[mkgmap-dev] Parameterized styles and macro languages

Mon May 12 20:50:52 BST 2014

Hi Andrzej,

On Mon, May 12, 2014 at 03:15:46PM +0200, Andrzej Popowski wrote:
>Hi Colin,
>
>>Users can customise the program and styles or develop their own, but 
>>there is no mechanism to support sharing the nuances of each type of 
>>device within the distribution.
>
>I understand the problem but I don't think mkgmap code or default style 
>is a right place to solve it. We could expect more flexibility to 
>create conditional styles from mkgamp, but any hardcoded dependency on 
>Garmin hardware would be a nightmare to maintain.

Well, I think that we could solve it in the default style to some 
extent.

The default style could add one layer of abstraction by using symbolic 
names instead of numeric type codes in the actions, and the user would 
take advantage of this if needed.

The solution would be parameterized or conditional styles and something 
similar to what the C preprocessor supports with the -D and -include 
options. Something like this:

java -jar mkgmap.jar -D campsite=0x1234 ...
or
java -jar mkgmap.jar -include edge705.h ...

where edge705.h would contain stuff like

#define campsite 0x1234
(or something equivalent in a syntax that is not too different from the 
current mkgmap style language)

Myself, I am not interested in device-specific rules, but I would like 
to have some parameters that would allow unnecessary detail to be 
pruned. There could be parameters for minimum size for landuse=* or 
natural=* or building=* polygons, or the minimum length of 
highway=service to render in each resolution level. The parameters could 
also include the list of resolutions to generate.

I am not sure if the mkgmap core language should include a parameter 
substitution mechanism or a macro language. Perhaps we could leverage an 
external tool, such as http://pmp.sourceforge.net/ which
implements the m4 macro language in Java, including ant integration. The 
mkgmap distribution could include a parameterized build.xml for 
compiling a map with ant.

	Marko