The Weekly Juan #3: Coordinate Systems in Morphic 3.0

Klaus D. Witzel klaus.witzel at
Tue Oct 31 14:02:42 UTC 2006

Hi Juan,

when it comes to the obstacles of computability and complexity over  
real-valued data, you might perhaps be interested in



On Tue, 31 Oct 2006 02:54:27 +0100, Juan Vuletich wrote:
> Hi Trygve,
> Trygve Reenskaug escribió:
>> Juan,
>> 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.
> Ok. Anyway, I'm not rewriting PluggableMorphs, at least not right now...
>> 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 )
> Well, Floats accumulate a lot less error than integers...
>> Cheers
>> --Trygve
> Cheers,
> Juan Vuletich

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