first I try to write down the configuration of my pi:
Pi 2B, Image from pi´s Website (Jessie may 2016) with updated kernel and System (rpi-update and abt-get update and upgrade), experimental graphic driver from pi.
glxgears shows up to 250 fps depending of the window I use.
glxinfo shows direct Rendering yes and vc4 as Driver
Running oc with the respositories packs as described on the oc webside. Not built from source.
I´m using rastercharts (made from scans from the papercharts) in the *.kap Format.
have 5 up to 50 mb depending if it is a small Detail Chart or a bigger overview Chart. When I made the charts I put two DIN A3 scans together to one DIN A2 Picture and then made a *.kap Chart.
Video mem is 256 or 128 mb (have no visuable effect).
Limited the charts with ncachelimit=5
When running oc without the gl-option everthing is ok. Panning and zooming is not very fast but ok and usable for me.
Now ´played around with the OpenGL-Option.
When using the gl-option panning und zooming is much faster.
As Bram described when zooming out too much (x1,6 and lower) then oc stops and after a couple of seconds it run down.
Using only one of my 50mb charts have the same effect.
Using only one of my small Detail charts with 5-6mb then I can zoom out without any problems. Since yet I don´t find out the Limit of mbs.
Switching quilting or the Change scale Options on or off have no effect.
Changing the ncachelimit value have no effect
It seems to be that this effect depends of the biggernes of the Chart.