cursorUpdater.m

function fhndl = cursorUpdater(cursors)

if nargin<1 || isempty(cursors)
    fhndl.update        = @(~,~) 1;   % dummy function that swallows arguments and is noop
    fhndl.updateCursors = @(~,~) 1;
    fhndl.reset         = @(~,~) 1;
    return;
end

usingPoly = isfield(cursors,'poly');
cursorPolys = [];
cursorRects = [];
nAOI        = [];
nElemPerAOI = [];
cursorLooks = [];
cursorIdxs  = [];
qCursorReset= [];
cursorReset = [];
updateCursors(cursors);

currCursor  = nan;

fhndl.update        = @update;
fhndl.updateCursors = @updateCursors;
fhndl.reset         = @reset;

    function update(x,y)
        if usingPoly
            idx = [];
            % get in which poly, if any. If polys overlap, first in the
            % list is used
            for p=1:nAOI
                if inPoly([x y],cursorPolys{p})
                	idx = p;
                    break;
                end
            end
        else
            if isempty(cursorRects)
                idx = [];
            else
                % get in which rect, if any. If rects overlap, first in the list is
                % used
                idx = find(inRect([x y],cursorRects),1);
            end
        end
        
        % get corresponding cursor
        if isempty(idx)
            curr = cursorLooks(end);
        else
            curr = cursorLooks(cursorIdxs(idx));
        end
        
        % see if need to change
        if currCursor ~= curr
            if curr==-1
                HideCursor();
            else
                ShowCursor(curr);
            end
            currCursor = curr;
        end
    end

    function updateCursors(cursors)
        % process rects/polys
        usingPoly = isfield(cursors,'poly');
        if usingPoly
            cursorPolys = cursors.poly;
            nAOI        = length(cursorPolys);
            nElemPerAOI = ones(1,nAOI);
        else
            cursorRects = [cursors.rect{:}];
            nAOI        = length(cursors.rect);
            nElemPerAOI = cellfun(@(x) size(x,2),cursors.rect);
        end
        % cursor looks are numbered IDs as eaten by ShowMouse. -1 means hide cursor
        cursorLooks = [cursors.cursor cursors.other];
        cursorIdxs  = SmartVec(1:nAOI,nElemPerAOI,0);
        
        % optional (default on) reset of cursor when calling reset(). Have it as an
        % option as some function out of the reach of the user always call reset
        % upon exit, user can here configure if it actually does something
        qCursorReset = true;
        if isfield(cursors,'qReset')
            qCursorReset = cursors.qReset;
        end
        % if resetting, indicate what cursor to reset to. if empty, we reset to
        % cursors.other.
        cursorReset = [];
        if isfield(cursors,'reset')
            cursorReset = cursors.reset;
        end
    end

    function reset()
        if ~qCursorReset
            return;
        end
        
        if ~isempty(cursorReset)
            curr = cursorReset;
        else
            curr = cursorLooks(end);
        end
        if curr==-1
            HideCursor();
        else
            ShowCursor(curr);
        end
    end

end