Re: rgbplot composite fails with gnuplot

[Juan Pablo Carbajal]

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.