This revision fixes an annoyance in the airbrush feature implemented in D5845, where if the Rate curve went to zero momentarily while airbrushing (which often happens at the start of a stroke), the user may have to wait 1 second for airbrushing to resume. The issue is fixed by allowing paintops to update the spacing/timing information of a KisDistanceInformation in between painted dabs. This is something I tried to do in an early version of D5845, but it introduced bugs and performance issues, so it was removed. I believe I have fixed the bugs, and the performance is improved by having spacing updates occur only once every 50 ms, instead of every tablet event. These updates only happen if airbrushing is enabled, to minimize the performance impact on other brush settings.

The main change is allowing paintops to update the spacing every 50 ms when airbrushing, even if no dab is painted. The patch also removes the lower limit of 1 dab per second previously imposed on the Rate curve, as that limit existed mainly to mitigate the problem addressed by this revision.

The problem of having to wait 1 second with a Rate curve linked to pressure should no longer be present; this should be tested. Since this patch makes minor changes to the code for every KisPaintOp subclass (and KisLiquifyPaintop), it should be verified that brush engines (and the liquify tool) still behave as before when airbrushing is disabled. The patch also makes modifications to the information stored in macros by the freehand tool, so it should be verified that macros work the same as before (although there seem to be significant bugs in the macro system even without the patch). The revision author has experimented with the Rate curve, the liquify tool, the macro system, and all selectable brush engines, and they seemed to work as expected.

This patch causes no new unit test failures on the author's machine. It adds a unit test for some of the new functionality in KisDistanceInformation and related classes.