[Octave-bug-tracker] [bug #48879] imagesc plotting is incorrect with OpenGL toolkit

[Rik]

URL:
  <http://savannah.gnu.org/bugs/?48879>

                 Summary: imagesc plotting is incorrect with OpenGL toolkit
                 Project: GNU Octave
            Submitted by: rik5
            Submitted on: Tue 23 Aug 2016 03:52:53 PM PDT
                Category: Plotting with OpenGL
                Severity: 4 - Important
                Priority: 5 - Normal
              Item Group: None
                  Status: None
             Assigned to: None
         Originator Name: 
        Originator Email: 
             Open/Closed: Open
         Discussion Lock: Any
                 Release: dev
        Operating System: Any

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Details:

The algorithm for scaled cdata is supposed to be


index = fix((C-cmin)/(cmax-cmin)*m)+1;
%Clamp values outside the range [1 m]
index(index<1) = 1;
index(index>m) = m; 


Matlab and the gnuplot toolkit correctly implement that.

For qt and fltk toolkits, the 'round' function, instead of 'fix', seems to be
used.


index = round((C-cmin)/(cmax-cmin)*m)+1;
%Clamp values outside the range [1 m]
index(index<1) = 1;
index(index>m) = m; 


I've added a new demo (#5) to imagesc that shows this.  Try


demo imagesc 5







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