function dof(depth, rad, depthInfo, reps) {
    return new DoFLoop(expr_1.wrapInValue(depth), expr_1.wrapInValue(rad), expr_1.wrapInValue(depthInfo), reps);
}
creates depth of field expression; all values are mutable by default
@param depth float for what inverse depth to focus on (1 on top of the
camera; 0 is infinity)
@param rad float for how deep the band of in-focus geometry is (a value
between 0.01 and 0.1 is reasonable)
@param depthInfo float the expression that represents the inverse depth
(defaults to sampling the red component from channel 0)
@param reps how many times to repeat the gaussian blur