Adobe After Effects ExtendScript code

align_frame.jsx

/*
Jim Schmitz
2017.11.27
NYU-ITP 2019
http://ixora.io/itp/
    
Script for duplicating the special effects of "simulacra" in After Effects.

https://vimeo.com/123006429

My rendition is here: https://vimeo.com/244769141

Created for Gabe's Animation class.
*/

{
    function alignFrame()
    {
        var scriptName = "Align Frame";
        var BASEDIR = "D:/Projects/ITP/Animation/ITP Walk";
    
        // is a composition selected?
        var activeItem = app.project.activeItem;
        if ((activeItem == null) || !(activeItem instanceof CompItem)) {
            alert("Please select or open a composition first.", scriptName);
            return false;
        }
        var activeComp = activeItem;
        var compName = activeComp.name;

        // is there a camera?
        var cameraLayer = activeComp.activeCamera;
        if (cameraLayer == null) {
            alert("Composition has no active camera", scriptName);
        }

        // is a single layer selected?
        var selectedLayers = activeComp.selectedLayers;
        if (activeItem.selectedLayers.length != 1) {
            alert("Please select a single null layer", scriptName);
            return false;
        }

        // is that single layer a null layer?
        var nullLayer = selectedLayers[0];
        if (nullLayer == null || !nullLayer.nullLayer) {
            alert("Single layer selected must be a null layer", scriptName);   
            return false;
        }

        // import the correct image
        var frameNum = nullLayer.time / activeComp.frameDuration;
        var options = new ImportOptions();
        // looks for files in a "frames" subdirectory
        options.file = new File(BASEDIR + "/frames/" + compName + "/" + compName + "_" + pad(frameNum, 5) + ".jpg");
        var imageLayer = activeComp.layers.add(app.project.importFile(options));
        imageLayer.moveBefore(nullLayer);
 
        // gather variables
        var camera = cameraLayer.position.value;
        var orientation = cameraLayer.orientation.value;
        var r0 = nullLayer.position.value;
        var width = imageLayer.width;
        var theta = 110;

        app.beginUndoGroup(scriptName);

        // necessary prework
        imageLayer.threeDLayer = true;
        imageLayer.parent = nullLayer;
        nullLayer.orientation.setValue(orientation);
        imageLayer.orientation.setValue([0, 0, 0]);
        
        // now do the math
        var rot = new RotationMatrix(orientation);
        var xp = rot.preMult([1, 0, 0]);
        var yp = rot.preMult([0, 1, 0]);
        var zp = rot.preMult([0, 0, 1]);
        
        var a = dot(zp, r0 - camera);
        var b = (width / 2) / dtan(theta / 2);
        var r = camera + a * zp;
        
        var scale = 100 * a / b;
        var position = [dot(xp, r - r0), dot(yp, r - r0), 0]
        
        // position into place
        imageLayer.scale.setValue([scale, scale, scale]);
        imageLayer.position.setValue(position);

        // position in time
        imageLayer.inPoint = nullLayer.time;
       
        app.endUndoGroup();

        return true;
    }

    alignFrame();
}

// helper functions
function pad(num, size) {
    var s = "000000000" + num;
    return s.substr(s.length-size);
}

function deg2rad(val) {
    // convert radians to degrees
    return Math.PI * val / 180;
}

function dcos(value) {
    // cos of angle in degrees
    return Math.cos(deg2rad(value));
}

function dsin(value) {
    // sin of angle in degrees
    return Math.sin(deg2rad(value));
}

function dtan(value) {
    // tan of angle in degrees
    return Math.tan(deg2rad(value));
}

function dot(a, b) {
    // dot product
    return a[0] * b[0] + a[1] * b[1] + a[2] * b[2];
}

// Tait-Bryan XYZ rotation matrix
function RotationMatrix(orientation) {
    var c1 = dcos(orientation[0]);
    var s1 = dsin(orientation[0]);
    var c2 = dcos(orientation[1]);
    var s2 = dsin(orientation[1]);
    var c3 = dcos(orientation[2]);
    var s3 = dsin(orientation[2]);
    
    var m11 = c2 * c3;
    var m12 = -c2 * s3;
    var m13 = s2;
    var m21 = c1 * s3 + c3 * s1 * s2;
    var m22 = c1 * c3 - s1 * s2 * s3;
    var m23 = -c2 * s1;
    var m31 = s1 * s3 - c1 * c3 * s2;
    var m32 = c3 * s1 + c1 * s2 * s3;
    var m33 = c1 * c2;
    
    this.row1 = [m11, m12, m13];
    this.row2 = [m21, m22, m23];
    this.row3 = [m31, m32, m33];
    
    this.preMult = function(vec) {
        return [dot(this.row1, vec),
                dot(this.row2, vec),
                dot(this.row3, vec)];
    };
}