@Ejok88 Hi
I used the the book of shaders site tutorials to create the fuzzy circle check here https://thebookofshaders.com/
I actually got a very simple idea for your problem, just use a line with width which is just nothing more that a rectangle with two colors on the edjes, and use GL_TRIANGLE_STRIP , see this new example https://bitbucket.org/joaodeusmorgado/opengltutorials/src/master/T11_FuzzyLine/mygl.cpp#lines-185
Then you just add vertices to compose your line, note that you have to use "two" lines side by side to make the double fade out effect. Then you need to add 3 more lines without width, to the center and the 2 lines in the extremes. A bit of work but doable. I can help further if you need, but right now I just to much work overloaded. What is your use case, are you using widgets and Opengl ? I think going with quick3d would be easier, it that is an option for you.