h = figure;
axis([0 10 0 10])
hold on
button = 1;
n = 0;
xy_org = [];
while button == 1  % 輸入數據點，以右鍵作結
    [xi,yi,button] = ginput(1);
    plot(xi, yi, 'r+');
    n = n + 1;
    xy_org(:,n) = [xi;yi];
end
pause;% 輸入完畢后按任意鍵繼續

button = 1;
m = 0;
s = zeros(1,2);
pre_m = 0;
while button == 1 % 選擇數據點，以右鍵作結
    while button == 1 && m < 2 
        [xi,yi,button] = ginput(1);
        [d, ind] = min(sum((repmat([xi;yi],1,n) - xy_org).^2)); % 求各數據點與當前鼠標點的最小距離
        if d <= 0.1
            if pre_m ~= 0 % 之前畫過直線，要刷新一下屏幕
                plot(xy_org(1,s(:)), xy_org(2,s(:)), 'wo');
                plot(xy_org(1,s(:)), xy_org(2,s(:)), 'w');
                plot(xy_org(1,s(:)), xy_org(2,s(:)), 'r+');
                pre_m = 0;
            end
            plot(xy_org(1,ind), xy_org(2,ind), 'bo');
            m = m + 1;
            s(m) = ind;
        end
    end
    if m == 1
        plot(xy_org(1,s(m)), xy_org(2,s(m)), 'wo');
        plot(xy_org(1,s(m)), xy_org(2,s(m)), 'r+');
    elseif m == 2
        plot(xy_org(1,s(:)),xy_org(2,s(:)), 'g');
    end
    pre_m = m;
    m = 0;
end
hold off;