scalebar(varargin)

function h = scalebar(varargin)
%SCALEBAR creates a scalebar on an axes
%
% SCALEBAR
% SCALEBAR OFF
% SCALEBAR(PARAMETER, VALUE, ...)
% SCALEBAR(HAXES, PARAMETER, VALUE, ...)
% H = SCALEBAR(...)
% 
% Draws a scalebar on the axes and returns handle to the scalebar. The
% DataAspectRatio property of the axes must be set to [1 1 1] and the view
% must be in 2D. All parameters are optional (note the default values
% below). SCALEBAR OFF deletes the current scalebar.
% 
% PARAMETER/VALUE pairs
%     hAxes:        handle to the axes (defaults to current axes)
%     ScaleLength:  length to show (in data units) (defaults to ~10% of the 
%                       x-axis limit range)
%     ScaleLengthRatio: ScaleLength/range(XLim)
%     Location:     location of the scalebar. Possible values are
%                       northeast (default)
%                       northwest
%                       southeast
%                       southwest
%                       [x y] data coordinates
%     Colour:       colour of scalebar in 1x3 RGB array (default is [0 0 0])
%     Bold:         draw with bold text and linewidth=2. 
%                       True or false(default)
%
% Note: SCALEBAR sets the XLimMode and YLimMode of the axes to manual.
%
% Created 10 November 2009 by Amanda Ng

    % DELETE SCALEBAR IF ONE EXISTS
    delete(findobj(gca,'tag','scalebar'));

    % RETURN IF 'OFF' WAS REQUESTED
    if nargin>0 && strcmpi(varargin{1},'off')
        return;
    end

    % CONSTANTS
    directions = {'northwest','northeast','southeast','southwest'};
    
    % SET PARAMETERS TO DEFAULTS
    hAxes = gca;
    scalelength = 0;
    scalelengthratio = 0.1;
    location = 'northeast';
    colour = [0 0 0];
    linewidth = 0.5;
    fontweight = 'normal';

    % PROCESS ARGUMENTS
    if nargin>0
        args = {};
        % Process if arguments given as "hAxes, ..."
        if ishandle(varargin{1}) %hAxes
            args{length(args)+1}='hAxes';
            args{length(args)+1}=varargin{1};
            varargin = varargin(2:end);
        end
        args=[args varargin];
        % Process arguments
        for n=1:2:length(args)
            parameter = args{n};
            value = args{n+1};
            switch lower(parameter)
                case 'haxes'
                    if ~ishandle(value)
                        error 'HAXES is not a valid Axes handle'
                    elseif ~strcmpi(get(value,'type'),'axes')
                        error 'HAXES is not a valid Axes handle'
                    elseif strcmpi(get(value,'tag'),'colorbar')
                        error 'HAXES is a handle to a colorbar'
                    else
                        hAxes = value;
                    end
                case 'scalelength'
                    if ~isnumeric(value)
                        error 'SCALELENGTH must be a numeric value'
                    end
                    scalelength = value;
                case 'scalelengthratio'
                    if ~isnumeric(value)
                        error 'SCALELENGTHRATIO must be a numeric value'
                    end
                    scalelengthratio = value;
                case 'location'
                    if ~(numel(value)==2 && isnumeric(value)) && ...
                       isempty(strmatch(lower(value),directions,'exact'))
                        error 'unrecognised value for LOCATION'
                    end
                    location = value;
                case 'colour'
                    if numel(value)~=3 || ~isnumeric(value)
                        error 'COLOUR must be a 1x3 representation of an RGB colour'
                    end
                    colour = value;
                case 'bold'
                    if ischar(value) && strcmpi(value,'true') || ...
                       (islogical(value) || isnumeric(value)) && value
                            linewidth=2;
                            fontweight='bold';
                    end
                otherwise
                    error(['unrecognised parameter: ' parameter]);
            end
        end
    end

    % CHECK IF DATAASPECTRATIO IS [1 1 1]
    if ~all(get(hAxes,'DataAspectRatio')==1)
        error 'The Axes property DataAspectRatio must be set to [1 1 1]'
    end
    
    % CHECK IF VIEW IS IN 2D
    [az el] = view(hAxes);
    if el~=90
        error 'The Axes must be in 2D view'
    end
    
    %GET IMAGE AND AXES DATA
    axeslims = [get(hAxes,'xlim')' get(hAxes,'ylim')'];
    axesdir = [1 1];
    if strcmpi(get(hAxes,'XDir'),'reverse')
        axeslims(:,1) = flipud(axeslims(:,1));
        axesdir(1) = -1;
    end
    if strcmpi(get(hAxes,'YDir'),'reverse')
        axeslims(:,2) = flipud(axeslims(:,2));
        axesdir(2) = -1;
    end

    % CALCULATE SCALELENGTH
    if scalelength==0
        sl = range(axeslims(:,1))*scalelengthratio;
        slorder = 10^floor(log10(sl));
        scalelength = round(sl/slorder)*slorder;    
    else
        scalelengthratio = scalelength/range(axeslims(:,1));
    end
    
    %SET UP POSITIONING
    if ischar(location)
        switch location
            case 'northeast'
                anchor = [axeslims(2,1) - axesdir(1)*range(axeslims(:,1))*0.05, ...
                          axeslims(2,2) - axesdir(2)*range(axeslims(:,2))*0.05];
                direction = 'southwest';
            case 'northwest'
                anchor = [axeslims(1,1) + axesdir(1)*range(axeslims(:,1))*0.05, ...
                          axeslims(2,2) - axesdir(2)*range(axeslims(:,2))*0.05];
                direction = 'southeast';
            case 'southwest'
                anchor = [axeslims(1,1) + axesdir(1)*range(axeslims(:,1))*0.05, ...
                          axeslims(1,2) + axesdir(2)*range(axeslims(:,2))*0.05];
                direction = 'northeast';
            case 'southeast'
                anchor = [axeslims(2,1) - axesdir(1)*range(axeslims(:,1))*0.05, ...
                          axeslims(1,2) + axesdir(2)*range(axeslims(:,2))*0.05];
                direction = 'northwest';
        end    
    else
        anchor = location;
        if location
            dirToCentre = min(axeslims)+range(axeslims)/2 - location.*axesdir;
            direction = directions{ceil((-1*atan2(dirToCentre(2),dirToCentre(1))+pi)/(2*pi)*4)};
        end
    end

    linepos = [anchor; anchor];
    if ~isempty(strfind(direction,'east'))
        linepos(2,1) = linepos(2,1)+axesdir(1)*scalelength;
    else
        linepos(1,1) = linepos(1,1)-axesdir(1)*scalelength;
    end
    
    ends(:,:,1) = [linepos(1,:); linepos(1,:)];
    ends(:,:,2) = [linepos(2,:); linepos(2,:)];
    if ~isempty(strfind(direction,'north'))
        ends(2,2,:) = ends(2,2,:)-axesdir(2)*0.1*scalelength;
        textalignment = {'bottom', 'center'};
    else
        ends(2,2,:) = ends(2,2,:)+axesdir(2)*0.1*scalelength;
        textalignment = {'top', 'center'};
    end
            
    % DRAW SCALEBAR
    set(gca,'xlimmode','manual','ylimmode','manual');
    hg = hggroup('tag','scalebar');
    line(linepos(:,1), linepos(:,2), 'color', colour, 'linewidth', linewidth, 'parent', hg);
    line(ends(:,1,1), ends(:,2,1), 'color', colour, 'linewidth', linewidth, 'parent', hg);
    line(ends(:,1,2), ends(:,2,2), 'color', colour, 'linewidth', linewidth, 'parent', hg);
    text(linepos(1,1),linepos(1,2),0,'0','verticalalignment',textalignment{1},'horizontalalignment',textalignment{2}, 'color', colour, 'fontweight', fontweight, 'parent', hg);
    text(linepos(2,1),linepos(2,2),0,num2str(scalelength),'verticalalignment',textalignment{1},'horizontalalignment',textalignment{2}, 'color', colour, 'fontweight', fontweight, 'parent', hg);
    
    if nargout>0
        h = hg;
    end
    
    % SETUP DELETE CALLBACK
    set(hg,'DeleteFcn',@deleteScaleBar)
    
    % SETUP LISTENER TO RESET SCALEBAR ON CHANGE OF AXES LIMITS
    hL(1) = addlistener(hAxes,'YLim','PostSet',@(src,event) resetScaleBar(src,event,hg));

    % SET USERDATA
    udata = {'ScaleLengthRatio',scalelengthratio;...
             'AnchorRatio',[(anchor(1)-min(axeslims(:,1)))/range(axeslims(:,1)) (anchor(2)-min(axeslims(:,2)))/range(axeslims(:,2))];...
             'Colour',colour;...
             'Listeners',hL};
    set(hg,'UserData',udata);    
    
    % CALLBACK FUNCTIONS
    function deleteScaleBar(src,event)
        udata = get(src,'UserData');
        delete(udata{strcmpi(udata(:,1),'Listeners'),2});

    function resetScaleBar(src,event,SB)
        udata = get(SB,'UserData');
        hAxes = get(SB,'parent');
        
        delete(SB);        
        
        axeslims = [get(hAxes,'xlim')' get(hAxes,'ylim')'];
        
        scalelengthratio = udata{strcmpi(udata(:,1),'ScaleLengthRatio'),2};
        anchorratio = udata{strcmpi(udata(:,1),'AnchorRatio'),2};
        location = [anchorratio(1)*range(axeslims(:,1))+axeslims(1,1) anchorratio(2)*range(axeslims(:,2))+axeslims(1,2)];
        colour = udata{strcmpi(udata(:,1),'Colour'),2};
        
        scalebar(hAxes,'ScaleLengthRatio',scalelengthratio,'Location',location,'Colour',colour);