[XeTeX] XeTeX, XeTeXpicfile, and transparency

Heiko Oberdiek heiko.oberdiek at googlemail.com
Fri Mar 16 19:55:31 CET 2012

On Fri, Mar 16, 2012 at 05:41:45PM +0100, Zdenek Wagner wrote:

> Image inclusion in pdftex can be achieved by pdftex primitives (if I
> remember it well, by \pdfximage etc). LaTeX packages do nothing but
> provide macros calling these primitives.

There aren't primitives for transparency. Transparency is
achieved by using low level primitives (\pdfliteral or
\pdfcolorstack* and \pdfpageresources) that define the
needed PDF constructs according to the PDF specification.
It's more complicate than applying color, because the
transparency values have to be stored in a dictionary
in the page resources. Colors don't need this.

* pdftransparent (also an example for \pdfcolorstack)
* pgf

> It is not difficult to find
> their description. the note concerning the PDF version still applies,
> transparency will be removed if the minor version is not high enough.
> The difference is that the minor version can be both queried and set
> via \pdfminorversion and most probably the default is set so that the
> transparency is supported.

Transparency was introduced in PDF 1.4.
However the TeX engines don't check whether a user/package
uses features higher than the version number would support.
pdfTeX only warns or throws an error message, if the
feature in question is in control of the engine.
Example: \pdfobjcompresslevel.

Yours sincerely
  Heiko Oberdiek

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