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Message: 5904

Author: john_elliott_uk

Date: 20/08/2006

Subject: Re: A technical question about J. G. Harston's patch - items problem

 

In manicminerandjetsetwilly@yahoogroups.com, Daniel wrote:

So I guess - thinking aloud - that after applying the patch, the
addresses &A4xx would have to be modified manually (in JSWED's Hex
editor, I guess). But what needs to be done exactly?

As I understand the way the patch works, you need to reset bit 6 on
all items in rooms 0-63, and set it on items in rooms 64-127. Hex
values #00-#3F and #80-#BF have bit 6 reset, and values #40-#7F and
#C0-#FF have it set.

Also, why are the items invisible (in the emulator) in case of some
TAP files (after applying the patch), but they are visible and
in the wrong places in case of other TAP files?

I suspect that items being invisible is due to bit 6 being set, so
that instead of the items appearing in room , they appear in room
. Not sure why their locations would be wrong.

Does the value of the
addresses &A6xx need to be corrected as well? If so, how exactly?

It shouldn't need to be, because just before the title screen is
drawn (the code is at #8800) the item-collected flags get set for all
items. If you patch a running snapshot this may get missed, but
cold-starting from .TAP or from JSWED's Playtest option will ensure it
gets called.

It's interesting to note that JSW128 and JSW64 took the opposite
approach to expanding the item table - the 'item collected' flag and
the top bit of the item Y-coordinate stay in the #A400-#A4FF range,
and the item location moves to a new table at #C000-#C0FF.

 

 

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