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1992-05-06
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(overscan.README)
Overscan
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By Ari & Dov Freund - 20/11/87
The Purpose Of Overscan
Under Kickstart V1.2 it is possible for Amigas using a European PAL display
to have screens and windows as high as 256 lines in non-interlace mode, and
512 lines in interlace mode. This is an increase of about 25% over the
workspace available on American machines. Unfortunately, there are quite a
few commercial programs, written mainly by Americans who don't bother to
utilize this new feature, which open their screens/windows to a maximum of
200 lines, depriving European machine users of the extra space.
Enter Overscan. Overscan patches Intuition such that screens/windows will
open to their full height. You are not required to modify the application
program in any way. Just install Overscan once and it will remain in effect
until you remove it or restart the system. Any program run after Overscan
has been installed will have large screens/windows. Note that with Overscan,
screens will actually open with more lines, whereas windows will open with
their intended height but will be resizable to the maximum height possible.
Using Overscan
To install Overscan type: overscan
To remove Overscan type: overscan delete
Programs Incompatible With Overscan
Let us start out by saying that most programs will be enhanced by Overscan
but not all. The main reason for this is that Overscan is transparent to
the application program. There is no way for Overscan to "tell" the
application program that it has more lines. A program may find out how many
display lines it has by asking Intuition for this information. In that case
Intuition would inform the program of the extra lines and they would be put
to good use. This is usually the case for windows with a sizing gadget, as
the size of the window may change and the program must continually update
its information about the window's size. Alternatively, a program may rely
on the fact that under normal conditions the size of its display will not
change, and thus will not bother to check the actual height of its
screen/window. The extra lines will be provided by Overscan but the
application program will not know of their existence and will not take
advantage of them. This is usually the case for screens and for windows
without a sizing gadget. (DeluxePaint is an example of such an
application.)
In addition, not always is it possible to add lines to the screen/window.
Screens/windows may use for their display a custom bitmap. Using a custom
bitmap means that the program opening the screen/window has already set
aside the memory needed for the display of the screen/window. If Overscan
were to add lines to the screen/window there would be no memory to hold the
display for these lines, the end result being a session with the guru.
Also, if the intended height for the screen/window is something other than
the USA maximum height this would probably indicate that the program does NOT
want any extra lines, and Overscan will not interfere.
Windows in particular may cause some additional trouble because windows
open in screens. There are two types of screens on the Amiga: the Workbench
screen and custom screens. The difference is that the Workbench screen
(when open) is always open to the maximum height possible whereas the
height of custom screens is determined by the program that opened them. It
wouldn't make sense to allow a window to be resized beyond its (custom)
screen's size. Finally, not all windows come with a sizing gadget. Overscan
is smart enough to detect all such situations, and when one occurs Overscan
does not attempt to improve the screen/window.
There is another type of programs which is so rare that it wouldn't warrant
mentioning if not for TextCraft Plus. These programs, or shall I say 'this
program', will actually crash with Overscan. Resizing TextCraft Plus's
window past a certain height (somewhere in the neighborhood of 220 lines)
causes it to go bananas. Why a program should crash when given a few more
lines for its display is completely beyond me.
For complete technical and compilation details refer to the following
files:
overscan.doc
overscan.c
overscan_lib.c
overscan.make
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