chickadee » leptonic » u8*3->u32

• in - PTR8: ptr to unsigned-byte
• in - LEN: int - length of data (image width * height)
• out - PTR32: ptr to unsigned-int32
• returns: number of 32bit pixels (should be equal to LEN)

(import scheme.base 
        chicken.foreign 
        chicken.number-vector
        leptonic)

(include "leptonic-types.scm")

(define-external ppx0 ppix (pix-read "input.png"))
(define data0 (pix-get-data ppx0))

(define w (pix-get-width ppx0))
(define h (pix-get-height ppx0))
(define len (* w h))

(define v8 (make-u8vector (* len 3) 0))
(u32->u8*3 data0 len (location v8))

;; ... modify v8 ...

(define-external ppx1 ppix (pix-create w h 32))
(define data1 (pix-get-data ppx1))

(u8*3->u32 (location v8) len data1)

(define fmt (get-implied-fmt "output.png"))
(pix-write "output.png" ppx1 fmt)

(pix-destroy (location ppx0))
(pix-destroy (location ppx1))

Note: if u8vector ‘v8’ is not modified, then output to data1 (in u8*3->u32), will be identical to the input data in data0. IOW “output.png” will be a copy of “input.png”. Comparing the two image files serves as a test of the procedures: if everything is working properly, the image files should be completely indistinguishable.