Re: rgbplot composite fails with gnuplot

[Juan Pablo Carbajal]

On Tue, Dec 16, 2014 at 4:32 PM, Juan Pablo Carbajal
<address@hidden> wrote:
> On Tue, Dec 16, 2014 at 4:25 PM, Juan Pablo Carbajal
> <address@hidden> wrote:
>> On Tue, Dec 16, 2014 at 3:31 PM, Ben Abbott <address@hidden> wrote:
>>>> On Dec 16, 2014, at 8:26 AM, Juan Pablo Carbajal <address@hidden> wrote:
>>>>
>>>> Tested in 4.1.0+
>>>> repo id 19402:5cd83b466a3e
>>>>
>>>> octave-cli:1> rgbplot(jet(16),'composite')
>>>>
>>>> multiplot> plot "-" binary array=16x2 scan=yx origin=(1,1) dx=1 dy=0
>>>> using 1 title "" with image; ;
>>>>                                                                  ^
>>>>           line 0: Sample period must be positive. Try `flip` for
>>>> changing direction
>>>>
>>>>
>>>> Can anybody reproduce?
>>>>
>>>> Do we report bugs that involve gnuplot?
>>>>
>>>
>>> I get the same result using gnuplot 4.6 patchlevel 6.
>>>
>>> The error is indicating that dy must be greater than 0.  The m-code which 
>>> produces this gnuplot command is in plot/utils/private/__go_draw_axes__.m 
>>> at lines 554-547.
>>>
>>>         titlespec{data_idx} = "title \"\"";
>>>         usingclause{data_idx} = sprintf ("binary array=%dx%d scan=yx 
>>> origin=(%.15g,%.15g) dx=%.15g dy=%.15g using %s",
>>>             x_dim, y_dim, x_origin, y_origin, dx, dy, format);
>>>         withclause{data_idx} = sprintf ("with %s;", imagetype);
>>>
>>> The image intended looks a similar to a colorbar, so I expect the problem 
>>> is on Octave's end.
>>>
>>> Ben
>>
>> Ben,
>>
>> Ok, thanks. I spotted the problem.
>> It happens when when the data of the image has a single row.
>> That is this fails as well
>>
>> image (1:8)
>>
>> The issue comes in lines 513 and 527-529 of __go_draw_axes__.m
>> When dy=0 because the ydata of the image is [1 1]
>>
>> What are the "dx" and "dy" option for plot in gnuplot? I can't find a
>> reference. Knowing that we jnow how to fix the issue.
>
> Ok, found it.
>
> The clause for gnuplot should not contain "dy=" when dy==0 . This
> makes the plot appear but the axis look wrong.
> So the sprintf command should be conditional on the value of dy.

Another solution is to leave the sprintf fixed and set dy=1 when line
530 gives a 0. (the same should be done to dx).
I still do not understand how does gnuplot handles a one dimensional image.