MATLAB: How to Execute Something When a Graphics Object is Left-Clicked

graphics objectleft click

I want the red rectangle to turn green when I only “left-click” (not right-click or middle click) on it. What is the easiest solution?

hax = axes('XLim', [0 4], 'YLim', [0 4]);
r = rectangle('Position', [1 1 1 1], 'FaceColor', 'r');

Best Answer

function test
FigH = figure;
hax = axes('XLim', [0 4], 'YLim', [0 4]);
r = rectangle('Position', [1 1 1 1], 'FaceColor', 'r', ...
              'ButtonDownFcn', {@RectClickCB, FigH});
function RectClickCB(RectH, EventData, FigH)
switch get(FigH, 'SelectionType')
case 'normal'  % Left click
  set(RectH, 'FaceColor', 'g');
case 'alt'     % Right click
case 'extend'  % Middle click
otherwise
  ...
end

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MATLAB: Does “ginput” return points the left axes generated by “plotyy” even though I have set the right axes as the current axes

This is expected behavior. The reason "ginput" is providing you with information from the left axes even when you have set the right axes as the current axes is because of the way the axes properties are set by "plotyy"; "plotyy" sets the right axes as not-selectable. A workaround to make sure that the right axes is used instead of the left axes when selecting it with "ginput" is to include the following two commands:

>> set(Ax(2),'HitTest','on')

>> set(Ax(1),'HitTest','off')

This will make the right axes selectable and left axes not selectable when using "ginput". Below is a more detailed explanation of what causes this expected behavior.

The "plotyy" function superimposes two axes on top of each other so as to display two different pieces of information. In doing so, it determines that the left axes will be the ones to be display on top of the right axes. In order for this to happen, it sets the 'HitTest' property of the left axes to 'on', while that of the right axes to 'off'. This property determines if the axes is selectable by the mouse click. As you can see, setting the "background" axes 'HitTest' property to 'off' makes sure the axes cannot be selected by the mouse. Here is a link to the documentation that talks about the different properties for an axes. There you will find that for 'HitTest':

http://www.mathworks.com/help/releases/R2014a/matlab/ref/axes_props.html

The result of these settings mean that when you click on a particular location using "ginput" you are actually clicking on the left axes even though you have told MATLAB that the right axes is the current one. You can also verify this via two methods:

1) You can get the 'HitTest' property of each of the axes and identify that the right axes is set to 'off', while that of the left axes is set to 'on'.

2) You can use "ginput" to select on the red plot line that corresponds to the right axes and you will see the result is a y-value in the righ axes coordinates. This is because although the right axes 'HitTest' property is 'off', that same property for its plot line is set to 'on'. In other words, although the axes is not selectable the plot line itself is.

MATLAB: Hovering on an Graphics Object

As a rough guide:

axesPos = getpixelposition( hax );
rectXPos = [1 2] / 4 * axesPos(3) + axesPos(1);
rectYPos = [1 2] / 4 * axesPos(4) + axesPos(2);

Then you will need to use the

WindowButtonMotionFcn

of the figure and create a function that tests the figure's

CurrentPoint

property against those rectXPos and rectYPos to see if you are inside the rectangle or not. The callback syntax will need to be something like

hFig.WindowButtonMotionFcn = @(src,evt) motionFunc( src, rectXPos, rectYPos );

and a function syntax e.g.

funcion motionFunc( hFig, rectXPos, rectYPos )
currentPoint = hFig.CurrentPoint;
% Do the obvious maths here of cyrrentPoint(1) against rectXPos and currentPoint(2) against rectYPos

I've probably missed out one or two things as I don't have time to give a full answer, but you should get the idea. Obviously the hard coded numbers in the recXPos and rectYPos maths should be replaced by calculations based on your rectangle position and axes limits rather than hard-coded.

If you allow zooming then these will need to be calculated dynamically because the XLim and YLim will change.

Best Answer

Related Solutions

MATLAB: Does “ginput” return points the left axes generated by “plotyy” even though I have set the right axes as the current axes

MATLAB: Hovering on an Graphics Object

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