Line rendering example

[lobneroO]

Is there an example for line rendering somewhere? I couldn't find any sample code so far, but rendering lines would be helpful in contexts like ray tracer debugging or graph creation.

I have found the documentation regarding some of the necessary objects, but it is not clear to me yet, how to set this up. E.g. the rasterization for lines needs to be set up as pNext pointer of a pipeline rasterization, but does that require the pipeline rasterization to be set up in a specific way?

[asuessenbach]

I assume, you're not asking for vk::PolygonMode::eLine?
That is, would you elaborate a bit more in detail what you're looking for?

[lobneroO]

I am trying to render a line(/vector) in 3D space. Not a wireframe, i.e. not lines of triangles, but of two points. In my case, I just want to debug rays in a ray tracer and visualizing a few may be a great help. It's obviously not as trivial as just connecting the start and end of every ray, but to get anything going at all, I need to render a line between to points in 3D space and have a depth test enabled.

An example of the effect would be the "draw debug line" that Unreal Engine offers:
https://youtu.be/ts4p1Sh52ek?feature=shared&t=61
The guy created a line that is fixed in 3D space through two world positions and if he moves about, the line stays at its world position (of course it's redrawn every frame for this to work, I'm not expecting miracles :-) ).

[asuessenbach]

Would vk::PrimitiveTopology::eLineList in the vk::PipelineInputAssemblyStateCreateInfo (or vk::CommandBuffer::setPrimitiveTopology() when corresponding dynamic state is set) and vk::PipelineRasterizationStateCreateInfo::lineWidth (or vk::CommandBuffer::setLineWidth() when the corresponding dynamic state is set) do what you need?

[lobneroO]

I actually have my input assembly set up with that primitive topology, but I'm not yet at a point of rendering. If that is sufficient to render lines, what is the special line rasterizer VkPipelineRasterizationLineStateCreateInfoEXT for? I had been trying to integrate this into the pipeline rasterizer's pNext chain.

If your suggestion is sufficient, that's basically the example I had been asking for, I guess. Hard to say, as I am just getting into this topic - but I couldn't see any example code (even outside of this repository) about simple line rendering.

[asuessenbach]

VkPipelineRasterizationLineStateCreateInfoEXT is part of the VK_KHR_line_rasterization extension:

This extension adds some line rasterization features that are commonly used in CAD applications and supported in other APIs like OpenGL. Bresenham-style line rasterization is supported, smooth rectangular lines (coverage to alpha) are supported, and stippled lines are supported for all three line rasterization modes.

That is, for simple line drawings, you don't need that. Only if you want to use more sophisticated line stippling and such, you need to go that route.

[asuessenbach]

Assuming, this question is answered...

[lobneroO]

Sorry for the delay. Finally got round to work on it and get the first results. The suggested solution works, and I do get a line on screen. I still think, it'd be neat to have an example (e.g. draw a histogram or something like that).
Either way, thank you for the help!

[asuessenbach]

Maybe you could file an issue requesting for such a sample on https://github.com/KhronosGroup/Vulkan-Samples.