Linking 3D rotation to opacity

[Dan Ebberts]

Give this a try:

fadeAngle = 35;

v1 = toWorldVec([0,0,1]);
try{
C = thisComp.activeCamera;
v2 = C.toWorldVec([0,0,1]);
}catch (err){
v2 = [0,0,1];
}
angle = radiansToDegrees(Math.acos(dot(v1,v2)));
ease(angle,0,fadeAngle,100,0)

Dan

[Lauren Roundy]

Thanks, but not sure exactly how to apply this. Do I just apply it to the opacity of my individual layer?

It gave me an error when I tried, said “invalid numeric result (divide by zero?)” or something.

[Dan Ebberts]

Ah, OK. Try this one (apply it to Opacity). It assumes you have a camera named “Camera 1”.

fadeAngle = 35;
v = toCompVec([0,0,1]);
d = length(toWorld(anchorPoint),thisComp.layer(“Camera 1”).toWorld([0,0,0]));
c = v[2]/d;
ease(c,Math.cos(degreesToRadians(fadeAngle)),1.0,0,100)

Dan

[Lauren Roundy]

Excellent… This worked great! Thank you so much.

A couple more questions, if you’re willing… How can I get the opacity transition to happen or ease a bit more gradually (so it’s not so harsh)? Also, how difficult would it be to apply this same idea to scale and bluriness of the fast blur effect?

I’m sure I could figure these others out with some tweaking, but I just don’t understand exactly what this expression is doing (what does toCompVec or Math.cos(degreesTRadians),1.0,0,100 mean?

Thanks!

[Dan Ebberts]

To make it less abrupt, I guess you could increase the fade angle, and/or play around with changing ease() to easeIn() or easeOut() or even linear().

Here’s a version that should work with any property, you just need to edit the first two lines:

startVal = 0;
endVal = 100;
fadeAngle = 60;

v = toCompVec([0,0,1]);
d = length(toWorld(anchorPoint),thisComp.layer(“Camera 1”).toWorld([0,0,0]));
c = v[2]/d;
ease(c,Math.cos(degreesToRadians(fadeAngle)),1.0,startVal,endVal)

For scale you would change the first two lines to something like this:

startVal = [100,100];
endVal = [150,150];

For blur, something like this:

startVal = 15;
endVal = 0;

Dan

[Lauren Roundy]

Thanks. This version helps me understand much better what to adjust and what not to.

Again, THANKS!

[Yono Yo]

Hi,

I’m trying to do quite the same thing : I created a cube and placed logos on each face of it.
The cube is rotating around its x and y axis. I want the opacity of each logos to be full when the camera faces them and to be null the rest of the time.

[Dan Ebberts]

You’re probably looking for something like this:

toCompVec([0, 0, 1])[2] > 0 ? value : 0

Dan

[Yono Yo]

Yes actually, but I’d like the logo to disapear slightly before that it does with this expression, otherwise it can be seen trought the cube, because of the perspective.

I thought replacing the 0 of your expression by 0,1 for instance would do the job :
if ( toCompVec([0,0,1])[2] > 0,1 ) 100 else 0

But that wouldn’t work…

Thanx for the quick response by the way !

[Yono Yo]

shame on me I put a “,” instead of a “.”

Anyway I don’t understand this expression : does it make a projection of the world’s z vector on the comp z vector ? So the resulting value would evolve between -1 and 1 ?