Mouse click on Axes Problem

Hello. I am trying to use the mouse click on an axes to drive the position of an xystage. I have created my a grid with identifying text:

axes(handles.axes1); cla reset
hold on
ax = gca;
ax.XGrid = 'on';
ax.YGrid = 'on';

xticks(1:1:13)
yticks([1:1:9])
xlim([1 13]);
ylim([1 9]);

ax.GridColor = [0 .5 .5];
ax.GridLineStyle = '--';
ax.GridAlpha = 0.5;
ax.Layer = 'top';
hold on;

format bank
startingRows = linspace(1, 8, 8);
startingCols = linspace(1, 12, 12);
% % Now get the starting integer rows / cols.
startingRows = int32(startingRows(1:end))
startingCols = int32(startingCols(1:end))
ct=0;
for i=1:length(startingRows)
   for j=1:length(startingCols)    
    ct=ct+1;
    %Add region number
     xr=double(startingCols(j))+0.3;
     yr=double(startingRows(i))+0.5;    
     hold on
     text(xr,yr,[num2str(i),',',num2str(j)],'FontSize', 8, 'Color', [1 0 1]);
   end
end
set(handles.axes1,'Visible','on');
set(handles.axes1,'ButtonDownFcn',@ImageClickCallback);  %An alternative to axes ButtonDownfunction

I then want to be able to click anywhere on the grid and return the number sin the grid. Its fine just to return the coordinates of the mouse. I have tried the axes1 ButtondownFunction via:

axes(handles.axes1)
cpt = get(gca,'CurrentPoint')
pt = cpt(1,1:2)
x=round(pt(1))
y=round(pt(2))

But it only works before the grid and numbers are drawn on. I have read this only works when actually clicking on the grid and not areas inside i.e. the boxes - which is what I want.

Answer 1

[Jan]

It is prone to bugs to rely on the current axes object by cla and gca. You have the handle of the axes available, so use it. Replace:

axes(handles.axes1); cla reset
hold on
ax = gca;

by

ax = handles.axes1;
cla(handles.axes1, 'reset')
ax.NextPlot = 'add';   % EDITED, was 'on'

The format bank influences all following output to the command window. It is not useful here.

Replace

startingRows = linspace(1, 8, 8);
startingRows = int32(startingRows(1:end))

by the much simpler:

startingRows = 1:8;

(1:end) can be omitted at all, because it wastes time only.

I assume, the only problem with your code is, that the text objects shadow the axes, such that a click on them does not trigger the ButtonDownFcn of the axes in the background. You can let the text objects pass through the event by setting their 'HitTest' to 'off':

text(xr, yr, sprintf('%d,%d', i, j), 'FontSize', 8, 'Color', [1 0 1], ...
     'HitTest', 'off');

Summary:

% ** UNTESTED CODE - WRITTEN IN THE FORUMS INTERFACE ONLY **
ax = handles.axes1;
cla(ax, 'reset')
ax.NextPlot = 'on';   % Equivalent to: hold on
ax.XGrid    = 'on';
ax.YGrid    = 'on';

ax.XTick = 1:13;
ax.YTick = 1:9;
ax.XLim  = [1 13];
ax.YLim  = [1 9];

ax.GridColor     = [0 .5 .5];
ax.GridLineStyle = '--';
ax.GridAlpha     = 0.5;
ax.Layer         = 'top';

for i = 1:8
   for j = 1:12
      text(j + 0.3, i + 0.5, sprintf('%d,%d', i, j), ...
           'FontSize', 8, 'Color', [1 0 1], ...
           'HitTest', 'off');
   end
end
ax.Visible = 'on';
ax.ButtonDownFcn = @ImageClickCallback;

And the callback:

function ImageClickCallback(AxesH, EventData)
cpt = get(AxesH, 'CurrentPoint');
pt  = cpt(1, 1:2);
x   = round(pt(1));
y   = round(pt(2));
... what to do with x and y?
end

Using the dot notation "ax.Property = ..." only looks nicer, but is is no error to mix it with "set(ax, 'Property', ...)" and the more abstract functions like xticks and hold on.

[Jason]

Hi Jan, thanks for your advice.

I've run into the following error:

While setting property 'NextPlot' of class 'Axes':
'on' is not a valid value. Use one of these values: 'add' | 'replace' | 'replacechildren' | 'replaceall'.

Error in MicroWell>pushbutton2_Callback (line 196)
ax.NextPlot = 'on';

[Jason]

thats perfect Jan, my issue now is getting the x & y as either normalised coordinates, or from the text in the box.

[Jan]

@Jason: This was a typo. See EDITED: 'on' => 'add'

To get x and y in normalized coordinates:

xn = (x - 1) / 8
yn = (y - 1) / 8

To get the contents of the text objects:

TextH = gobjects(12, 8);
for i = 1:8
  for j = 1:12
    TextH(j, i) = text(j + 0.3, i + 0.5, sprintf('%d,%d', i, j), ...
         'FontSize', 8, 'Color', [1 0 1], ...
         'HitTest', 'off');
  end
end
% Store the handles to the text objects in the UserData of the axes:
ax.UserData = TextH;

and in the callback:

function ImageClickCallback(AxesH, EventData)
cpt = get(AxesH, 'CurrentPoint');
pt  = round(cpt(1, 1:2));
x   = pt(1);
y   = pt(2);
Str = AxesH.UserData(x, y).String
end

Sorry, I cannot test this currently. Maybe x and y have to be interchanged at some places.

[Jason]

what does the following do:

ax.NextPlot = 'add';

[Jan]

@Jason: The same as: hold on , but this uses the current axes. Look into the code of hold:

type hold

You can see, that this does some parsing and sets 'NextPlot' also. So I prefer the direct approach.