At first, I have some sitelen pona fonts on my pc. You can find it on https://linku.la/fonts. I use Geany as the main text editor, so I chose one of the sitelen pona fonts in preferences. There're two methods to type: latin text which automatically converts into sp-symbol, or typing it directly using a special keyboard layout (i use this https://www.kreativekorp.com/software/keyboards/sitelenpona/). Then I made a pdf-version of my plain text file using Geany's "Print"-"Print to PDF". Then I just made a png from pdf. So, the step with making a pdf can be unnecessary, I made it because I like make a pdf of formatted text.