Gimp batch open as layer

Question

I encountered a Problem using gimp batch mode. All I am trying to do is to open 2 png files as layers of one image and save them together as an Icon (.ico).

Problem: Gimp just opens the two images as seperate windows, not as two images in one layer.

My code looks the following:

(define (merge-to-icon filename layername endname)
(
    let* 
    (
        (image (car (gimp-file-load RUN-NONINTERACTIVE filename filename)))
        (drawable (car (gimp-image-get-active-layer image)))
        (adlayer (car (gimp-file-load-layer RUN-NONINTERACTIVE image layername)))
    )
    (gimp-image-insert-layer image adlayer 0 0)
    (set! drawable (car (gimp-image-get-active-layer image)))
    (gimp-displays-flush)
    (gimp-file-save RUN-NONINTERACTIVE image drawable endname endname)
))

Answer 1

For non-interactive mode:

(define (implode-imgs-save-ico fname-one fname-two)
    (let* (
            ; first main image
            (image (car (gimp-file-load RUN-NONINTERACTIVE fname-one fname-one)))
            ; them layer
            (drawable1 (car (gimp-image-get-active-drawable image)))
            ; open image as layer
            (drawable2 (car (gimp-file-load-layer RUN-NONINTERACTIVE image fname-two)))
        )

        ; add layer to image
        (gimp-image-insert-layer image drawable2 0 0)

        ;set layer mixing mode
        (gimp-layer-set-mode drawable2 SCREEN-MODE)

        ; may be some resize here

        ; merge layers
        (set! drawable (car (gimp-image-flatten image)))

        ; save
        (file-ico-save RUN-NONINTERACTIVE image drawable "my.ico" "my.ico")
    )
)

Then call it:

gimp --no-interface --batch='(moo "back.png" "top.png")' -b (gimp-quit 0)