[AD] Tr: Allegro 5.0's interface with Windowing systems

["Eric Botcazou" <ebotcazou@xxxxxxxxxx>]

----- Original Message -----
From: Jason McKesson <jmckesson@xxxxxxxxxx>
To: <ebotcazou@xxxxxxxxxx>
Sent: Thursday, March 21, 2002 5:11 AM
Subject: Allegro 5.0's interface with Windowing systems


Hello, I'm an Allegro user, and I have a suggestion for the next release of
Allegro. I understand that you are responsible for the Win32 port of
Allegro, and my suggestion was referred to you by Bob.

One problem I have with Allegro is creating useful tools using Allegro's
drawing capabilities. I want to use MFC to write these tools rather than the
(rather poor) GUI that Allegro provides. But, something like a tilemap
editor is virtually impossible to implement in Allegro. Allow me to clarify
the problem.

The problem is message processing: Allegro wants to use its own message
processing loop. MFC wants to use its own message processing loop.
Obviously, only one can function at a time. Therefore, the only way to draw
into an MFC window with Allegro is to use the horrendously slow
"blit_to_hdc" method.

There is a solution to this delima: enter into a cooperative relationship
with the user.

The user will create a HWND. If Allegro needs to change some of the creation
parameters before creation, then there should be an appropriate function to
allow Allegro to modify the CREATESTRUCT. In the window's OnCreate handler,
Allegro should be called with the HWND to bind that HWND to Allegro's
system. This function would be analogous to a call to "alCreateDisplay" (in
the new graphics API). It would also replace that call. The returned BITMAP
refers to the window of that HWND.

For any message that Allegro needs to know about, there should be a function
avaliable that will pass the message data along to Allegro. For example, if
Allegro needs to process WM_SIZE messages on that HWND, then the user
program must process WM_SIZE message and call "alWndOnSizeMsg" with the
HWND and the new width/height. I don't know exactly which message Allegro
needs to know about, but I'm sure you do.

The major change in this (besides creation and getting the messages in a
different fashion) is that Allegro must allow for window resizing. Now, if
the window was created by Allegro, then it is perfectly reasonable for
Allegro not to appreciate window resizing and disallow it. However,
user-created HWNDs should allow for window resizing. If you've bound the
HWND to either DirectX or OpenGL, neither of them are particularly upset at
a resize request, so the underlying code need not change much. The only
thing is that the user must understand that the display BITMAP's size can
change based on the window resizing.

Note that virtually all of this likely applies to X-Windows. It may require
a few different function calls, but you can probably create the same effect
under X as you can under Win32.

This will solve the one major hurdle I have in working with Allegro. As it
stands now, I can't really make functioning WYSIWYG tools in Allegro because
I can't use the same rendering facilities in a windowed tool that I can in a
game.

Thank you.
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