[Rd] x11 colortype problems ('gray' is broken?) (PR#512)

[Prof Brian D Ripley]

On Fri, 7 Apr 2000 tov@ece.cmu.edu wrote:

> 
> Hi,
> 
>   I occasionally run out of color in my X11 terminal.  At this
> point, R will issue this error message:
>         Error: X11 cannot allocate additional graphics colors.
> Consider using colortype="pseudo.cube" or "gray".
> 
> An immediate x11(colortype="pseudo.cube") doesn't work as the
> colortype seems to be shared among the different x11 plotting windows.
> So I have to close all windows first, then I can open an x11 device
> with the colortype "pseudo.cube".  (Neither the necessity to close all
> windows nor the fact, that colortype is an option to X11 and not to
> the plot command, is clear from the help pages or the error message.)

There is a single colortype shared by all x11 devices.  That couild eb
clearer!

> The real problem, however, comes with x11(colortype="gray") as this
> brings up just a black screen (and it stays black).  I can't quite see
> whether I'm stumbling across some issues with X resources, here.
> x11() usually gives a white background.

No. It's a bug.  When you set x11(colortype="gray") it tries to allocate
min(256, 2^depth) colours, that is all the colours on an 8-bit display.
That is clearly going to fail (unless perhaps your window manager is 
in mono).  So it does fail, set PaletteSize = 0, and then maps all
colours to black.  That's what the x11 driver seems to do when colour
allocation fails.  I suspect it should not open at all under those 
circumstances.

Quick fix:

static void SetupGrayScale()
{
    PaletteSize = 0;
    if (depth > 7)
	depth = 7;
    if (GetGrayPalette(display, colormap, 1 << depth) == 0)
	depth = 1;
}

(8 replaced by 7) in devX11.c.  I'll commit a more sophisticated one
to R-release.


-- 
Brian D. Ripley,                  ripley@stats.ox.ac.uk
Professor of Applied Statistics,  http://www.stats.ox.ac.uk/~ripley/
University of Oxford,             Tel:  +44 1865 272861 (self)
1 South Parks Road,                     +44 1865 272860 (secr)
Oxford OX1 3TG, UK                Fax:  +44 1865 272595

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