On 5/6/2012 7:41 PM, Dick Hollenbeck wrote: > > >>> >>> The largest distance that wx can support is INT_MAX, since it represents >>> distance often in a wxCoord or wxSize. As a scalar, a distance is always >>> positive. On most machines which run KiCad, int is 32 bits and INT_MAX is >>> 2147483647. The most difficult distance for a virtual (world) cartesian >>> space is the hypotenuse, or diagonal measurement at a 45 degree angle. This >>> puts the most stress on the distance magnitude within the bounded virtual >>> space. So if we allow this distance to be our constraint of <= INT_MAX, this >>> constraint then propagates to the maximum distance in X and in Y that can be >>> supported on each axis. Remember that the hypotenuse of a 1x1 square is >>> sqrt( 1x1 + 1x1 ) = sqrt(2) = 1.41421356. >>> >>> hypotenuse of any square = sqrt(2) * deltaX; >>> >>> Let maximum supported hypotenuse be INT_MAX, then: >>> >>> MAX_AXIS = INT_MAX / sqrt(2) = 2147483647 / 1.41421356 = 1518500251 >>> >>> This maximum distance is imposed by wxWidgets, not by KiCad. The imposition >>> comes in the form of the data structures used in the graphics API at the >>> wxDC level. Obviously when we are not interacting with wx we can use double >>> to compute distances larger than this. For example the computation of the >>> total length of a net, can and should be done in double, since it might >>> actually be longer than a single diagonal line. >>> >>> The next choice is what to use for internal units (IU), sometimes called >>> world units. If nanometers, then the virtual space must be limited to >>> about 1.5 x 1.5 meters square. This is 1518500251 divided by 1e9 nm/meter. >>> >>> The maximum zoom factor then depends on the client window size. If we ask >>> wx to handle something outside INT_MIN to INT_MAX, there are unreported >>> problems in the non-Debug build because wxRound() goes silent. >>> >>> Let: >>> const double MAX_AXIS = 1518500251; >>> >>> Then a maximum zoom factor for a screen of 1920 pixels wide is >>> 1518500251 / 1920 = 790885. >>> >>> The largest ZOOM_FACTOR in above table is ZOOM_FACTOR( 300 ), which computes >>> out to 762000 just below 790885. > > > If we don't drop the bucket on our toes, proceed carefully, watch where we > are going, it > looks like it will hold water using a virtual world sized at 2.14 meters x > 2.14 meters. > > So far so good. > > Dick
Great work Dick! Thanks for taking the lead on this. I really appreciate it. Wayne > > > _______________________________________________ > Mailing list: https://launchpad.net/~kicad-developers > Post to : [email protected] > Unsubscribe : https://launchpad.net/~kicad-developers > More help : https://help.launchpad.net/ListHelp > _______________________________________________ Mailing list: https://launchpad.net/~kicad-developers Post to : [email protected] Unsubscribe : https://launchpad.net/~kicad-developers More help : https://help.launchpad.net/ListHelp
