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Display bug with miscomputed window-start


From: Andreas Schwab
Subject: Display bug with miscomputed window-start
Date: Mon, 28 Oct 2002 17:48:49 +0100
User-agent: Gnus/5.090007 (Oort Gnus v0.07) Emacs/21.3.50 (ia64-suse-linux)

Redisplay does not correctly handle characters that wrap around at the
right margin.  To reproduce:

- Insert a bunch of ^A (C-q C-a) in a buffer so that the line wraps around
- Go to point-min
- If there is an even number of columns insert a space, so that the last
  ^A in the line wraps around, i.e the ^ is in the last column and the A
  appears at the start of the next screen line.
- Do M-1 C-v (scroll-up 1)

The cursor will now be somewhere in the middle of the window, maybe not
even inside any buffer text.  Now click on first visible ^A to move point
there and evaluate (list (point) (window-start)).  You will get two
different numbers that are off by one (`(42 41)' for an 80 column
display).

Note that if you change the character that wraps around to a TAB this bug
does not occur.

Andreas.

-- 
Andreas Schwab, SuSE Labs, address@hidden
SuSE Linux AG, Deutschherrnstr. 15-19, D-90429 N├╝rnberg
Key fingerprint = 58CA 54C7 6D53 942B 1756  01D3 44D5 214B 8276 4ED5
"And now for something completely different."




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