[Inkscape-devel] Fixed point arithmetic in libnr causes pixel offset at large zoom

Hi all,

As reported in https://bugs.launchpad.net/inkscape/+bug/168384, bitmap pixels appear slightly offset when nearing the maximum zoom.

I found out that this is caused by the fixed point calculations in libnr, for example in nr_R8G8B8A8_P_R8G8B8A8_P_R8G8B8A8_N_TRANSFORM_0(). This is easily fixed by increasing the fixed point precision from 12 to 18 bits on line 42 in libr/nr-compose-transform.cpp, but if we do that then our headroom will become quite small. Can we switch to long long instead of just long? Or should we go to floating point math, and accept the speed penalty (if any)? Or should we leave things as they are?

Someone must have though about this before ;-)

Diederik