On 06/21/2019 11:40 AM, [email protected] On Behalf Of Jon Elson 
wrote:
> The first picture looks like it is doing some kind of transliteration into 
> Cyrillic, is it possible the font selection got switched?
> Jon

Not that simple. The fonts get corrupted one by one, and character 
substitutions aren't just Cyrillic - they are numbers and punctuation also.

I can provoke it fairly easily by starting three or four standard VMS 
applications - e.g. Paint, Fileview, and Calendar, maximising them to 
full-screen and using right click to lower them to see the underlying windows.

My suspicion is that it is memory trampling in the font caching implementation 
in the emulated VCB02 device in SimH. The VCB02 device uses the same memory 
planes for font caches as for screen bitmaps - the manual says:
1.6.1.1 Font Storage and Access Fonts are stored in an undisplayed portion of 
the bitmap. Ordinarily, a font is stored only in one plane and is transmitted 
from that plane to itself and
others when a character is written.  .... Fonts are normally stored in the 
off-screen portion of the VCB02 bitmap.

Calling Matt Burke - can you spot anything odd in your implementation of this 
aspect of the VCB02?

-- 
Paul  Hardy
web: www.paulhardy.net



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