To:	ma6djh AT bath DOT ac DOT uk
Cc:	djgpp AT delorie DOT com
Subject:	Re: Style AND speed in C++? How? Please, I need some radical
	ideas on this one!
Message-ID:	<19970430.204530.7119.0.fwec@juno.com>
References:	<c=GB%a=_%p=Indigo_Active_Vi%l=CRIANLARICH-970421130655Z-367 AT crianlarich DOT indigo>
From:	fwec AT juno DOT com (Mark T Logan)
Date:	Wed, 30 Apr 1997 20:46:36 EDT

On Sat, 26 Apr 1997 18:28:20 GMT ma6djh AT bath DOT ac DOT uk (D J Hampson) writes:
>> I'm pretty sure that the overhead of a virtual function call could
cause 
>> you some problems.  It's OK to use virtual function for setup or 
>> something but don't use it for putpixel or linedraw.

>The way I was going to do it was to have a screen mode class for
whatever 
>mode I'm in (just 320x200x256 to start with), with three private buffers

>(for triple-buffering), but a public reference to the current buffer to 
>draw in. So it's just as quick as the best C equivalent for putpixel and

>getpixel, and I can write seperately whatever line drawing routine I 
>want, but I can switch modes (VESA or whatever when I find out how it
all 
>works!) completely independantly of the rest.

that is part of what c++ is about, being able to switch modes, and keep
that code
*totally* independent of the rest of the program.  However, C++ is also
about protecting
your data members.  If you wish to program with true C++ class (pun
intended), you
cannot have any public data members.  (Question for the gurus: Is there
any situation
where this is not the case?).  The reason for this is that when you have
a class, the only
thing that can touch the variables inside the class are the class's
member funtions.  This
is advantageous (did I spell that right?) because when a variable somehow
comes to
have a bogus value inside of it, you know for a fact the class itself is
at fault.  Now you know
where to begin debugging.  And knowing is half the battle :-)


>The screen mode class will do all the stuff like set up the screen 
>interrupt code and find the most recently draw screen to chuck on 
>0xa0000.

If you want to make the code portable, you should isolate the hardware
specific stuff from the
program code.  In other words, have a screen class, but have the class
call functions for setting
the screen mode.  These functions contain *all* of the hardware specific
stuff, and are in their
own seperate file(s).  Then when you want to port the program, you have a
couple of isolated
files to rewrite, instead of a whole program.

Good luck,


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