Bug report #13332
improperly drawn lines may occur on polygon/line features
|Affected QGIS version:||master||Regression?:||No|
|Operating System:||Easy fix?:||No|
|Pull Request or Patch supplied:||No||Resolution:|
|Crashes QGIS or corrupts data:||No||Copied to github as #:||21386|
When Settings|Options|Rendering, Rendering quality: "Make lines appear less jagged at the expense of some drawing performance" is turned OFF there is a line drawing problem for linestring and polygon features where a line is drawn across the map instead of following a series of vertices. This happens when some of the vertices are off-screen.
This occurs when the border or pen width is equivalent to less than 1 pixel -- 0.26 mm being the default. On a 96dpi display 1 pixel = 0.26458333 mm, approximately.
Changing the line width to 0.264584 (just more than 1 pixel) keeps the improperly drawn lines from appearing.
The problem occurs for both the main feature rendering and when the feature is selected. Note that the line width settings don't affect the selection rendering.
At first I thought it was related to a particular computer until I realized that another computer with the same version of QGIS was set for 192dpi so the problem showed only sometimes, as when a feature was selected. I changed the line width to 0.13 (less than 1 px) and the problem would occur on this computer as well. Also noticed that 32-bit versions didn't appear to have the problem.
On further testing, it appears that the 32-bit versions don't exhibit the problem and that 64-bit versions dating to 2.10 or earlier do have the problem.
I consider this to be a relatively minor problem, but it could lead to misinterpreted data.
Attached files showing various aspects.