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From: pete@iris49.UUCP (Pete Ware)
Newsgroups: comp.windows.x
Subject: Re: BadLength for XDrawLines
Message-ID: <9102182000.AA09355@iris49.biosym.com>
Date: 18 Feb 91 20:00:09 GMT
References: <11474@uhccux.uhcc.Hawaii.Edu>
Sender: daemon@athena.mit.edu (Mr Background)
Organization: The Internet
Lines: 25

No, it's not _really_ a bug in X.  The problem is that there is a
maximum request length that is implicitly used by all the output
functions.  The protocol document (X Window System, 2nd edition, page
382) guarantees this value is at least 4096 4 byte units (i.e.
16KBytes).  It is established at connection time and each server is
free to implement any value larger than 4096.  There is no function or
macro to get this from the display structure.

What this means is that one is allowed to send less than 2000
rectangles per request XDrawRectangles() (each XRectangle structure is
8 bytes plus some overhead for the packet).  There are similar
implicit sizes for XDrawPoints, XDrawLines, XDrawArcs, etc.

To forestall further questions, in general, Xlib cannot breakup such
requests into multiple calls because the requests may depend on
previous values.  For example:
	XDrawPoints	coord mode
	XDrawLines	joins, intersections, coord mode
	XDrawRectangles	no reason
	XDrawArcs	intersections

--pete
Pete Ware / Biosym / San Diego CA / (619) 546-5532
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