Adobe After Effects CS3 User Manual

Page 589

AFTER EFFECTS CS3

User Guide

584

Select the Bulge effect’s Bulge Center property in the Timeline panel and choose Animation > Add Expression, or

Alt-click (Windows) or Option-click (Mac OS) the property’s stopwatch

button.

Select the default expression text and type the following:

fromWorld(thisComp.layer("Magnifier").position)

Example: Fade a 3D layer’s opacity based on distance from camera

❖

Apply the following expression to a 3D layer’s Opacity property:

startFade = 500; // Start fade 500 pixels from camera.

endFade = 1500; // End fade 1500 pixels from camera.

try{ // Check whether there's a camera.

C = thisComp.activeCamera.toWorld([0,0,0]);

}catch(err){ // No camera, so assume 50mm.

w = thisComp.width * thisComp.pixelAspect;

z = (w/2)/Math.tan(degreesToRadians(19.799));

C = [0,0,-z];

}

P = toWorld(anchorPoint);

d = length(C,P);

linear(d,startFade,endFade,100,0)

The fade starts at a distance of 500 pixels from the camera and is complete at 1500 pixels from the camera. The

linear

interpolation method is used to map distance values to opacity values.

Example: Make a 3D layer invisible if facing away from camera

❖

Apply the following expression to a 3D layer’s Opacity property:

if (toCompVec([0, 0, 1])[2] > 0 ) value else 0

Example: Flip layer horizontally if facing away from camera

❖

Apply the following expression to a 3D layer’s Scale property:

if (toCompVec([0, 0, 1])[2] > 0 ) value else [-value[0], value[1], value[2]]