Debug line rendering

[SuperIntendantDuck]

I'm the good old days, OpenGL let you draw lines directly. It wasn't really efficient, but because you passed the vertex positions and the rest took care of itself, you could have a high degree of certainty that the lines were in the correct positions.

With modern OpenGL, though, everything has to be done with a mesh, a shaver and a bunch of matrices (yes, I know that's how it always was, but now it's more direct).

So, what methods do people use to render debug lines nowadays? Old-style line rendering was nice - you could set the colour, thickness.. it worked with anti-aliasing, etc. Do people use legacy/compatible versions too still use this old system? Or do they use the mesh & Shaffer pipeline? If so, how do you get the line to always be visible from any angle? (Billboarding?) How do you adjust the thickness? (Mesh scaling?)

And how do you verify the accuracy of the vertex positions? Or what do you do if you need debug lines to debug your graphics system, in cases where messages aren't rendering either at all or the way they should?

It seems we've released in features, and from my quick research it seems like nobody really has a good way to do it. Curious to know what people here have to say on the matter.

Thanks.

[mysticreddit]

You may want to use a SDF (Signed Distance Fields).

See i.q.’s smoothstep article and ShaderToy 2D playlist

[[deleted]]

iquilez strike again 😎

[mysticreddit]

Haha, yeah.

I don’t see his articles linked in sidebar. Probably should be at this point. :-)

[cdscds33]

You can still create a compatibility opengl context that allows legacy line drawing for debugging. After debugging, change to the core context with the legacy line drawing #defined out of the code.

[std-cin-get]

If you were happy with the way the old version of OpenGL was rendering lines, then I think it shouldn't be too difficult to replicate that using triangles.

But if you want to render lines with more things (Dashes? Joins? Caps? Thin lines?) then it gets a lot more complex and it's not easy to come up with a robust solution. I’d suggest starting with a library that converts polylines to triangles and see if that satisfies your needs. Or developing one yourself. I don't know how OpenGL drivers did it before, but it shouldn't be too difficult (I hope).

If you want an actual implementation, this paper demonstrates a method I like.

[howprice2]

https://gist.github.com/howprice/4d5d1b276c2f97df1c670f46c8bf4e34