A three.js camera for capturing a view through a static window.

WindowCamera.js

THREE.WindowCamera = function(width, height, far) {
    THREE.Camera.call(this);

    this.type = 'WindowCamera';

    this.width = width;
    this.height = height;
    this.far = far !== undefined ? far : 2000;
    this.updateProjectionMatrix();
};

THREE.WindowCamera.prototype = Object.create(THREE.Camera.prototype);
THREE.WindowCamera.prototype.constructor = THREE.WindowCamera;

THREE.WindowCamera.prototype.updateProjectionMatrix = function() {
    var xo = this.position.x;
    var yo = this.position.y;
    var zo = this.position.z !== 0 ? this.position.z : 0.1;
    var f = this.far;
    var w = this.width;
    var h = this.height;
    var cx = 4 / w;
    var cy = 4 / h;
    this.projectionMatrix.set(
        cx * zo, 0,       cx * -xo, 0,
        0,       cy * zo, cy * -yo, 0,
        0,       0,       1 / f,    -zo,
        0,       0,       -1,       zo
    );
};

THREE.WindowCamera.prototype.copy = function(source) {
    
    THREE.Camera.prototype.copy.call(this, source);
    
    this.width = source.width
    this.height = source.height;
    this.far = source.far;
    
    return this;
};

THREE.WindowCamera.prototype.toJSON = function(meta) {

    var data = THREE.Object3D.prototype.toJSON.call(this, meta);

    data.object.width = this.width
    data.object.height = this.height;
    data.object.far = this.far;
    
    return data;
};