[patch] Workaround for scrolling problem on Intel GPU

[Yohei Endo]

Hello all,

I'm using gVim on Windows 7 32bit.
When I open a text file whose lines are of different length,
move cursor to the end of line by '$', and do wheel scroll,
then characters in the lines which are scrolled out are
sometimes left drawn.
You can see screenshots at https://github.com/vim-jp/issues/issues/715 .
It is reported that the problem occurs also on 64bit Windows (7, 8.1, 10).
I don't know whether the problem occurs also on 16bit Windows or not.

According to http://www.maruo.co.jp/turukame/3/x07939_.html (in Japanese),
The cause of this problem is assumed to be an Intel GPU bug, and can be
avoided by calling GetPixel() before ScrollWindowEx().

Attached patch is to avoid the problem.

--
Yohei Endo
yoh...@gmail.com
http://yoheie.sakura.ne.jp/

[Bram Moolenaar]

Thanks! The solution is not at all obvious.

--
"Beware of bugs in the above code; I have only proved
it correct, not tried it." -- Donald Knuth

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