The projection matrix defines the area that is visible to the viewer. The view frustum.
203 var perspectiveMatrix = generatePerspectivematrix(150.0, 150.0, 1.0, 100.0);
This defines a view frustum with a front plane covering −150 < x < 150 and −150 < y < 150 at z = −1 and extending back to z = −100.