[Rd] re: transparency

[Ross Ihaka]

Rather than a yes/no tranparency indicator, should we consider using
entire "unused byte" as an alpha-channel? (meaning that we specify
transparency as a value in [0,255]).  Many graphics/paint programs (e.g.
gimp) do this sort of thing.  Transparency would need to be device
dependent, but a simple yes/no transparency could be obtained by
thresholding the alpha value.  This would entail a change to way indices
into colour palettes are handled, but Peter D has pointed out that this
is currently broken anyway.

The rendering extension to the X server includes support for
transparency and this might be a place to look for how screen devices
should behave.

	Ross
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