This is something really strange,
If you open this website https://www.windy.com/?18.177,-67.577,4 with the WebKitGTK+ minibrowser you see it ok (like on other browsers) if you are running Wayland. But under X11 the wind lines look all wrong (always straight lines that don't make any sense)
See the attached image, on the left the MB on X11, on the right the MB on Weston on X11. Both built on the same revision: r221865
Created attachment 320452 [details]
on the left minibrowser on x11, on the right minibrowser on weston/wayland
Maybe it's GLX issue, could you try with X11 but using EGL?
What happens here is that the page uses WebGL, and it's using a texture with GL_LUMINANCE_ALPHA format. This format is deprecated when using an OpenGL core profile. When using glx we use a 3.2 core profile if available, so the format is wrong and the rendering is buggy. But when using EGL we don't request an OpenGL version, so we get an older version that still supports the format and the rendering works.
The fix for this is easy, just backing GL_LUMINANCE_ALPHA with the appropriate format for a core profile. But at some point we should look into requesting a core profile for EGL as well. From what I read, in order to do this we require EGL 1.5 or EGL 1.4 and the extension EGL_KHR_create_context. I'll open a new bug to handle this.
Created attachment 324663 [details]
Comment on attachment 324663 [details]
Clearing flags on attachment: 324663
Committed r223887: <https://trac.webkit.org/changeset/223887>
All reviewed patches have been landed. Closing bug.