@madskjeldgaard This month I'm almost never at home where my powerful computers are. I only have an old, very old, laptop with me. Which supports neither OpenGL nor openFrameworks. Can only help with "theory" right now.

@madskjeldgaard Another approach would be to insert a geometry shader into the pipeline between the vector shader and the fragment shader. The geometry shader receives the two end points of the straight line. And creates 2 triangles. So that a long and small rectangle is formed along the line.

Input 1 line
+------+

Output 2 triangles
| ------+
| - +
| - +
| - +
| - +
|------+