Raster layer opacity

[Jonathan Coles]

Am Mittwoch, den 23.03.2005, 10:41 -0500 schrieb Jonathan Coles:
> Here'a question: Is opacity a property of all layers or just raster
> layers? perhaps we can't support opacity in vectors layers just yet, but
> should that mean we shouldn't anticipate it? If opacity is a property of
> all layers then I can refactor the opacity methods in RasterLayer into
> BaseLayer.

further questions:

a) if alpha blending is not available (i.e. wxWidgets < 2.5.3) should
the renderer fall back to using a bitmask, or should it just draw the
entire image as though no masking was selected. the latter is the
current behaviour. even if the renderer falls back to a bitmask, the
selected option in the properties dialog should remain alpha.

b) should the masking information be added to the session file? now
there are three options for masking: none, bitmap, and alpha. alpha has
a level setting too.

c) this is question which addresses an HCI issue. i'll give a specific
example first, but this applies to a more general problem. i'll assume
for the sake of argument that we decide to save the masking setting in
the session file.

let's say that alpha blending is selected with opacity level 128. the
session is saved. later the method is changed to use a bitmap (for
whatever reason). the session is saved again. in the RasterLayer class,
as it stands now, the mask type and the opacity are two independent
settings. conceivably, the opacity level can stay in the session file
regardless of the mask setting. the benefit would be that if the user
decides to revert back to using alpha blending, the original opacity
level is still available. so the question here is: is this acceptable
behaviour?

to make this a more general question: should we save information about
the state of an option that has used in the past, whether it is
currently used by the active session or not, so that when/if the user
decides to return to past settings (even across multiple sessions), they
don't have to remember (or waste time recalculating) past values?

i think this can be a very powerful feature if we decide that "yes" is
the answer. although there may be some objection in that this can
increase the size and/or complexity of the session file, please remember
that our objective should be to make a product that improves the lives
of the *users* not the developers (although this is a good thing too :)

thanks,

--jonathan

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 Jonathan Coles                               http://www.jpcoles.com
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