how to display wireframe in threejs

[ghost]

Hello
i want to display mesh with wireframe, but it seems not work, can you supply an demo material to me on how to display mesh with wireframe, thanks!

[ponchio]

Hi,
wireframe rendering is way more complicated than it looks.

Note: do we really want to use wireframe? Nexus is split in blocks using different resolution and swaps betwenn resolutions when data arrive, when you zoom in and out or even pan. This is hardly noticeable for full triangle rendering but in wireframe it would be a constant flickering.

Unfortunately the easy threejs approch of using WireframeGeometry doesn't work, nexus renders geometry behind threejs engine (for perfomance reasons).

Most common approaches:

1. render using gl.LINES: we need to create the line index from the triangle index (it's trivial), create an extra set of buffers holding the indexes. this is what WireframeGeometry is doing. Threejs would provide the shader.
   Main problem is that it's pretty slow especially since we don't want duplicated edges, and especially if you want to swap between wireframe and solid rendering.

2. use barycentric coordinates:
   we add an attribute which has (0,0) (1,0) (0,1) coords for each triangle
   we need to 'unindex' the vertices (space grows 3x!) (this is trivial but has the same problems as above)
   we need a custom shader

3. geometry shader, glPolygonMode, but we are in webgl2 and they are not available.

In summary: there are no good wireframe solutions for large models in webgl2, option 1 looks the most promising, but requires some effort.

I have made a commit where if you specify:

nexus_model.material.wireframe = true;
nexus_model.material.needsUpdate = true;

it simply replaces TRIANGLES with LINE_STRIP, you will be able to see the wireframe, but also wrong lines.
Due to the particular corto compression triangle sequence, the number of wrong line can be pretty small.

[ghost]

Many many thanks for the information.
As you said, after modifying according to your method, the wireframe of the mesh can be seen, but some triangles seem to be incorrect, is there any way for me to ensure the correctness of the mesh?
Best regards