Friday, July 3, 2009

Topic #2 (Part1): Matlab GUI

Taking a little detour from HDL, I would like to discuss the second topic, which concerns the engineering programming/scripting language called Matlab. Practically all electrical/computer engineers have encountered Matlab at some point of their studies. For those less familiar with it, Matlab is a Matrix laboratory that serves as an excellent tool for visualization of engineering problems. Having a strong background can be a huge benefit when it comes to applying for a job concerning research/developement in an electrical/computer engineering field. In this topic, I would like to discuss the methods of creating a GUI without the aid of Matlab's GUI creator GUIDE.

The most fundamental component to creating a GUI in Matlab is the "handle". It is critcal to GUI creation that you fully understand what a handle is, so I will take this very slow. As the name suggests, a handle is a component of an object that you "can grab onto", basically meaning it serves as a unique identifier in the environment that you can call, set, and get different properties. Each time a handle is created Matlab generates a new value that is not in use. In the simplest case you might create a figure by issuing the command:


By dowing this, Matlab creates a handle value of 1 that is used to control the newly created figure window. If two other windows are created after this, where the handle value is not set, matlab will auto-increment to the next unused value. Thus, issueing the command figure twice after figure(1) would yeild two new figure windows one which has a value of 2 and the other a value of 3. If however, before calling that third figure window I were to close/delete the first figure (which has a handle value of 1), that third figure command would recreate the handle value of 1 instead of continuing with the incrementing scheme. Note: these integer handle values are generally reserved for figure windows, other object will generally use floating point but you can manually assign a handle of either integer or double depending on your needs/preference. Whenever an object is being created, such as a figure, an axes, a uicontrol, etc the programmer can choose to store the handle value into a variable to easily reference that object at a later time. For instance:


The commands above would create a figure of some handle value that gets stored into the variable 'a' and an axes figure inside that figure with a handle value storing in b. This makes referenceing each individual object much more simple than finding parent/daughter objects.

Now that we have a good idea of how handles can be used lets introduce some of the most usefull commands that can be used with these handle values.

The "get" command: used to grab all object properties from a handle, or a specific property value.

The "set" command: used to set a property value of a handle.

The "findobj" command: used to find all handles that have a property set to a specific value.

The "uicontrol" command: used to create I/O objects such as radio buttons, pushbuttons, textboxes, etc.

Use the "help" command to learn more about these functions. This is all for now. Next time, I will discuss callback functions and how to create an event based GUI.

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