QGIS » QGIS Application

Patch to fix #2166, #1449, #2302
related: #2038 about render caching disabling incremental drawing - I recommend WON'T FIX on this one; reason given below and in the ticket.

I am submitting fixes for several tickets as a single patch because I worked on them pretty much together as the problems seemed to be related.

I think the patch also fixes #4174, but I was not able to reproduce the reported problem, so I am not sure what effect there is.

• render caching
• on-the-fly reprojection
• the 'Number of features to draw before updating the display' setting (incremental rendering)
• window resizing - overview or main map

None of the problems was particularly difficult to fix; what was hard was determining the exact situations that show the problems, then testing the fixes.

• don't draw (redraw) overview if already drawing - this fixes the main complaint on #2166
• don't remember last extent if not caching (see #2302). The last extent is used only for caching purposes.
• don't use the render cache for the overview - fixes 2 related issues, wrong cached image on overview or main map depending on which was last drawn, when making a layer visible - see #2302
  Redrawing the overview isn't done nearly as often as main map, except on resizing, perhaps, so shouldn't be much of a performance issue.
• set full extent for overview when resizing - see #1449 - complaint about overview (and main map) scale change on resize smaller
• Disable incremental rendering if render caching is on by ignoring the setting. Incremental rendering makes no sense if Render caching is enabled (it actually does so, but to the cache image)
  Disable the option in Settings, Options to make it obvious to user when Render caching is on.
  Documentation should note this.
• fix overview map for left mouse button press only (overlooked on a previous improvement I did) to be consistent with release and move events

Note that the windowing system event handling may cause missed repaints (incomplete repaint of window) especially if a redraw takes a significant amount of time - this is true when both main map and overview are being drawn on resizing.
In testing I have found that resizing/repainting works fairly well for overview as long as Render is disabled. If Render is on, there is often no redraw of the overview or other parts of window, like dock widget title bars.
In particular, maximizing/restoring the main window will likely not redraw the overview and the main map draws after a long pause. This problem existed before the current changes.
This is the case even without these changes.

The only thing I can offer is that a manually forced redraw be done - for the overview, toggling a layer off, then on (either way actually). And, if necessary, refresh the map.

I have tested on Microsoft Windows, but not other platforms.

• if there is a rubberband or highlight object, rendering of the map is very slow - how slow depends on the complexity of the rubberband/highlight object (number of vertices) as the object is rendered each time the display is updated during layer rendering

The situation really improved:

the overview extent still goes wild when changing the vector symbology, but now resizing the overview window "fixes" the problem. Usually when resizing the overview windows the canvas is not drawn, forcing to click the "refresh" button, but it happens also if "render caching" is not enabled.

At least now the overview seems usable.

I don't know if this improvement is because a part of the attached patch was used.

Was the attached patch reviewd/commited? if no, why?

This issue seems gobe in qgis master. Please reopen if necessary.