 CONSTANT: indexed-color 3
 CONSTANT: greyscale-alpha 4
 CONSTANT: truecolor-alpha 6
+
+CONSTANT: interlace-none 0
+CONSTANT: interlace-adam7 1
 
 : <loading-png> ( -- image )
     loading-png new


: png-bytes-per-pixel ( loading-png -- n )
    dup color-type>> {
        { 2 [ scale-bit-depth 3 * ] }
        { 6 [ scale-bit-depth 4 * ] }
        [ unknown-color-type ]
    } case ; inline


    lines dup first length 0 <array> prefix
    [ n 1 - 0 <array> prepend ] map
    2 clump [
        n swap first2
        [ ]
        [ n 1 - swap nth ]
        [ [ 0 n 1 - ] dip set-nth ] tri
        png-unfilter-line
    ] map B{ } concat-as ;

ERROR: unimplemented-interlace ;

: reverse-interlace ( byte-array loading-png -- byte-array )
    {
        { interlace-none [ ] }
        { interlace-adam7 [ unimplemented-interlace ] }
        [ unimplemented-interlace ]
    } case ;

: png-image-bytes ( loading-png -- byte-array )
    [ png-bytes-per-pixel ]
    [ [ inflate-data ] [ interlace-method>> ] bi reverse-interlace ]
    [ png-group-width ] tri group reverse-png-filter ;

ERROR: unknown-component-type n ;

: png-component ( loading-png -- obj )
    bit-depth>> {
        { 8 [ ubyte-components ] }
        { 16 [ ushort-components ] }
        [ unknown-component-type ]
    } case ;

: loading-png>image ( loading-png -- image )
    [ image new ] dip {
        [ png-image-bytes >>bitmap ]
        [ [ width>> ] [ height>> ] bi 2array >>dim ]
        [ png-component >>component-type ]
    } cleave ;

: decode-greyscale ( loading-png -- image )
