OpenEuphoria

Win32Lib Update

• Posted by David Cuny <dcuny at LANSET.COM> Oct 23, 1998
• 917 views

I've just sent the latest version of Win32Lib to Robert. It includes a
number of bug fixes, as well as some new features.

As with the last update, this version will cause your old programs to break.
I try to keep this to a minimum, but sometimes it becomes clear that changes
have to be made. In this case, it's with the onPaint event.

This post is long, to explain a bit about Windows graphics, and how Win32
handles them, and what brought about the change. All this is subject to
change, but I figured that some sort of explanation would be helpful (we'll
see).

Prior versions of the event pass no parameters; the function prototype now
looks like:

    Window_OnPaint( integer x1, integer y1, integer x2, integer y2 )

As you might imagine, the procedure now receives the area of the window that
needs to be updated. This is sometimes called the "damaged region" of the
window. Windows can be "damaged" by resizing, being obscured, and so forth.

Anyone who's tried it knows that programming Windows graphics is a bit
different than programming DOS graphics. In DOS, things you write to the
screen remain there. In Windows. areas of the screen can be "damaged" and
require repainting. So it's the job of the onPaint routine to repair any
damage to the window.

That means that onPaint needs to know how to draw *any* part of the window,
on demand. This usually requires that applications be written a bit
differently.

Prior versions forced the *entire* window to be updated with the call:

    repaintWindow( iWin )

As you can imagine, this is more than a bit inefficient. I've added a new
procedure:

    updateRect( iWin, integer x1, integer y1, integer x2, integer y2 )

No surprise here - the parameters that it passes are those received by the
onPaint procedure. I'm doing more than simply attaching parameters to the
onPaint routine, though. Windows had *always* passed a clipping window to
onPaint. It just happened that Win32Lib (though repaintWindow) always forced
it to be the same size as the window, so it could be ignored.

Note the words "clipping window" - this means that within the onPaint event,
there is no way to put graphics *outside* the clipping window (that's why
it's called a clipping window - graphics are clipped to the bounds of the
rectangle).

All this may seem a bit abstract, so I've created a couple of demos to show
off the features. One particular problem I encountered while writing the
code may help explain the issue. But first, some background (and details on
Win32Lib's inner workings):

If you have the 0.13 alpha version of Win32Lib, there is a tile demo (ex17)
that shows off the new createMonochromeBitmap() feature (which doesn't work
in NT, sorry). When a bitmap is clicked, the tile is "turned over". This is
how this is accomplished:

1. The array holding the bitmaps is updated.
2. repaintWindow() is called, to force the window to be redisplayed.
3. repaintWindow scans through the array, and redraws the all the bitmaps.

So the only routine that knows how to write to the window is onPaint.

You may notice that there is a bit of flickering as this happens.

When repaintWindow() is called, it tells Windows that the *entire* window is
damaged (see a couple of paragraphs back).

One of the things that Windows does automatically in onPaint is to repaint
the damaged portion of the window using the window's background color. Since
repaintWindow said that the *entire* window was damaged, the entire window
is erased, and you see a flash of white.

Then the onPaint routine is called, and it has to redraw *all* the tiles in
the window. This happens *every time* it needs to update the window. Very
inefficient, and very slow.

In the 0.14 version of Win32Lib, I've re-written the code to use
repaintRect() to pass the location of the bitmap that needs to be repainted.
Since only that portion of the window is erased, only that portion needs to
be redrawn. The result is a *much* cleaner.

Enough background. Both of the demos are modeled around the above process.
The only routine that does any writing to the window is the onPaint routine.
The other routines update data structures, and then tell onPaint what part
of the window needs to be drawn by calling updateRect.

Now onto the problem: I needed to write information to a "status line".
Initially, I just placed the line:

    setPosition( Win, 1, 1 )
    wPrintf( Win, "Score: %d", {score} )

into the onPaint routine. Much to my suprise, the text *didn't* show up.
That's because it didn't fall any of the the clipping rectangles that was
passed to onPaint. Since the text fell outside the clipping region, Windows
didn't bother to display it. I finally hacked a solution, by adding this
call *outside* of onPaint, whenever I wanted to redisplay the status line:

    repaintRectangle( Win, 1, 1, 200, 20 )

This created a call to onPaint that "uncovered" the score.

There are better solutions to the above scenario, but I thought that people
might be interested in getting some feel for what graphics in Win32Lib looks
like in v0.14. I'm certain things will become better as time goes on...

Well, now people should have some idea why I haven't tried writing a
Win32Lib tutorial myself... 

-- David Cuny