Recent searches
Search options
So I'm trying to port this OpenGL wireframe renderer from a 2008 paper to bevy. The code is simple. It is a legit one pager. See the repo for code and paper.
It has caused me a major hiccup though because it uses a geometry shader, which are not supported by bevy and to be avoided in general. The geometry shader does the simplest thing too: It adds a vector to each vertex. That's it. Well, heck, I should be able to do that. 1/
2/ Shaders I'm good with. I like WGSL. Pipelines and render nodes I am confused by. Anyway, I've been toying with this project off-and-on. I've tried to read bevy related examples and internal implementations; it's been lots of reading, not a lot coding. My mind has been plagued by lots of, "I don't know what I'm doing.” It's been a while since I've felt so out of my depth, kind of exciting—in the bad way.
3/ Despite making bevy_wireframe repo, my most fruitful work has been just tinkering with the bevy examples directly in its repo on a little branch I made.
I've been mucking with mesh2d_manual, which seems like it has the right bones for what I want to do. My ultimate aim is use a compute shader to read the mesh, transform it, compute the new "dist” vector for each vertex, which in the fragment shader is the distance to the triangle edges. Write that to a buffer.
https://github.com/shanecelis/bevy/tree/wireframe-scratchpad
4/ For my first pass, I inserted the new vector data directly to the mesh computed on the CPU. And it works!
For 2d if it's not otherwise distorted, this would be sufficient but of course I'd like for it to be general and work on 3d.
For my second pass, I created a GPU buffer but I still computed its initial data on the CPU. Same image.
My next step is to move the computation from the CPU to the GPU with a compute shader.
5/ Following that, I need to setup the buffers on a per mesh instance basis. Right now there's just one GPU buffer that's setup very ad hoc.
The above all looks much more cogent than it's felt. It's been a lot of banging my head against the screen and wondering if anything is seeping in. The next steps are much more fuzzy.
I need to mark objects that want a wireframe with settings.
It feels like I'd want to have a render node that produces a "dist" buffer for any given mesh but who knows?
6/ ME, talking to myself after many failed attempts: So I should get all but one.
ME: Awww yeaaahhh, boys!
That's held together string, glue, and some compute shaders.
7/ Oh, compute shader node, why won't you run?
[Searches bevy's discord for ViewNode.] Ooo, this looks promising.
9/ Feeling pretty chuffed, I then tried to draw a simple Circle shape and it went poorly.
10/ I posted on the help channel for the bevy discord with a minimally changed example. This should be a red circle, but it’s only half a circle and it's made of spikes.
The problem? I hadn't specified that the vertex layout had normals and UVs in them. After that my minimal example did the right thing.
11/ My pipeline could not draw the star and the circle at the same time though because my vertex layout was hard coded. But after some refactoring, we’re finally in a kind of normal place. Next I'd like to add some dashed lines, color choice, and then create the 3d version. The compute shader isn't actually doing this in screen space yet either (just model space right now), so yeah, lots left to do for this “little" project.
12/ Dashed me brain to pieces for uniform dash width.
This is coming directly out of the bevy_wireframe repo with the mesh2d_manual example. https://github.com/shanecelis/bevy_wireframe
#bevyengine #shaders
