'difference' blending mode not correctly rendered on a qgis composer map item (but exports properly)

[qgib]

Author Name: Mathieu Pellerin - nIRV (Mathieu Pellerin - nIRV)
Original Redmine Issue: 7461
Affected QGIS version: master

Assignee: Nyall Dawson

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1. Open the attached QGIS project (test-blend.zip)
2. Have a look at beautiful rendering of raster heatmap (with 'difference' blend mode) over streets vector
3. Open print composer 'Composer 1'
4. Notice how the composer's map item has it all wrong, as if the raster black to white was reversed, or the layer order switched

If the user exports the composer to a PNG, the exported map is rendering properly. There's only an issue with the composer's map item preview. Also, other blend modes, like multiply, are not triggering this bug.

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• test-blend.zip (Mathieu Pellerin - nIRV)

[qgib]

Author Name: Nyall Dawson (@nyalldawson)

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• assigned_to_id was configured as Nyall Dawson
• status_id was changed from Open to In Progress

[qgib]

Author Name: Nyall Dawson (@nyalldawson)

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Fixed in changeset "e6f3b2e0086bbfc3beed57855c1ec4b024ccd35d".

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• status_id was changed from In Progress to Closed