Too many canvas refreshes imacts feature editing

[qgib]

Author Name: Alexey T (@Xeenych)
Original Redmine Issue: 21472
Affected QGIS version: 3.6.0
Redmine category:map_tools

---

I have a heavy project. Redrawing it takes near a second or a two.

Canvas refresh happens every time when

1. selecting a feature
2. deselecting a feature
3. Toggling editing mode
4. moving feature, or feature vertex

It is impossible to edit something in this case.

QGIS 2.18 doesn't behave like this.

The video, showing the difference in 2.18 and 3.6 is here
https://yadi.sk/d/oGakaJc77ilkNQ

[qgib]

Author Name: Nyall Dawson (@nyalldawson)

---

Please check the label settings for the layer being edited in both versions - I suspect the difference is due to different label settings in the 3.x project causing a complete redraw.

---

• status_id was changed from Open to Feedback

[qgib]

Author Name: Alexey T (@Xeenych)

---

First, QGIS redraws all layers, not only the layer being edited.
Second, the projects and label settings are identical.

[qgib]

Author Name: Nyall Dawson (@nyalldawson)

---

I cannot reproduce. There is a specific setting in your project which is causing this to happen, or possibly it's due to an installed plugin changing the behaviour.

[qgib]

Author Name: Alexey T (@Xeenych)

---

No and no. No plugins. Just a very large project. Once again a have to explain this as in #22189. Download sample dem data from that issue and test.

[qgib]

Author Name: Alexey T (@Xeenych)

---

Test this roject please.
https://yadi.sk/d/YeIFSsxmVghSQg

Select "line" layer. Then use vertex tool to edit a feature.
QGIS 3 will refresh canvas after each change. As this is slow, it is impossible to edit features comfortably.
QGIS 2.18 will refresh canvas only if really needed.

[qgib]

Author Name: Giovanni Manghi (@gioman)

---

Alexey T wrote:

Test this roject please.
https://yadi.sk/d/YeIFSsxmVghSQg

Select "line" layer. Then use vertex tool to edit a feature.
QGIS 3 will refresh canvas after each change. As this is slow, it is impossible to edit features comfortably.
QGIS 2.18 will refresh canvas only if really needed.

just tested your project on 3.6, select the "line" layer, toggled editing and made some node/segment changes and/or selection. No refreshes.

[qgib]

Author Name: Giovanni Manghi (@gioman)

---

• category_id was changed from GUI to Map Tools

[qgib]

Author Name: Alexey T (@Xeenych)

---

Strange. Cannot reproduce it too now. May be I've changed some QGIS settings. Will investigane

[qgib]

Author Name: Giovanni Manghi (@gioman)

---

Ask to reopen if you find a/the real problem.

---

• status_id was changed from Feedback to Closed
• resolution was changed from to invalid

[qgib]

Author Name: Alexey T (@Xeenych)

---

I think this should be reopened.

"Use render caching if possible to speed up redraws" should be enabled in QGIS render settings.

Check this video please.
https://yadi.sk/d/NOzf9wBovWelHg

Add a label to "line" layer. Add label to dem layer. Labels may be empty
Then, editing "line" layer couses full canvas redraw, which is slow.

[qgib]

Author Name: Giovanni Manghi (@gioman)

---

Alexey T wrote:

I think this should be reopened.

"Use render caching if possible to speed up redraws" should be enabled in QGIS render settings.

Check this video please.
https://yadi.sk/d/NOzf9wBovWelHg

Add a label to "line" layer. Add label to dem layer. Labels may be empty
Then, editing "line" layer couses full canvas redraw, which is slow.

with labels on (even empty) I see a redraw, also on 2.18 and regardless of the "Use render caching if possible to speed up redraws". This is also your observation? if yes I guess that this is how it works (not sure 100%) so this should be possible be filed as a feature request/improvement (but I have a vague idea that I filed a similar ticket many years ago and the answer was that it wasn't possible to improve much this area when labels are on... but again my memory could fail me).

[qgib]

Author Name: Alexey T (@Xeenych)

---

As labels are always drawn on top of all rasters and vectors, I think QGIS might redraw labels only, when editing features, leaving already rendered vectors and rasters intact.
May be label reposition somehow breaks caching?

[qgib]

Author Name: Giovanni Manghi (@gioman)

---

Alexey T wrote:

As labels are always drawn on top of all rasters and vectors, I think QGIS might redraw labels only, when editing features, leaving already rendered vectors and rasters intact.
May be label reposition somehow breaks caching?

I'll leave the answer to a core developer.

[qgib]

Author Name: Alexey T (@Xeenych)

---

Shouldn't this bug be reopened?

[qgib]

Author Name: Giovanni Manghi (@gioman)

---

Alexey T wrote:

Shouldn't this bug be reopened?

#18853