Chmod +rw P

[Wolfwood]

Howdi, here is a little question for you all,

The vex html help says,

* Although P is modifiable in the surface context, at the current time, changing P will not affect the render of the surface, only shading.

But when I try to write to P vcc throws the following error,

"test.vfl" line 4 ERROR (1031) Illegal attempt to modify read only variable "P"

P = P * 2;

        ^

REMARK (3003) 1 error and 0 warnings encountered

REMARK (3007) No output is generated due to errors in the source code

Here is a stupid sample that causes the above error,

surface
test() {
vector Nn;

P = P * 2;
Nn = normalize(computenormal(P));

Cf = diffuse(Nn);
}

Are the help files outdated and P is no longer modifiable? Or am I misunderstanding the vec docs and need more Red Bull?

jim.

[TheUsualAlex]

Hi Jim,

I am not sure if I understand you correctly, but I think that P *= 2 is not allowed as you were trying to write to "P". But I am scratching my head as to what the VEX html meant....

Can you try something like this?

surface
test() {
vector Nn;
vector newP = P * 2;

Nn = normalize(computenormal(newP));

Cf = diffuse(Nn);
}

Mo Red Bull?

ALex

[Wolfwood]

Hey alex,

I can understand not being able to write to P. Thats what displacement shaders are for.

Like you suggested I'm just using another variable. I was just wondering why the docs said it was writable.

Thanks

jim.