camera position into OSL script


(geoCrackers) #1

I need to get the camera position into my OSL shader, and I’m wondering how to do this. I know I can get the vector from the camera to a sample point, but that won’t help me. I need the vector from the camera to the origin.

In short, I need to get the camera position as a vector, take the cross-product (I think), do a small quaternion rotation around that cross product, then render the second viewpoint and mix it with the first. This isn’t supposed to be a stereo view per se, but is for verifying that stereo vision won’t interfere with some imagery - which is also generated in OSL. So I’m doing all this in OSL for real-time viewing.

Because it has to be basically real-time interactive, I’m using OSL in Cycles so we can just rotate the perspective view around - so setting up a stereo camera rig and then rendering won’t help me. I need it more interactive than that.

Though I started programming in Python before recently venturing into C (specifically for OSL), I’m not having much luck with Blender Python. My thought is that a Blender Python script could read the camera position, then create a node expressing that position as a vector. Then I would just plug that node into my shader node. Does this seem like the right approach?

thanks


(Secrop) #2

You can only calculate the camera position when the ray type is ‘camera’, multiplying the RayLength by I and adding P.

point CamPos;
float L;
if (raytype("camera"))
{
getattribute("path:ray_length", L);
CamPos=L*I+P;
}

All the other rays won’t work.

PS:Or you can get the camera position with drivers and input the vector into your shader.


(geoCrackers) #3

Thanks Secrop, I really appreciate the help. I’d been having trouble getting my OSL shader to compile, so I switched to using the trace:hitdist attribute. I’m using the osl-languagespec.pdf from github, but maybe I should be using Blender-specific docs to their implementation. Here’s what I have so far.


shader GetCam(
    point surfP = P,
    vector Inc = I,
    output point CamPos = point(0, 0, 0)
)
{
    float L;
    if (raytype("camera")) {
        getattribute("trace:hitdist", L);
        CamPos = L*I + P;
    }
}

In order to really set up my right eye view correctly, I figure I’ll need to create a copy of the camera vector with the Z value at zero, then take the cross product between those. That gives me a vector along the XY plane. Then taking the cross product of that with the camera position, I should get the “Up” vector for the camera. Then I’ll do a small quaternion rotation about that vector, and it’ll give me the right eye position.

But I just found out that they really want to view this in stereo, so I’ll need to figure out a whole lot more tricks to get these two views rendered simultaneously in separate Blender windows.

=or= instead of doing all this interactively, I could just create a camera stereo rig and path, and pre-render stuff. I was given a sprint deadline of two weeks to get a lot of stuff done for this project. :slight_smile:

-as I said, thanks very much for your help; I’m learning C on the fly as I do this stuff (migrating from Python)


(Secrop) #4

have you tried the new stereo3d/multi-view functionality (from above 2.75)?
It may be just what you need…


(geoCrackers) #5

I’ve tried the stereo side-by-side view, and it works excellently in all the viewport shading modes which I’ve tried - except for Rendered. I get a nice 3D view in all the other modes.

I still get a side-by-side view when in Cycles Rendered mode, but both views are from the same camera viewpoint. (I should mention that I’m running 2.76 on Windows 7-64).

Have I encountered a bug, or is it possible that I just have a wrong setting somewhere?


(Secrop) #6

in my monitor multi-view works, but I don’t have the possibility of testing other outputs…
maybe you could PM @dfelinto and ask him how it really works…


(tamerlan311) #7

Try this way:

point CamPos = point(“camera”, 0, 0, 0);