Decodes a XCF image to a mapping, with at least an
'image' and possibly an 'alpha' object. Data is either a XCF image, or
a XCF.GimpImage object structure (as received from __decode)
Supported options
([
"background":({r,g,b})||Image.Color object
"draw_all_layers":1,
Draw invisible layers as well
"draw_guides":1,
Draw the guides
"draw_selection":1,
Mark the selection using an overlay
"ignore_unknown_layer_modes":1
Do not asume 'Normal' for unknown layer modes.
"mark_layers":1,
Draw an outline around all (drawn) layers
"mark_layer_names":Image.Font object,
Write the name of all layers using the font object,
"mark_active_layer":1,
Draw an outline around the active layer
])