Clarification using _MEM

[TerryRitchie]

Ok, thank for the replies guys, that does make sense. I wrote a subroutine the makes a negative image (inspired by another recent post) and wanted to see how small and fast I could make it. Here is what I have:

Code: (Select All)

' _______________________________________________________________________________________________________
'/                                                                                                       \
SUB __Negative (i AS LONG) '                                                                  __Negative |
    ' ___________________________________________________________________________________________________|___
    '/                                                                                                       \
    '| Creates a negative image                                                                              |
    '|                                                                                                       |
    '| i - the image to work with                                                                            |
    '\_______________________________________________________________________________________________________/

    DIM MemBlock AS _MEM '           memory block holding image data
    DIM Offset AS _OFFSET '          pixel location within memory block
    DIM Pixel AS _UNSIGNED LONG '    pixel data at pixel location
    DIM Size AS LONG '               total number of pixels

    Size = _WIDTH(i) * _HEIGHT(i) '       calculate number of total pixels
    MemBlock = _MEMIMAGE(i) '             set memory block to image data
    Offset = MemBlock.OFFSET '            get start position of memory block
    $CHECKING:OFF
    DO '                                  begin pixel count
        _MEMGET MemBlock, Offset, Pixel ' get pixel data from memory block
        Pixel = 16777215 XOR Pixel '      make negative (only RGB is affected, not alpha)
        _MEMPUT MemBlock, Offset, Pixel ' update pixel color in memory block
        Offset = Offset + 4 '             next pixel location in buffer
        Size = Size - 1 '                 decrement pixels remaining
    LOOP UNTIL Size = 0 '                 leave when no pixels remain
    _MEMFREE MemBlock '                   free memory block
    $CHECKING:ON

END SUB

As you can see I use a variable named Size that calculates the total number of pixels and then use that as a count down within the loop. I thought I could use .SIZE to achieve this same result and remove another variable from my subroutine.