Is it possible to set the background image .. something that will:
a) Show through in alpha mode
b) Give some data to the rest of an image when the start/end row/column 
are set

Cheers!
Rick Measham

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POV-Ray doesn't have a background image specifically included in the 
SDL.  However you can create one with a bit of work:

Set a flat box sufficiently far enough away to be behind all the scene 
objects (quite far if you are using any ground planes).  Align its 
normal to be the camera normal, and compute the width based on the 
camera angle and distance from the camera.  You'll have to hit up the 
docs for info on coding that.

The image map you use should have an ambient of 1, diffuse 0 so it 
doesnt interact with the scene lights.  Don't forget no_shadow, 
no_refletion tags if you need them.

You can define some macros to update the background box automatically 
when you change the camera... but I'll let you figure out the code  ;)

I'm not sure I quite understand your other criteria...

If you use the alpha channel on your background box texture it should 
render the background color behind it, or transparent if you use alpha 
output.

By give some data... do you mean that you want the background image to 
show up for the entire render dimensions, despite having POV-Ray 
actually only render a smaller section of those dimensions?  If so, I 
don't think that's possible except by rendering in two passes and 
combining the images.   That's probably not of use to you though since 
I'd imagine you'd use that for quick test renders.

Skip

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Skip Talbot wrote:
> By give some data... do you mean that you want the background image to 
> show up for the entire render dimensions, despite having POV-Ray 
> actually only render a smaller section of those dimensions?  If so, I 
> don't think that's possible except by rendering in two passes and 
> combining the images.   That's probably not of use to you though since 
> I'd imagine you'd use that for quick test renders.

The problem is that if I set a start row, the resulting png is corrupt. 
So I figured if there was a command-line, I could set it a blank png and 
have it render the image over that.

On the other hand, I might want to just re-render a small portion of a 
picture in which case I'd use the previous full-render as the background 
and still end up with a proper png afterwards.

Now I'm probably missing something or going about things the wrong way, 
but being able to start at some arbitrary row, I feel cheated that I 
can't open the resulting file :)

Cheers!
Rick Measham

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> Now I'm probably missing something or going about things the wrong way,
> but being able to start at some arbitrary row, I feel cheated that I 
> can't open the resulting file :)


POV-Ray producing an invalid PNG after a successful render seems like a 
bug to me.  Post a minimal scene that produces the effect to 
p.bugreports, but do check to make sure it hasn't already been reported.

Skip

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Another possibility is the Environment box-method.

Let's say you create a scene in Terragen.
You then let the program render the picture for
0 - 90 - 180 - -90 and one with a pitch
towards the sky. Remember to set the camera
to 1/1 ratio.

Now you have 5 images that you can map to a
box (or cube, if you like..). When rendered
with a camera inside this cube, and if you have
been accurate, the environment will be seemless.
This can ofcourse be compared to making a
HDRI in, for instance, Terragen wich has some
advantages. But I've used the mentioned method
a couple of times with good results. Renders fast
too. :) Of course you'll have to put your lightsource
so that it matches the "sun" from the Terragen images.

Stefan

"Rick Measham" <rickm*at%isite.net.au> skrev i meddelandet 
news:434351fc@news.povray.org...
> Is it possible to set the background image .. something that will:
> a) Show through in alpha mode
> b) Give some data to the rest of an image when the start/end row/column 
> are set
>
> Cheers!
> Rick Measham

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> Is it possible to set the background image .. something that will:
> a) Show through in alpha mode
> b) Give some data to the rest of an image when the start/end row/column 
> are set

	Both are possible using the X Window display of povray-3.6.x for Unix
(see the doc/README.unix file in both PC-Linux and source distributions).
Note however that the background image won't be output to file.  For small
enough image size, this can be worked around by doing a screen capture.

	- NC

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