Question about "I" variable

[kursad]

Hi

I have started working on a shader. I can normally get what I want by creating a vector by substracting position "P" from position "eye". I also wanted to use the "I" variable described as "direction from eye to surface". But when I use it as part of a dot product I am not getting anything close to what I think I should be expecting. As you can see from the picture the upper example is wrong, and the bottom one is right.

I thought that the "I" variable was same as Renderman`s "I" variable

thanks

Edited May 24, 2010 by kursad

[anim]

why do you complement the I value?

complement is 1-X

i suppose you wanted to use Negate VOP

it'll work then

[kursad]

anim, thanks for the reply. Yeah you are right I thought the complement would work I guess Ok negate does the trick.

Thanks again

[old school]

Just to complete the thread, I is indeed the vector from the camera to the current shade point. The wrong direction to compute the dot product with the surface normal. You need to negate the I vector so that it is a new vector going from the shade point to the Eye.

Finally you need to normalize both the negated I and the surface normal or your dot product won't return a sensible value (unless that is what you want). The I vector holds the distance from the Camera to the current shade point as it's magnitude.

[kursad]

Just to complete the thread, I is indeed the vector from the camera to the current shade point. The wrong direction to compute the dot product with the surface normal. You need to negate the I vector so that it is a new vector going from the shade point to the Eye.

Finally you need to normalize both the negated I and the surface normal or your dot product won't return a sensible value (unless that is what you want). The I vector holds the distance from the Camera to the current shade point as it's magnitude.

old school, thanks for the tip, I did not know about the length aspect of that vector