Re: [GD-DEVEL] [proposal] Attach DIB section buffer to gdImage

Pierre schrieb:
> I'm finishing the initial support of the new formats. The two most
> important additions for you and other users are the true 8bit per
> channel (alpha) and the contiguous buffer instead of per row
> allocation. It will let you use a DIB/BMP (or any compatible buffer)
> directly without any extra allocations or loop. It will require a lof
> tests and work to get stable enough for 2.1.x :)

For what it's worth, there is a documentation of the Windows
DIB/BMP in-memory format at the following URL:

   http://support.microsoft.com/?scid=kb%3Ben-us%3B81498&x=12&y=14

It appears that some alignment issues must be observed in order
to be able to use plain RGB-style buffers directly on Microsoft Windows:

"Every scanline is DWORD-aligned. The scanline is buffered to alignment;
the buffering is not necessarily 0." (On Windows, a DWORD equals 4 bytes.)

But things get even worse:
- "Red, green, and blue bytes are in reverse order (red swaps position
   with blue) from the Windows convention."
- "The scanlines are stored upside down"

(The article blames the latter two conventions on some alleged OS/2
Presentation Manager compatibility.)

So unless the pending (new) GD in-memory data format will offer
a possibility for "DWORD 4-byte alignment padding" upon creation of
a new image buffer, exporting a GD image to a Microsoft Windows DIB
will require copying of the whole image (in addition to the additional
RGB/BGR and upside-down hassle).

Yours,
Markus.