PDF Transparency support in e_GDIPlus and e_BuiltIn rasterizer

Q: I've been playing with transparency in our program. Is the PDF
transparency equally supported in bother e_BuiltIn and e_GDIPlus

A: The complete support for PDF transparency is available only in the
cross-platform (i.e. 'built-in') rasterizer. Because GDI/GDI+ graphics
model is not fully compatible with PDF, it is not possible to
implement the complete support for PDF transparency using GDI/GDI+.
To be more precise, it is possible to implement such a rasterizer,
however it would eventually be reduced to 'built-in' rasterizer and
all advantages of the current GDI+ rasterizer (vector output, EMF/WMF
output, etc) would vanish.

Q: What makes transparency so difficult using GDI+?
A: GDI+ supports for transparency is limited to a constant opacity
value. In PDF the transparency model is more complex (some the
parameters that can be involved are: Source shape, Object shape, Mask
shape, Constant shape, Source opacity, Object opacity, Mask opacity,
Constant opacity, Isolated/Non-isolated group, Knockout, blending
color space, blend function, etc). For more information on PDF
transparency, please refer to Section 7 'Transparency' in the PDF
Reference (www.pdftron.com/downloads/PDFReference16.pdf).