Pre-RFC, pulling rendering/labeling parameters from attributes...

[Stephen Woodbridge]

Ok, glad I read this one before posting the exact same thing! only I 
would have done my example like:

  SIZE [sizeattribute]
  ANGLE ([angleattribute] - 90.0)
  LABEL
   TEXT ("Label: " . [labelattribute] . ".")
  END

This would require a lot of changes, but could be fully backwards 
compatible.

-Steve W.

Jerry Pisk wrote:
> How about doing something similar to format strings? For example:
> 
> SIZE "{sizeattribute}"
> ANGLE "{angleattribute}"
> LABEL
>  TEXT "Label: {labelattribute}."
> END
> 
> You would need a way to disntiguish between an attribute name and an
> actual value anyway. And ity would be nice to support substitutions in
> all values when we're at it, even things like COLOR, OFFSET and so on.
> 
> Jerry Pisk
> 
> On 6/6/06, Steve Lime <Steve.Lime at dnr.state.mn.us> wrote:
>> Hi all: Before running off and doing an RFC I wanted to gather some 
>> feedback. Currently we do
>> support pulling things like angle or size from an attribute. Works 
>> fine but is clunky in many ways
>> since you see things like angleitem and angleitemindex in the 
>> structures. Adding more support
>> for will just add more needless complexity (I could see folks wanting 
>> to set colors, start angles
>> and other stuff).
>>
>> Anyway what might be nice would be to write fragments like:
>>
>>  STYLE
>>    SIZE 'sizeitem'
>>    ANGLE 'angleitem'
>>    COLOR 0 0 255
>>  END
>>
>> We could then use an hashTableObj called items to track the various 
>> values to pull from attributes.
>> At parse time the hash would contain the item names. msWhichItems 
>> could turn those into array
>> indicies (can the hashTableObj handle arbitrary types?) for speed. 
>> Then the rendering code could
>> do a quick lookup to decide whether to pull from an attribute or not.
>>
>> It would be very easy to add support for new parameters then, just 
>> tweak the high-level rendering
>> code (before handoff to native drivers). In MapScript we'd need a 
>> method to set a style or label
>> items (e.g. $style->setItem('angle', 'myAngleItem');) or just use the 
>> hashTableObj interface.
>>
>> The bad? Syntax change (I'd leave labelitem and classitem alone) so 
>> this would be a good 5.0 feature.
>> There might be a perforance hit with the high number of hash lookups.
>>
>> Worth thinking about?
>>
>> Steve
>>
>