Re: few remarks

[Dave D. <dde...@es...>]

Daniel J Sebald <dan...@ie...> writes:

> Dave Denholm wrote:
>
>>Ethan Merritt <merritt@u.washington.edu> writes:
>>
>>
>>>On Monday 09 August 2004 11:04 pm, mi...@ph... wrote:
>>>
>>>>Bug:
>>>>On x11 (well, I haven't look to other terminals), points in the points and
>>>>linepoints styles are "handicapped" -- look by a screen magnificator (xmag,
>>>>kmag) to points obtained by:
>>>>
>>>>set size ratio 1
>>>>plot sin(x)/x w point pt 2
>>>>
>>>That is one strange bug you have found.  The odd thing is that it seems
>>>to be a bug in the X server.   I can run the same gnuplot_x11 executable
>>>on two different machines and get two different results.  My best guess
>>>at the moment is that the key difference is which version of X11 is
>>>running, although it is also possible that it is a difference in the video
>>>driver rather than the version.  The issue is whether the rendering
>>>engine does, or does not, draw the final pixel in a line segment that is
>>>at 45 degrees. Changing the drawing style from CapButt to CapRound
>>>while drawing points fixes this, at least on the machines I have tested.
>>>I can't think of any bad effects from this so I will make the change.
>>>I'm sure someone will speak up if it uncovers some complementary
>>>bug on other X11 display setups.
>>>
>>>
>>
>>
>>Does gnuplot use zero-width lines for these ?  I have a vague
>>recollection that if linewidth is set to 0, the X server can use a
>>device-specific algorithm for drawing the pixels. A linewidth of 1
>>specifies the exact semantics which must be followed.
>>
>>
>>Yeah - looks like :
>>
>>	else if (*buffer == 'P') {
>>	    /* linux sscanf does not like %1d%4d%4d" with Oxxxxyyyy */
>>	    /* sscanf(buffer, "P%1d%4d%4d", &point, &x, &y); */
>>	    point = buffer[1] - '0';
>>	    sscanf(buffer + 2, "%4d%4d", &x, &y);
>>	    if (point == 7) {
>>		/* set point size */
>>		px = (int) (x * xscale * pointsize);
>>		py = (int) (y * yscale * pointsize);
>>	    } else {
>>		if (type != LineSolid || width != 0) {	/* select solid line */
>>		    XSetLineAttributes(dpy, gc, 0, LineSolid, CapButt, JoinBevel);
>>		}
>>
>>
>>- try setting the linewidth param to 1 in the XSetLineAttributes call.
>>
>
> I printed out the numbers and verified that
>
> plot->lwidth
>
> is 1.  I've concluded, like Ethan, that the behavior of this routine
> doesn't match what the documentation says.  (It's as though there is
> some confusion between CapButt and CapNotLast.)  Also, I think
> CapRound, i.e. the endpoints of the lines are rounded when they get
> thicker would look just as good as not rounding when dealing with
> symbols.
>

Sorry, I should have been clearer. I don't mean the gnuplot line
width. I mean the X linewidth set into the GC when drawing the symbol.

X allows a linewidth of 0 to mean a fast line draw, not necessarily
conforming to all the specs. ie it is allowed to be different on
different X servers.

You need to set the X GC linewidth to 1 to get a fully-conforming
line.

dd
-- 
Dave Denholm              <dde...@es...>       http://www.esmertec.com