[QGIS-Developer] QGIS symbology: jumping point and line pattern fills

[Martin Dobias]

Hi Andreas

On Thu, Jul 9, 2020 at 11:17 AM Andreas Neumann <a.neumann at carto.net> wrote:
>
> Working recently extensively with point and line pattern fills, I noticed that with each pan, the point and line pattern fills in QGIS kind of "jump" around relatively to their geometry, as if the offset of the pattern was kind of "random".
>
> You can see it in this video: https://www.youtube.com/watch?v=V4ytwM59_jY
>
> Is there any setting so I can avoid this behavior? Or could a QGIS dev with experience in symbology help fix this issue? I would assume if someone creates tiles from this, they would also run into issues at tile borders, because of this.

There is a checkbox to fix that in Project Properties > General tab >
General Settings section > Avoid artifacts when project is rendered as
map tiles

I think by default the patterns start at [0,0] screen coordinates,
while this checkbox will anchor patterns at some map coordinate,
making the pattern consistent at one map scale. As the checkbox label
says, there is supposedly some performance degradation, but not sure
by how much. Maybe if the impact is low, it would make sense to have
it enabled by default...?

Regards
Martin