The Weekly Juan #3: Coordinate Systems in Morphic 3.0

Trygve Reenskaug trygver at
Mon Oct 30 10:18:32 UTC 2006

Many thanks for your open discussion. Hans-Martin has given well-founded 
comments. There is a lot of solid experience in them that I recognize 
and that should be useful in your work.

I would like to add two comments based on my own experience.

1) I underestimated the geometric complexity of even a simple window - 
until I drew ALL the relevant rectangles in a scrollable text editor. (I 
believe I have the report somewhere, but can't find it). There were the 
outer view rectangles outside and inside the border. Then the scrollbar 
with all its details. The text viewport outside and inside the border, 
and the text view itself. The problem was that every rectangle was 
handled and even named somewhere in the code. Hap-hazard naming lead to 
an abundance of synonyms and homonyms which made it hard to find and fix 
the many bugs. Much grief would have been avoided if naming had been 
taken seriously from the very start. The complexity of the ST80 code is 
partly caused by naming problems but mainly, I believe, by complexity 
inherent in the task.

2) An off-by-one error is very visible on the screen and very 
irritating. We once used floats for certain coordinates. Accumulating 
errors caused problems even after we changed to double precision floats. 
On the other hand, I believe Display PostScript  (and PS itself) uses 
float coordinates? If so, it could be worth while to look into how users 
of DPS protect against cumulating errors.
(See )


On 29.10.2006 19:16, Juan Vuletich wrote:
> Hi Folks,
> The Weekly Juan #3 is out at . Today I talk about 
> Coordinate Systems in Morphic 3.0.
> Hope you like it. Any comment is welcome, especially discussion about 
> the ideas and the design.
> Cheers,
> Juan Vuletich


Trygve Reenskaug      mailto: trygver at
Morgedalsvn. 5A
N-0378 Oslo           Tel: (+47) 22 49 57 27

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