Path: utzoo!mnetor!uunet!lll-winken!lll-lcc!lll-tis!ames!pasteur!agate!eris!bryce
From: bryce@eris (Bryce Nesbitt)
Newsgroups: comp.sys.amiga
Subject: Re: help: proportional gadgets
Message-ID: <7143@agate.BERKELEY.EDU>
Date: 24 Feb 88 02:10:29 GMT
References: <585@oscvax.UUCP>
Sender: usenet@agate.BERKELEY.EDU
Organization: University of California, Berkeley
Lines: 49

In article <585@oscvax.UUCP> jan@oscvax.UUCP (Jan Sven Trabandt) writes:
>
>According to the Intuition manual, in their example for a proportional
>gadget(vertical) they say...
>
>...Did things change or am I just enterpreting (sic) things wrong.

I think things changed.  Try using this:

(From the "Amiga Enhancer Manual")

Proportional Gadgets
--------------------

Consider as an example scrolling a 25 line view of a 100
line display. In the following, the variables
"visible_lines" and "total_lines" would take the values 25
and 100, respectively.

The first relationship is easy: make the Body value
represent "one-fourth." This can be expressed as

     VertBody = (ULONG)(visible_lines*0xFFFF)/total_lines;

If you can special-case zero visible_lines, then this works:

     VertBody = ((ULONG)(visible_lines<<16) -1)/total_lines;

Now, note that when you are displaying the last "page," line
75 is the top line in view (start line numbers from zero).

Therefore, when the VertPot value is a maximum (0xFFFF)  you
need to convert this to 75, and so on.  This can be done
like so:

     top_line =
    ((ULONG)(total_lines-visible_lines)*VertPot+(1<<15))>>16;

The inverse of this operation is needed if you wish to ini-
tialize the pot for some particular value of top_lines.

     VertPot = MIN(0xFFFF,
	 ((top_line_input<<16))/(total_lines-visible_lines));

The MIN macro is used because "unity" is actually 0xFFFF.

|\_/|  . ACK!, NAK!, EOT!, SOH!
{O_o} .     Bryce Nesbitt
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