The Weekly Juan #3: Coordinate Systems in Morphic 3.0
trygver at ifi.uio.no
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 http://en.wikipedia.org/wiki/Display_PostScript )
On 29.10.2006 19:16, Juan Vuletich wrote:
> Hi Folks,
> The Weekly Juan #3 is out at www.jvuletich.org . 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.
> Juan Vuletich
Trygve Reenskaug mailto: trygver at ifi.uio.no
Morgedalsvn. 5A http://heim.ifi.uio.no/~trygver
N-0378 Oslo Tel: (+47) 22 49 57 27
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