Triggering atlas preview needlessly refreshes map canvas

[qgib]

Author Name: Harrissou Santanna (@DelazJ)
Original Redmine Issue: 18691
Affected QGIS version: 3.1(master)
Redmine category:map_composer/printing

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Open a project and add a layout
Place the layout dialog so that you can view the map canvas
Check in the print layout "Generate an atlas" and choose the coverage layer
Enable the preview and press the Next button
The map canvas is refreshed in the background. I don't say that it follows the atlas feature extent; it's just rendered again. If you have labels in the map canvas or some data heavy to render, you'll see that they are cleared and then redrawn (though it's unneeded).

[qgib]

Author Name: Nyall Dawson (@nyalldawson)

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Actually this is intentional - it's so that any symbology rules which are dependent on atlas feature are correctly applied.

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• resolution was changed from to wontfix
• status_id was changed from Open to Closed