Bug report #16396
Updated by salvatore fiandaca about 5 years ago
Combination of blending techniques can be used to produce a composer map item that achieve transparency in composer view but is exported as an opaque white object when exporting to PNG.
I produced a demonstration .qgs file embedded in the attached zip.
This is what you see in the composer.
!qgis_view.png!
This is what you get when opening the resulting png using gimp.
!gimp_view.png!
As you might notice map 3 & 4 both achieve transparency because the yellow rectangle in the background is visible in the resulting png.
However a white background is applied on map 4 for whatever reason.
Tested on windows 10 & Ubuntu 14.04 with Qgis 2.18.5
I produced a demonstration .qgs file embedded in the attached zip.
This is what you see in the composer.
!qgis_view.png!
This is what you get when opening the resulting png using gimp.
!gimp_view.png!
As you might notice map 3 & 4 both achieve transparency because the yellow rectangle in the background is visible in the resulting png.
However a white background is applied on map 4 for whatever reason.
Tested on windows 10 & Ubuntu 14.04 with Qgis 2.18.5