Re: rgbplot composite fails with gnuplot

[Juan Pablo Carbajal]

On Tue, Dec 16, 2014 at 5:04 PM, Ben Abbott <address@hidden> wrote:
>
>> On Dec 16, 2014, at 10:56 AM, Juan Pablo Carbajal <address@hidden> wrote:
>>
>> 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.
>
> Does this produce an image with the proper height displayed (i.e. the y 
> extent is from 0.5 to 1.5)?
>
> Ben
>

It was a little tricky cause gnuplot puts the origin in the middle of
the first pixel, not in the corner.
I think this patch fixes the issue. Could you verify and if so apply?

1dimages_gnuplot.diff
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