Re: [Libosmscout-development] Multitouch zoom

[Jane J. K. <jan...@un...>]

Hi Tim,

yes, that definitely is a big help! Million thanks again! 

Was there an OSM Sommercamp? Some photos would be funny ;)

Viele Grüße
Jean

-----Ursprüngliche Nachricht-----
Von: Tim Teulings [mailto:ti...@fr...] 
Gesendet: Freitag, 12. August 2016 19:41
An: lib...@li...
Betreff: Re: [Libosmscout-development] Multitouch zoom

Hello Jane,

> I am currently implementing the pinch zoom function but I am stuck for 
> a couple of hours trying to guess how the magnification conversion 
> should be. For esthetic purposes, I need the points on which my 
> fingers touch in the beginning to remain points where my fingers are 
> at the end of the pinch action.

Right. That sounds reasonable.

> Can anybody shed some light? Which document or previous email exchange 
> explains the computation of the zoom factor with respect to the 
> variable "osmscout::Magnification magnification"?

Magnification.cpp

...
   void Magnification::SetMagnification(double magnification)
   {
     this->magnification=magnification;
     this->level=(uint32_t)log2(this->magnification);
   }

   void Magnification::SetMagnification(Mag magnification)
   {
     this->magnification=magnification;
     this->level=(uint32_t)log2(this->magnification);
   }
...

So magnification*2  <==> level+1.

With:

     enum Mag {
       magWorld     =                        1, //  0
       magContinent =                       16, //  4
       magState     =                       32, //  5
       magStateOver =                       64, //  6
       magCounty    =                      128, //  7
       magRegion    =                      256, //  8
       magProximity =                      512, //  9
       magCityOver  =                     1024, // 10
       magCity      =                   2*1024, // 11
       magSuburb    =                 2*2*1024, // 12
       magDetail    =               2*2*2*1024, // 13
       magClose     =             2*2*2*2*1024, // 14
       magCloser    =           2*2*2*2*2*1024, // 15
       magVeryClose =         2*2*2*2*2*2*1024, // 16
       magBlock     =     2*2*2*2*2*2*2*2*1024, // 18
       magStreet    =   2*2*2*2*2*2*2*2*2*1024, // 19
       magHouse     = 2*2*2*2*2*2*2*2*2*2*1024  // 20
     };


> Thank you again in advance and enjoy some time away from the computer 
> this weekend! :)

The OSM Sommercamp is definitely not "away from computer". Everybody in the room has a laptop in front of it (though most are not doing "development"). Possibly I send a photo soon...:-)

The actual projection code is in Projection.cpp as is mainly a standard Mercator projection.

Does that help?
--
Gruß...
    Tim


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