I would like to welcome guest writer Takeshi (Kesh) Ikuma. Kesh has posted several interesting utilities on the Matlab File Exchange, including the award-winning Enhanced Input Dialog Box. Today, Kesh will describe how we can automate GUI actions programmatically.
Automating GUI actions, including controlling a mouse and keyboard programmatically, is often useful. This can be used, for example, to demonstrate GUI usage or to perform a recorded macro.
Matlab’s Handle Graphics interface provides a simple way to manipulate the mouse cursor position, but not to emulate mouse or keyboard clicks. However, we can utilize Java’s java.awt.Robot class.
This article provides an overview of the Robot class and how it can be used to program mouse movement, button clicks and keyboard strikes.
The online Java documentation describes the purpose of the Robot class as follows:
This class is used to generate native system input events for the purposes of test automation, self-running demos, and other applications where control of the mouse and keyboard is needed.
This class has three main functionalities: mouse control, keyboard control, and screen capture. Here are some of the important member functions:
Mouse control functions
void mouseMove(int x, int y)
This function moves the cursor to the coordinate (x, y) which is defined with respect to the top-left screen corner (in contrast to Matlab’s coordinate origin at the bottom-left corner).
void mousePress(int buttons)
void mouseRelease(int buttons)
This pair of functions performs the button click. Their input argument is an OR’ed combination of java.awt.event.InputEvents:
java.awt.event.InputEvent.BUTTON1_MASK // left mouse button java.awt.event.InputEvent.BUTTON2_MASK // middle mouse button java.awt.event.InputEvent.BUTTON3_MASK // right mouse button
Keyboard control functions
Keyboard action is emulated by the following pair of functions. Their keycodes are defined in java.awt.event.KeyEvent:
void keyPress(int keycode)
void keyRelease(int keycode)
NOTE: Although java.awt.event.KeyEvent constants defines most of the US QWERTY keys, not all can actually be used with java.awt.Robot. Specifically, it appears that only the KeyEvent constants for unmodified keys can be used. See the following section for an example.
The robot can be put to sleep for a desired duration (in milliseconds). Also, the calling routine can be blocked until the robot exhausts its command queue.
void delay(int ms)
Readers interested in Robot’s screen-capture capability are invited to take a look at Yair’s ScreenCapture utility on the File Exchange.
Using java.awt.Robot in Matlab
To create the Robot object in Matlab, simply run
robot = java.awt.Robot;
Moving the mouse cursor
With Matlab’s root (0) handle, the mouse cursor can be repositioned by
The mouse cursor is placed on the x-th pixel from left edge and the y-th pixel from the bottom edge of the screen.
Alternately, we could use the semi-documented moveptr function, which was described here last year.
The same operation can also be done using Robot as follows:
scrSize = get(0,'ScreenSize'); robot.mouseMove(x,scrSize(2)-y);
The extra step must be taken to convert from Matlab to Java screen coordinates.
Depending on the specific case (for example, whether or not we know the absolute or only relative screen coordinates), we may prefer using any of these equivalent mouse-movement alternatives.
Clicking mouse buttons
Unfortunately, we have few alternatives for automating mouse-clicks – Robot is basically our only option. Matlab recognizes 4 different mouse click types as specified in the Figure’s SelectionType property:
- Normal: Click left mouse button
- Extend: SHIFT-click left mouse button
- Alternate: CTRL-click left mouse button
- Open: Double click left mouse button
To observe the mouse click, open a figure and set its WindowButtonDownFcn callback:
myCallback = @(hObj,event) disp(get(hObj,'SelectionType')); set(gcf,'WindowButtonDownFcn', myCallback);
To trigger the callback, the figure must have the focus and the mouse cursor must be on the figure. To ensure the callback invocation, “figure(gcf); drawnow;” commands are included in the code examples below. Make sure to place the mouse cursor on the figure before running these codes.
Here’s how the Robot can be used to perform each type of clicking. First, normal click:
figure(gcf); drawnow; robot.mousePress (java.awt.event.InputEvent.BUTTON1_MASK); robot.mouseRelease(java.awt.event.InputEvent.BUTTON1_MASK);
For “open” or double click, repeat it twice:
figure(gcf); drawnow; robot.mousePress (java.awt.event.InputEvent.BUTTON1_MASK); robot.mouseRelease(java.awt.event.InputEvent.BUTTON1_MASK); robot.mousePress (java.awt.event.InputEvent.BUTTON1_MASK); robot.mouseRelease(java.awt.event.InputEvent.BUTTON1_MASK);
For the other two click types, we need to use the keyboard functions. First, “extend” or SHIFT-click:
figure(gcf); drawnow; robot.keyPress (java.awt.event.KeyEvent.VK_SHIFT); robot.mousePress (java.awt.event.InputEvent.BUTTON1_MASK); robot.mouseRelease(java.awt.event.InputEvent.BUTTON1_MASK); robot.keyRelease (java.awt.event.KeyEvent.VK_SHIFT);
Lastly, “alternate” or CTRL-click:
figure(gcf); drawnow; robot.keyPress (java.awt.event.KeyEvent.VK_CONTROL); robot.mousePress (java.awt.event.InputEvent.BUTTON1_MASK); robot.mouseRelease(java.awt.event.InputEvent.BUTTON1_MASK); robot.keyRelease (java.awt.event.KeyEvent.VK_CONTROL);
Clicking keyboard keys
Just as we have shown above how to press a modifier key (Ctrl or Alt key) to set the figure’s SelectionType property, keyPress and keyRelease functions can be used with character keys to type text. For example, with the focus on Matlab’s Command Prompt, running the following code executes the ver command:
robot.keyPress (java.awt.event.KeyEvent.VK_V); robot.keyRelease (java.awt.event.KeyEvent.VK_V); robot.keyPress (java.awt.event.KeyEvent.VK_E); robot.keyRelease (java.awt.event.KeyEvent.VK_E); robot.keyPress (java.awt.event.KeyEvent.VK_R); robot.keyRelease (java.awt.event.KeyEvent.VK_R); robot.keyPress (java.awt.event.KeyEvent.VK_ENTER); robot.keyRelease (java.awt.event.KeyEvent.VK_ENTER);
In the previous section, I mentioned that not all KeyEvent constants are supported by java.awt.Robot, and keys must be defined with their unmodified characters. For example, a semicolon (‘;’) can be typed by:
robot.keyPress (java.awt.event.KeyEvent.VK_SEMICOLON); robot.keyRelease (java.awt.event.KeyEvent.VK_SEMICOLON);
However, doing the same for a colon (‘:’ or SHIFT-‘;’) causes an error:
robot.keyPress (java.awt.event.KeyEvent.VK_COLON); robot.keyRelease (java.awt.event.KeyEvent.VK_COLON); ??? Java exception occurred: java.lang.IllegalArgumentException: Invalid key code at sun.awt.windows.WRobotPeer.keyPress(Native Method) at java.awt.Robot.keyPress(Unknown Source)
Instead of using the VK_COLON constant, VK_SEMICOLON constant must be used while SHIFT modifier key is pressed:
robot.keyPress (java.awt.event.KeyEvent.VK_SHIFT); robot.keyPress (java.awt.event.KeyEvent.VK_SEMICOLON); robot.keyRelease (java.awt.event.KeyEvent.VK_SEMICOLON); robot.keyRelease (java.awt.event.KeyEvent.VK_SHIFT);
Although unconfirmed, I suspect VK_SEMICOLON constant would not work with keyboards in which semicolon is mapped to SHIFT-‘,’ (e.g., Spanish or Italian keyboard layouts), while the VK_COLON constant would work with a French keyboard.
Putting it all together: jMouseEmu and inputEmu
To simplify the execution of the mouse and keyboard actions outlined above, I (Kesh Ikuma) have created the jMouseEmu and inputEmu utilities, which are available on the Matlab File Exchange. These interface/wrapper functions will be described in next week’s article.
Do you have any favorite use for Java Robots in your workflow? If so, please tell us all about it in a comment below.
Very interesting. I used this java.awt.Robot class recently to perform GUI testing in MATLAB and, with little effort, it became a very interesting and simple feature to use.
Thanks for posting
“Although unconfirmed, I suspect VK_SEMICOLON constant would not work with keyboards in which semicolon is mapped to SHIFT-’,’ ”
I can confirm that this is true (writting from a danish laptop). At my computer ‘;’ is mapped to ‘,’ and so to generate a semicolon it works to write the following in MATLAB:
Great article! Thanks for posting 🙂
I try this example some time ago from another source. Now I´m reading all your posts to learn new things (great job). When I reach newer posts I will ask you some things I want to do and don´t know how.
Just like you have given the commands for keyboard and mouse interface is there any command for joystick interface in java. Please help.