how to count visible lines in textArea?

I have a long text in Text Area, which is too long to fit. As the app window and the text area is changing size (possibly also font size), the text is partially hidden. I'd like to know, how many lines of text are actually visible.

Answer 1

[Image Analyst]

I'd take a vertical profile and threshold it. You forgot to attach your picture. But if you have an image with black text on a white background

verticalProfile = mean(grayImage, 2);
mask = verticalProfile < 128;
[labeledLines, numberOfLines] = bwlabel(mask)

[Jiri Hajek]

This is an interesting idea, but I'm not sure if it can be directly applied to an uiTextArea, which is not an image, but a live text field. It is further embedded into an app, which has many more components (buttons, labels, text fields, axes, tabs), so to analyze the app GUI as an image would be difficult, although perhaps viable using "exportapp" function.

My information readily available is the text content as a cell array and properties of the uiTextArea, which I hoped could be sufficient. Perhaps I could make an analysis of a sample text to get an approximate relationship between the size in pixels, font size and number of visible lines...