Render an SCNGeometry as a wireframe

Question

I'm using SceneKit on iOS and I have a geometry I want to render as a wireframe. So basically I want to draw only the lines, so no textures.

I figured out that I could use the shaderModifiers property of the used SCNMaterial to accomplish this. Example of a shader modifier:

material.shaderModifiers = [
    SCNShaderModifierEntryPointFragment: "_output.color.rgb = vec3(1.0) - _output.color.rgb;"
]

This example apparently simply inverts the output colors. I know nothing about this 'GLSL' language I have to use for the shader fragment.

Can anybody tell me what code I should use as the shader fragment to only draw near the edges, to make the geometry look like a wireframe?

Or maybe there is a whole other approach to render a geometry as a wireframe. I would love to hear it.

Answer 1

Try setting the material fillMode to .lines (iOS 11+, and macOS 10.13+):

sphereNode.geometry?.firstMaterial?.fillMode = .lines

Answer 2

Now it is possible (at least in Cocoa) with:

gameView.debugOptions.insert(SCNDebugOptions.showWireframe)

or you can do it interactively if enabling the statistics with:

gameView.showsStatistics = true

(gameView is an instance of SCNView)