#SeaQuest DSV
12 messages in this thread
You can use a clip map on top of a transparency map to cast shadow
maps, since shadow maps work with clip mapping. Just remember that
the clip map is harsh edged,but the soft edges of shadow-mapping
should make up for it.
Gee…. thanks for tip. I never would have thought of that one.
Greg Teegarden – Amblin Imaging
"It's hard to believe you work in the same building as I do." <g>
Why would you want to place a clip on top of a transparency? Pretty
much defeats the purpose of raytracing through a transparency map –
you get varied transparent shadows which is not possible with a
shadow map.
John Gross – Amblin Imaging
"It's hard to believe grown-ups say this for a living."
John:
PMFJI, but I've been reading the thread, and here's my $.0002:
Here's a _really_ cool tip to get shadows with varying brightness:
Use an image processing program, and render out a B&W HALFTONE version
of the greyscale transparency map you want to use at the resolution
of your shadow map. When you use the HALFTONE as a clip map, the
fuzziness of the Shadow Mapped light will blur the halftone into a
decent greyscale. I've used this technique to cast B&W images onto a
scene. It can be used for many interesting effects (like tree shade,
etc.) (It's kind of like a slide projector, with the image as the
clip mask.)
Cool trick! a Dear John letter fer sure!
What type of dithering works best for your halftone image?
That's sounds pretty cool…
I'll have to try it.
JG
>Why would you want to place a clip on top of a transparency? Pretty much
>defeats the purpose of raytracing through a transparency map – you get
>varied transparent shadows which is not possible with a shadow map.
>John Gross – Amblin Imaging
>"It's hard to believe grown-ups say this for a living."
This trick allows you to use shadow-maps with transparency mapped
objects…that was what he was looking for… :}
>This trick allows you to use shadow-maps with transparency mapped
objects…that's what he was looking for..
But what you described isn't using a shadow map with a transparent
object, it's using a shadow map with a clip object which just happens
to be hiding a transparent object (useless to have the transparent
one then). I think he wanted to be able to cast transparent varying
shadows, but with a shadow map which is not possible…
> I think he wanted to be able to cast transparent varying shadows, but
>with a shadow map which is not possible…
It's been so darn long since the original post, I don't know WHAT he
wanted to do :} You are correct, of course, but if all he wanted was
soft-edged transparency mapped shadow maps, the clip map trick will
work, but you certainly won't get the level of results you would by
raytracing the light source through the transparency.
Grant, & John,
It has been fun watching (and helping 😉 ) this topic drift! What
"he" (me!) wanted was simply to achieve the most realistic appearance
of being underwater. I found that applying the "Essence Caustic
texture" (remember I'm using Imagine 3.0 not LightWave) directly to
objects was less convincing than it could be for three reasons. First
the texture just applies a specified color to an object. By applying
white at about 20% you can lighten the object's original color, but
NOT in the same way adding additional light would.
And second, the texture is "stuck to" the object. So while it
changes through time it also moves along with the object. In life the
changing underwater light patterns are stationary and moving
underwater objects move through them. This is a subtile one, but I'm
very picky! 😉
Finally if you are not VERY careful with the texture placement and
axis size the caustic effect will start showing up where it should
not – like on the bottom of the objects!
By applying the caustic texture (now affecting transparency rather
than color) to a "light shield" and lighting the whole scene through
it, ALL these problems are eliminated. It works wonderfully, at the
expense of having to go full trace. 🙁
This is the tip John gave me during a earlier discussion about the
SQ DSV episode about the minisub race. In that episode there were
shots that showed the sub, the bottom, AND the underside of the
surface. All lit and looking right! With this as inspiration I was
determined to create the same level of accuracy on my effect.
Although I have not yet played with color, specularity, and lighting
of the "light shield" so that it also looks like the underside of the
surface (any hints John? 😉 ) I plan to!
RE: Light shield colors
I can't remember exactly what the colors were, but they were some shade of
blue I would guess. 🙂 We also let the underside of the water surface fade
into fog colors of sky…
JG