This one is for the straight line (white with width 2.0 over a black with width 4.0) drawn when you use the gradient tool.
To test: Image editor, create / open an image, choose image paint mode and on the tool shelf: choose the Fill brush and enable "Use Gradient" for it. Then click and drag on the image.
From what I checked, calls to glLineWidth are not being removed yet, so I kept them.
Reviewers: dfelinto, Severin, merwin
Reviewed By: merwin
Tags: #bf_blender_2.8, #opengl_gfx
Maniphest Tasks: T49043
Differential Revision: https://developer.blender.org/D2312
12bce04b2f