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Alpha Channel Problem

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Juan CarrerasAlpha Channel Problem
by on Feb 28, 2013 at 3:02:41 am

I'm trying to have a mask animated on top of a map so that gradually reveals itself:

What I have is an ocean plane with a basic water shader and on top I have a second shader with a map of the wake trail along which the ship will move. The map is fixed as in real life since the foam doesn't move but instead is left behind as the ship advances.

Then I want to have a third shader with its mapping coordinates animated along with the ship and acting as a mask will reveal the wake as the ship moves and hide the rest of it so whatever is white will be opaque showing the wake and the black will be transparent and show the ocean water.

However, the transparent areas keep coming up black. I tried all sorts of combinations with the texture tag and I'm not having any luck. I wonder whether it's even possible.

I can do it if it's all in one shader having a layered alpha (see example) but I need to be able to move one of the alphas coordinates so it needs to be a separate shader.
Attached is a scene with the two options. It needs to look like the above example but animated like the one below.

5546_sea.zip

I hope that someone can figure out what am I doing wrong ...

Thanks in advance


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Brian JonesRe: Alpha Channel Problem
by on Feb 28, 2013 at 4:22:02 am

no time to look at the moment but perhaps this could be a different way to go http://biovisioning.com/C4D_Stuff/C4D_Links.html check out the water stuff on that page, it's _old_ but it still works. There are other ways as well.


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Juan CarrerasRe: Alpha Channel Problem
by on Feb 28, 2013 at 5:47:54 am

Hi Brian,

I'm quite familiar with Jeremy's experiments. It's not quite what I'm after for this particular scene.
Thanks anyway.


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Juan CarrerasRe: Alpha Channel Problem
by on Feb 28, 2013 at 3:41:03 pm

Still no joy. Keeps giving me black instead of transparent.
I reposted the file as I noticed a mislabeled textured that couldn't be found.

5547_sea2.zip


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Brian JonesRe: Alpha Channel Problem
by on Feb 28, 2013 at 5:31:23 pm

the separate alphas - it's black because the top texture is black, it has an alpha that shows the wake but the rest is black. You could color it the same as the sea (instead of black) but then you'd have to match the mapping (right now the sea is UVW and the wake is Flat). It's easier to add an invisible object to use in a Proximal channel in the wake material itself.

5548_seawakeproximal.c4d.zip


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Juan CarrerasRe: Alpha Channel Problem
by on Feb 28, 2013 at 6:58:42 pm

Smart way however, the whole point of putting a separate alpha-only shader on top is the fact that I need to animate its mapping coordinates either with the coords or with the U offset because like I said before, the wake pattern it's not supposed to move, only the area revealed by the alpha visible area does along with the ship.

Right now your solution does essentially the same than the "layered alphas" option and the wake is solid moving with the ship.
See test renders of your solution (wake1) and an example of what I'm looking for (wake2).
Still no joy. Thanks anyway.
http://reels.creativecow.net/film/wake1
http://reels.creativecow.net/film/wake2


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Brian JonesRe: Alpha Channel Problem
by on Feb 28, 2013 at 7:52:06 pm

that's not what I get when I render it - http://reels.creativecow.net/film/testrender


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Juan CarrerasRe: Alpha Channel Problem
by on Feb 28, 2013 at 8:51:38 pm

Hi again Brian,

You are right ! my mistake, it renders how it should .... not sure what I did (I have too many tests and versions ...)
I tested it also in rough seas and I gess up to certain wave height within the proximal range it still works. Great !!
One question though that applies to this system and also my new procedural system from the previous message)

Right now both methods use a flat projection in plan view for the uv coordinates.
Is there a way to taper the mapping coordinates grid ? It would be nice to have the wake spread at the tail with the distance as in real life. Right now it's to straight and there is no change in the z direction.
If not how else could I achieve this?

tapered-projection.jpg


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Brian JonesRe: Alpha Channel Problem
by on Feb 28, 2013 at 10:07:30 pm

to scale just the back end of the texture? Not that I know of,


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Brian JonesRe: Alpha Channel Problem
by on Feb 28, 2013 at 10:08:10 pm

I'll upload another test in a bit


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Brian JonesRe: Alpha Channel Problem
by on Mar 1, 2013 at 1:34:51 am

more proximal stuff (because it can control the shape) - 5552_waketrial.c4d.zip


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Juan CarrerasRe: Alpha Channel Problem
by on Mar 1, 2013 at 4:59:00 pm

Thanks again Brian.
I managed to taper the coordinates by applying a taper in 'within box' mode behind the ship to the extents of the proximal plane you added. Then I used 'generate coordinates' to convert the flat coordinates to UV so now the taper actually deforms the map along with the mesh. Then I added a parent constraint to the taper to be dragged along with the ship. Done.

Thanks for all your tips and tests.


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Juan CarrerasRe: Alpha Channel Problem
by on Feb 28, 2013 at 8:10:48 pm

Hi again,

Actually I might have found a better solution with a layered procedural shader playing with luminance, noise and gradients. See attached. I think it's simpler and adapts to the sea waves as it's projected as flat from plan view. However, I would like it to have a tapered shape as it looks too straight and in reality the wake spreads gradually at its tail with the distance.
Is there a way to taper the rectangular grid of the flat projection map coordinates when in texture mode? See attached




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Juan CarrerasRe: Alpha Channel Problem
by on Feb 28, 2013 at 8:54:37 pm

Brian,

I added a response before the previous post (sorry, I replied out of order)


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