Date   : Sun, 28 Mar 2004 00:49:05 GMT
From   : Pete Turnbull <pete@...>
Subject: Re: Aspect ratio question

On Mar 27, 23:40, Thomas Harte  wrote:
>
> Simple question - am I right in thinking that the display modes
0,1,2,4 and 5 (3 and 6 being a small amount
> shorter, of course) should produce a display approximately 1.14 times
as wide as tall? So, e.g. when my emulator
> runs at 1024x768, the largest portion of the screen I can use whilst
maintaining the correct aspect ratio is
> (approximately) 932x768 pixels?

How do you work that out?  It should be 960 x 768, but that will be
splitting pixels in modes 0 and 3.  The Beeb displays in modes 0 to 6
are all the same size (mode 3 has gaps between the character lines so
it uses less memory and has fewer addressable pixels than mode 0, but
it's exactly the same screen size) and are equivalent to 5:4 or 640 x
256 pixels in mode 0 -- a ratio of 1.25 (the pixels are exactly twice
as high as they are wide).  In all the graphics modes, the logical
addressing is based on 1280 x 1024, and all the actual pixel counts are
exact submultiples of 640 wide and 512 high.

Of course, there are side margins and top and bottom margins around the
addressable part, but the image is basically designed to fit a 5:4
display.

-- 
Peter Turnbull
<postmaster@...                 >