function blur2d(horizontalExpr, verticalExpr, reps, taps, samplerNum) {
    return new Blur2dLoop(expr_1.wrapInValue(horizontalExpr), expr_1.wrapInValue(verticalExpr), reps, taps, samplerNum);
}
creates a loop that runs a horizontal, then vertical gaussian blur (anything
more than 1 pixel in the horizontal or vertical direction will create a
ghosting effect, which is usually not desirable)
@param horizontalExpr float for the horizontal blur (1 pixel default)
@param verticalExpr float for the vertical blur (1 pixel default)
@param reps how many passes (defaults to 2)
@param taps how many taps (defaults to 5)
@param samplerNum change if you want to sample from a different channel and
the outer loop has a different target