How keep the length-width ratio of the on-top text fixed in Qt3D

[wang_qt]

From the above figures, you can see that the length-width ratio of the on-top text is changed as change that of the window. How to keep the length-width ratio of the on-top text fixed? Thank you.

The source code is put in
https://drive.google.com/file/d/1oagZhCfVKvCooEev7Vo4XC8q-PAF8aTq/view?usp=sharing

This project is created by Qt creator, and the related code can be found in void OnTopTextDisplay(Qt3DCore::QEntity *rootEntity) in main.cpp.

The on-top effect is realized through GLSL.

Thank you in advance.