Protocol Changes (was: Zoom / Scaling in VNC)

[cjsmith@btinternet.com]

Hi,

As I've mentioned previously, I'm implementing a server-side scaling capability
as an extension to VNC to support low-bandwidth, low-resolution connections
(primarily for mobile, handheld PCs).

I've now modified the Win32 server to support this, using two additional protocol
messages: rfbSetScaleFactor (client requests server to change scale), and rfbReSizeFrameBuffer
(server tells client that the desktop or framebuffer dimensions have changed,
soon to allow desktop resolution to change on-the-fly without breaking VNC clients).


The question I have now is how to add these to the public protocol - we don't
want to force all servers to implement this, so increasing the protocol version
number isn't ideal. I was thinking of changing the "pad2" field of the rfbPixelFormat
into a "display features" bit-mask, so that bit 0 would indicate that the current
server and desktop settings support the scaling functions.

Is it guaranteed that *all* VNC servers will set the "pad2" field to ZERO? Does
anyone have a better idea on how to implement this protocol change?


Thanks,

Chris.

(PS - A new connection will always default to scale factor 1, so that an old
client can connect to a scaling server without any changes).

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