In jME/Nifty, each letter is basically a Quad with a Texture on it. Scaling font-textures usually looks horrible and I guess that's why Nifty doesn't provide an option for scaling (you can scale
BitmapText in jME though).
Easiest way is to generate a new, bigger font. If you're using the jME SDK there's a built-in generator. Right click on a folder in the Projects Window and choose
New -> Other -> GUI -> Font.
I recommend a padding of 2 for X and Y. Otherwise you might see random dots in the rendered text (these are parts of other letters that are overlapping the letter box in the texture).
Sometimes there's a huge gap between the letters. You can control that by using negative values for "letter spacing".
Nifty's Textfield-Control is a composition of panels and text elements. To use a bigger font you have to redefine its style.
Grab the original
nifty-textfield.xml from your
nifty-style-black.jar or from here: https://github.com/nifty-gui/nifty-gui/blob/1.4/nifty-controls-style-black/src/main/resources/textfield/nifty-textfield.xml
Save it somewhere in your Assets/Interface folder and include it in your other XML like this:
(Make sure to include it after
<useStyles filename="Interface/textfield.xml" />
Now you have to adjust the style. Remove the
base="base-font" attribute from the style with ID
nifty-textfield#text and add
font to the
It should look like this:
<attributes ... font="Interface/Fonts/YourFont-24.fnt" />
You probably also want to change the size of the Textfield to match the new font. Edit the other styles in this file as you need.
The Nifty Manual explains controls and styles in more detail: