Subject:
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Re: [LSC] Colour Definition meta-statement
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Newsgroups:
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lugnet.cad.dev
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Date:
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Fri, 23 Jan 2004 19:35:39 GMT
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Viewed:
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1791 times
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In lugnet.cad.dev, Steve Bliss wrote:
> > > ALPHA a - The alpha channel (transparency) value. a is a byte
> > > value, where 0 is totally colorless and #FF is completely opaque.
> > > LDraw programs that use dither-transparency recognize values 1-127
> > > as transparent, and 128-255 as opaque.
> >
> > I'm not sure what you mean about
> > the dither-transparency. Nobody supports this format yet, so why
> > are we concerned about special meanings for old programs?
>
> Actually, most programs use 'dither-transparency'. When I wrote
> 'dither-transparency', I meant 'rendering transparent surfaces by
> drawing with a stippled brush, specifically a brush where the
> stipples form a checkerboard pattern'. Please don't get hung up
> on my use of the term 'dither' in this context.
I realize many current ldraw rendering programs use a stipple pattern
to render transparent surfaces. I do it in ldglite because I'm too
lazy to do the sorting required to use alpha blending. However, I
don't really want the specs to dictate *how* I do it because I may change
that someday. The metacommand definition should allow me to specify an
rgb and alpha value and let the program worry about how (or when) to
convert the alpha value into a stipple pattern. I might decide to use
25%, 50%, and 75% patterns depending on which is closest to the alpha
value. I think it's best if you just strike the dither-transparency
sentence from the specs.
> > > DITHER d - Specifies the color should be dithered, and provides
> > > the second color value. d may be either a color code or an RGB
> > > value. DITHER is optional.
> >
> > Are you thinking about original LDRAW compatibility here, or about
> > future needs? I see this as a good way to represent dithered
> > printing like on the 6190 aquashark baseplate, and perhaps to provide
> > a separate color for the embedded bits in the pearly bricks, but not
> > much else.
>
> I expect most dithered printing to also be gradiated (gradiented?).
> So, IMO, a DITHER option on a color definition would only be of limited
> use to resolve the half-tone printing issue.
Maybe so, but it would certainly come in handy on the aquashark
craterplate. What about the idea of using the DITHER color to describe
the color of the embedded bits in METALLIC colors?
Perhaps if you really want to dictate how to represent an ARGB color
with a checkerboard stipple pattern you should use a tag like this:
STIPPLE 50% #AARRGGBB #AARRGGBB.
Don
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Message has 1 Reply:
 | | Re: [LSC] Colour Definition meta-statement
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| (...) OK, I'm alright with that. (...) If that's a needed parameter, I'd rather have it follow the METALLIC keyword. (...) I'm ok with that, too. Is '50%' really an adequate description? There can be many brush patterns... Steve (20 years ago, 6-Feb-04, to lugnet.cad.dev)
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Message is in Reply To:
| | Re: [LSC] Colour Definition meta-statement
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| (...) [snippety] (...) [doo-dah] (...) I was thinking no space. So far, we've avoided wrapping literals in quotes in LDraw (with only occasional trouble). I'd like to keep avoiding quotes. [snippety-ay] (...) Good question. We hadn't thought about (...) (20 years ago, 23-Jan-04, to lugnet.cad.dev)
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