Re: DHGR Video Riddle Solved!!!

[CUTblakeney@home.com (Jeff Blakeney)]

On Thu, 7 Sep 2000 21:01:44 -0500, "Arkain" <rwking@usa.nospam.net>
wrote:

>The IIgs, as far as I know, only uses mode 2. This is not surprising since
>that's the only mode documented in the IIe technical reference manual.

It isn't surprising to me either as that is the way I've always heard
that it worked.  The IIgs added an address that software could modify
to switch between colour and monochrome modes but none of the other
models of Apple II have this feature built in.  It would have to be
added by an expansion card.

If these modes can't be reproduced on a 128k IIe, a IIc, a IIc+ or a
IIgs, then they are not Apple II modes and therefore must be the
result of special hardware.

The Laser 128s have two modes that don't exist on any Apple IIs.
280x384 and 560x384 but I wouldn't call either of them Apple II
display modes even if there is some software that will take advantage
of the special hardware it is being run on.

>Like I said before: The color burst signal is never turned off in DHGR
>mode... at least not on a composite monitor. This leaves the screen with 560
>color-bleeding horizontal dots. Depending on the position of the dot, it
>seems you'll still get some subset of the 14 colors, but in a dot that's 1/4
>the size of the normal DHGR pixel. This means that it will normally appear
>that the screen is still in full color mode when it's not.

In 140x192 mode, each pixel is made up of a pattern of 4 pixels.  The
display hardware simply takes these patterns of pixels and displays
them as colours.  For example, using a 0 to mean the pixel is turned
off and 1 to mean the pixel is turned on, 1111 gives you a white 140
mode pixel, 0000 gives you a black 140 mode pixel and 0101 gives you a
grey 140 mode pixel.

The 140x192 mode is a logical mode.  It is used to make dealing with
colour easier.  However, the bit pattern of a 140 mode pixel adjacent
to another 140 mode pixel can affect the resulting colours that get
displayed in those two 140 mode pixels due to the way the colours are
produced so this mode isn't really the best way to think about the
display either.

>The easiest way to tell the difference is to populate the screen with 80
>column bit-mapped text. Each block, 1 byte wide & 8 rows tall, should be
>used to make a character. In mode 1 you'll be able to read whatever text you
>put on the screen, but you won't be able to predict the colors using the
>mode 2 method. In mode 2, the text will be harder to read, but the colors
>will be just what you expected.

When I get a chance I will do more testing but I really don't think I
will get any different results than I am currently getting.

>As for mode 3, the proof of it is in the fact that games like Test Drive
>display text clearly on a IIe, but blur the text with extra color blocks on
>a IIgs. If the mode were strictly mode 2, then the text would always show
>with color on the edges.

I'd have to check that out but I think my Test Drive disk died on me
ages ago (I think my little brother killed it).  However, I still see
no way for graphic text to be displayed without colouring fringing
without special hardware (something other that the Extended 80 Column
Card) or by having the characters designed and placed in such a way
that no colour fringing will occur.

+------------------------------------------------------------------------+
| Jeff Blakeney - Dean of the Apple II University in A2Pro on Delphi     |
|                    Delphi Apple II Forums Web Pages                    |
| A2: http://www.delphi.com/apple2   A2Pro: http://www.delphi.com/a2pro  |
+------------------------------------------------------------------------+