To present stimuli for my experiments in the lab, I use Psychophysics Toolbox (Psychtoolbox) in conjunction with Matlab.

One limitation of Psychtoolbox is that the included DrawFormattedText function does not allow text to be horizontally  centered on a point other than the horizontal center of the screen. That frustration doesn’t seem to make much sense, but what I mean by it is that you cannot offset the centering (as you could by choosing to centering within different columns of a table) – If you try and place the text anywhere other than the horizontal center of the screen, the text must be left-aligned.

This means that, when using the original DrawFormattedText,  instead of nice-looking screens like this:

you get this:

which is a little messy.

To fix this, I have modified the  DrawFormattedText file to include an xoffset parameter. It’s a very basic modification, that allows text to be centered on points offset from the horizontal center of the screen.  For example, calling DrawFormattedText_mod with:
1) xoffset set to -100, centers text horizontally on a point 100 pixels to the left of the horizontal center of the screen.
2) xoffset set to rect(3)/4 (where rect = Screen dimensions e.g. [0 0 1024 768]), centers text horizontally 1/3 of the way from the left hand edge.
I haven’t replaced my DrawFormattedText.m with my DrawFormattedText_mod.m just yet, but it has been added to the path and seems to be doing the trick.

You can download my DrawFormattedText_mod.m here: https://dl.dropbox.com/u/4127083/Scripts/DrawFormattedText_mod.m