 BOOL    bIsActiveWindow;
 BOOL    bIsGroupOperation;
 HWND    hWnd;
 char    szFullPath[MAX_PATH];

 // DevStudio automation
 CComPtr<IGenericWindow> pWindow;

 CComPtr<IGenericDocument>  pDoc;

A WTSDK_Samp command context dialog for the AboutDlg.cpp file

Again, most of the WTSDK_CommandContext fields are self explanatory. 
The following is a brief overview of a few of the contexts you can run into:


bHasFile True – This is a normal file window
False – This is a non file window (e.g. the
"Disassembly" window)/a window of a file that hasn’t been
saved before/command issued with no open windows
bHasDoc True – This window has editable content (i.e. a
text file or resource file)
False – This is a non editable window (e.g. the
"Disassembly" window)/command issued with no open windows
bIsTextWindow True – A text window
False – A non text window, such as a resource file
or a docked DevStudio window (i.e. "Disassembly",
"Output", etc.)
bIsGroupOperation True – The user clicked on the shared part of a
group tab (WndTabsExt only)
False – The user clicked on a non group tab or on a
specific file within a group tab

UI Updates

The last piece in the puzzle is the UI update.  It is up to you to tell
WndTabs when your command should be enabled or disabled.  For your
convenience, the WndTabs SDK defines the WTSDK_UIUpadateFlags
enumeration, which is passed in the command’s WTSDK_CommandDef

enum WTSDK_UIUpadateFlags
 UI_AlwaysAvailable     = 0,

 // was already saved at least once, i.e. not a new 
 // text window 
 UI_MustHaveFile        = 1,

 // any editable window - windows such as "Disassembly" 
 // don't have a doc 
 UI_MustHaveDoc         = 2,

 // same as above, but must be a text document (for instance, 
 // not a resource) 
 UI_MustHaveTextDoc     = 4,

 // at least one window must be open
 UI_MustHaveOpenWindows = 8,

 // command applies only to active windows 
 UI_MustBeActiveWindow  = 16,

 // call user-defined UI update callback
 UI_UseCallback         = 128

You can pass any combination of flags:

// enable only if has a document and is the active window
(UI_MustHaveDoc | UI_MustBeActiveWindow)

// enable/disable based on file availability, then call 
// user callback
(UI_MustHaveFile | UI_UseCallback)

The user callback function for UI updates is an optional function
that you can pass to the SDK while registering your addon.  This function
is very similar to a function that you would write to handle MFC’s ON_UPDATE_COMMAND_UI
message.  For example, this is the UI handler
implemented by SDK sample:

// This is a sample of a custom UI handler (used only for the 
// "Enable Transformation" command).
// The handler sets a checkmark for the command based on the current 
// configuration settings.
void OnWTCommandUpdateUI(int iCmd,
                         CCmdUI *pCmdUI,
                         const WTSDK_CommandContext *pCmdContext)
 // only the idCmdEnable command requested UI notifications
 ASSERT(iCmd == idCmdEnable);


Tab Morphing

Example of tab transformations Example of tab transformations

The most interesting feature of the SDK, in my opinion, is the ability to
transform the tabs themselves.  An SDK addon has access to the following
tab attributes:

  • The Tab Text – You can change the text as well as the text color.
  • The Tab Icon – You can change/replace the icon.
  • The Tab Overlay Icon – The overlay icon is merged with the regular
    icon before the tab is drawn.  For example, the tab numbers are

Tab transformations require that the
WndTabsExt component be enabled.

In the above pictures you can see a few of these transformations:

Icon Transform
Left Picture The .cpp extension was changed to .cxx
The color was changed
A new icon for .cpp files
A red border for read-only files
Right Picture The asterisk was removed
The color was changed
A new icon for .cpp files The asterisk was added as an overlay

Note the use of an "overlay" for the asterisk icon (right
picture).  Although you can change the actual icon,
overlaying is usually achieved by modifying the overlay icon (which usually holds the tab number
image).  Changing the overlay icon will ensure that the overlay is unaffected when other addons modify the actual icon.

Transformation are preformed in two stages:

  1. The change stage – In this stage, addons a expected to make any
    destructive changes, such as totally replacing the text or icon.
  2. The modify stage – In this stage, addons are expected to make modifications
    to the current text/icons.

Although the above guidelines cannot be enforced, all addons are expected to

The Tab Modification Function

The tab modification callback (which was passed to the SDK during InitWndTabsIntegration
call) looks like this:

void OnTabUpdate(WTSDK_TabUpdateInfo *pTabUpdateInfo,
                 const WTSDK_CommandContext *pCmdContext)
 // find out some stuff about the tab's file
 const char * const pLastDot =
  strrchr(pCmdContext->szFullPath, '.');

 bool bIsCpp =
  (pLastDot && (stricmp(pLastDot, ".cpp") == 0));


 if (pTabUpdateInfo->stage == WTSDK_TabUpdateInfo::change)
  // the "change" stage - perform any operation 
  // that totally replaces texts or icons
  // the "modify" stage - perform any operation that 
  // makes alterations to existing texts or icons

Like other callbacks, you have access to the command
.  However, the actual information about the tab is passed in
the WTSDK_TabUpdateInfo structure:

struct WTSDK_TabUpdateInfo
 UINT cbSize; // Must be set to sizeof(WTSDK_TabUpdateInfo)

 // see explanation here
 enum { change, modify } stage;

 // == Text on Tab ==
 // the number (0 based index) of the tab - notice,
 int iTabNumber;
 //   however, that the text indexes shown to the
 //   user start at 1 (i.e. TextIdx==iTabNumber + 1)

 // the text before the file name (i.e. tab number) - see picture
 char szPrefix[256];

 // the text that belongs to the tab's entire group (the file 
 // name) - see picture
 char szBase[512];

 // the text that is different for each tab in the group (the 
 // extension) - see picture
 char szSuffix[256];

 // These are the texts without alterations - DO NOT CHANGE
 const char *pszOrigPrefix, *pszOrigBase, *pszOrigSuffix;

 // == Colors ==
 COLORREF    crTextColorSel;     // when tab is selected
 COLORREF    crTextColorNotSel;  // when tabs isn't selected

 // == Icons ==
 wt_auto_icon  hIcon;
 wt_auto_icon  hIconOverlay;

The text parts of a tab

In order to change the text, you may modify szPrefix, szBase
and szSuffix.  The text color is defined by crTextColorSel
and crTextColorNotSel.  The icons (regular and overlay) are
accessed through the hIcon and hIconOverlay variables.

in mind that the text in the tab info object might not correspond to the
original file name.  For instance, for .cpp files, szSuffix
should be ".cpp", however, any addon may change this text.  Even
the pszOrigSuffix variable that holds the original value might not
have ".cpp" as it’s value, because the user might choose not to
display extensions on the tabs!  If you need to access the file’s name, use
the command context object.


WndTabs Events

Another service provided by the SDK is WndTabs events.  To get access to
event, you may optionally pass an event handler to the SDK initialization
function.  This function will be called whenever one of the following
events occurs:

WndTabs_Ev_WindowChanged Called whenever the active window is changed (or if the last window is closed). 
The extra parameter to this event is the HWND of the new window (or NULL if there are no open windows).

NOTE: If the user changes/opens/closes windows very quickly (e.g. by using Close All Windows or opening many files at once), an event might
not be generated for every single window activation/deactivation!

WndTabs_Ev_TabClicked Called whenever a user left-clicks on a tab. Note that this does not necessarily mean that a window change will occur. 
The extra parameter to this event is the number of the tab that was clicked (or -1 if there are no open windows).

The SDK Sample Addon (WTSDK_Samp)

You know what they say: A sample’s worth a thousand articles.  And I say
that they’re right!

The SDK comes with a sample addon – WTSDK_Samp.  The sample demonstrates
everything you can do with an addon – text transformations, commands, and UI
callbacks.  It also demonstrates proper AddInComm registration.  In
short – it’s a good place to start.


Tips For Writing Addons

If you’re thinking about writing an addon, here are a few pointers to get
you started:

  • The source code for WndTabs is available for download.  You can
    compile a debug build that will help you track bugs much more quickly.
  • Your addon is just another DevStudio addin.  For tips on debugging
    addins, check the WndTabs online help under the "Compiling and
    Debugging" topic.
  • If you mix Debug builds of addons with a Release build of WndTabs (or visa
    versa), your addon dialogs might not appear centered on the screen.  This
    is normal
    .  The problem will go away when create a release build.
  • Support is just an e-mail


If you install and play around with the SDK and its sample, you will quickly
realize that the sky is the limit!  Everything from unique icons to hooking
the tabs into your favorite version control system
is now possible… 
Just write a WndTabs addon!


Download the SDK + Sample Addon (88kb) from the WndTabs web site

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