Monday, October 29, 2007

New poll on the lazarus site about Windows versions

Lately I have been trying to fix recompiling the Lazarus (needed to install components) from the IDE. On windows 2000 and higher, using .rc files is working OK if windres is not on the path, but on windows 98 there are still some problems.

Marc has done a large graphic rewrite in Lazarus 0.9.23 and he also noticed that there are noticeable difference between Windows 98 and Windows XP.

I wondered if there still many people using Windows 98 and Windows ME for Lazarus development or as target for LCL application. Therefore I created a new poll on the Lazarus website, asking people about the oldest Windows version is, that they use for Lazarus development.

Currently when we program on the win32 interface we try to use only functions available in windows 95, or provide a fall back if we want to use a function not available on windows 95. Some features like graphics, Unicode support, the shell provided by cmd32.exe and the availability of console (used for the debugger) are better and easier in Windows 2000 and later. So it would be nice if we could restrict ourselves to these newer Windows versions.

Personally, I don't think we can drop support for windows 98 yet, but I doubt anybody is using Windows 95 to program with Lazarus. Let us know where you stand and cast your votes in the poll. This poll is about the OS you use for Lazarus, a future poll may be held about the Windows versions you want your developed applications to run on.

Note: people who don't use Lazarus on Windows, don't need to vote.

Sunday, October 28, 2007

How TPageControl tab switching in designer has been solved

I think most users who used TPageControl in windows ide suffered from the inability to stitch its Tabs by clicking them in the designer. Indeed, the gtk ide had no such bug while the windows one had. I got annoyed by the fact too and as result I started my research of the problem.

My first assumption was that somewhere a csDesigning (you know that usual "if csDesigning in BlaBla.ComponentState" ;) ) condition was written and I spent much time (searching code) to prove myself that I am wrong.

Ok, if I am wrong (I thought) then it is by design or by the designer :) So I started my research of how the win32 designer works. Usually my research consists of Alt+F7 in Far manager for some search key (in this case for 'designer') and if Alt+F7 doesn't help, then in debugging the code. I suppose on that occasion I had been satisfied by search in files. First of all I found 'TWin32WidgetSet.GetDesignerDC' method and later I've checked that this method is indeed what I searched for. Look at TDesigner.DrawDesignerItems and you'll find that yourself.

So, I've known the enemy by sight :) If you notice GetDesignerDC creates a visually transparent window over WindowHandle and returns the Device Context for that overlay window. The Device Context is not a interesting thing for us, but the overlay window is. That overlay window is placed on top of a form (and all child controls). And the most interesting thing in that overlay window is the window procedure OverlayWindowProc.

Inside OverlayWindowProc we can find that overlay window easts all messages except WM_KEYFIRST..WM_KEYLAST, WM_MOUSEFIRST..WM_MOUSELAST and that bunch of messages it redirects to the parent (look at Windows.GetParent(Window)). If you look at TDesigner.DrawDesignerItems then you'll know that the Parent of OverlayWindow is the Form. So nothing wondering now that the PageControl Tabs cannot be switched in designer - PageControl gets no clicks (they are caught by our overlay window).

Hmm ... I thought about a solution. The first thing that flashed through my mind was sending those mouse clicks to the underlying control. But it is so easy to forget about some messages or make other errors if you want to emulate windows behaviour. So I rejected that way as defective. Another way is to make some parts of our overlay window transparent for mouse. Windows has a special message WM_NCHITTEST to check what a given coordinate means. And a window can return HTTRANSPARENT as result of a message to indicate that message must be sent to the underlying window (so this point is transparent for the window).

As result the whole solution consisted of handling WM_NCHITTEST in OverlayWindowProc and return HTTRANSPARENT if underlying control wanted mouse messages for that point at design time. I've added a new method GetDesignInteractive to TWSWinControl.

class function GetDesignInteractive(const AWinControl: TWinControl; AClientPos: TPoint): Boolean;

Now I had a method to check, but of course I needed the implementation of that method for TPageControl (which checked that mouse is over control Tabs). So I've added TWin32WSCustomNotebook.GetDesignInteractive, rebuilt the win32 ide and hurray - I switched PageControl tabs in designer w/o problems.

You can look at implementation in revisions: 12245, 12620 (method has been renamed).