How can I use the shader's built-in variables to store adjacent vertices

ning_xue

How can I use the shader's built-in variables to store adjacent vertices, I tried using arraymesh's NORMAL and TANGENT, but they are automatically normalized in the vertex shader, so if I want to store the true values of adjacent vertices and use in shader, how to do?

cybereality

So, you cannot access other vertices from a vertex shader. You only have access to one vertex at a time, since there can be thousands of verts processing in parallel and it would be too confusing or slow to access others due to race conditions. However, you can store varying data in the adjacent vertices and access that in a fragment shader. Look into barycentric coordinates, you might not find anything specific to Godot, but the general concepts for OpenGL or any other engine should apply.

ning_xue

@cybereality said: So, you cannot access other vertices from a vertex shader. You only have access to one vertex at a time, since there can be thousands of verts processing in parallel and it would be too confusing or slow to access others due to race conditions. However, you can store varying data in the adjacent vertices and access that in a fragment shader. Look into barycentric coordinates, you might not find anything specific to Godot, but the general concepts for OpenGL or any other engine should apply.

Thank you for your answer.I know that only one vertex can be accessed at a time in the vertex shader. I mean, when constructing the arrymesh, store the adjacent vertices in ARRAY_TANGENT or ARRAY_NORMAL. That way I can get the current vertex's neighbors via NOAML and TANGENT in the vertex shader. The problem now is that the data obtained through NOAML and TANGENT seems to be normalized, not raw. Is there any other way to store them to avoid them being automatically normalized?

cybereality

Well you have other slots for data. For example, you can use the vertex color and that will get your 3 extra floats (for example, to store a raw normal). You will have to look at the documentation as to what parameters are available on a vertex, and which ones you can replace or reuse for something else.

cybereality

But what are you trying to accomplish? Maybe there is an easier way.

ning_xue

In order to implement lines with custom widths in 3D space. To calculate the direction of the vertex offset, you need to know the two adjacent points. At the same time, in order to keep the width from changing with the viewing angle, you need to update the direction of the offset in real time, so I think it is necessary to calculate the offset direction in the shader. This It is also necessary to pass adjacent points to the shader. I've also tried storing vertex data to vertex colors, but I get values between 0 and 1 in the shader. Thank you for your answer, I will try other data slots or other methods. Maybe this method is really stupid.

cybereality

Yeah, I did this with barycentric coordinates. I'm not sure I saved the code, it might have been on my old computer which is no longer around. But I based the math on this tutorial, it was not that hard to port to Godot. https://catlikecoding.com/unity/tutorials/advanced-rendering/flat-and-wireframe-shading/

cybereality

So, I found the project on a backup. It's a mess and was just me testing stuff but maybe it will give you some ideas. You can show/hide the objects on the left, they are using different rendering methods.