onBeforeRender called twice per render when passing a Mesh to the renderer.

[sjpt]

Description of the problem

When onBeforeRender is applied to a mesh, and that mesh is rendered directly (not via a scene), then the onBeforeRender callback is applied twice for each render call.

I appreciate that it is not standard practice to render a mesh directly, but there are cases where it is helpful to avoid (the very small) overheads in performance, and in code noise.

https://jsfiddle.net/sjpt/t664p2yn/

Three.js version

• [x ] Dev
• [x ] r116
• ...

Browser

• All of them
• Chrome
• Firefox
• Internet Explorer

OS

• All of them
• Windows
• macOS
• Linux
• Android
• iOS

Hardware Requirements (graphics card, VR Device, ...)

[Mugen87]

I think we have to change this line:

three.js/src/renderers/WebGLRenderer.js

Line 1174 in 452a9e9

scene.onBeforeRender( _this, scene, camera, renderTarget || _currentRenderTarget );

to

if( scene.isScene ) scene.onBeforeRender( _this, scene, camera, renderTarget || _currentRenderTarget ); 

and do the same thing for onAfterRender().

[WestLangley]

I think we have to change this line:

The renderer expects a Scene as the first argument, so we do not have to do anything.

If you do not think a Scene as the first argument is appropriate, then the first step is to change the API.

[Mugen87]

@mrdoob recently implemented a342f06 or 4cc880d so I think applying 3D objects directly to render() is valid.

[sjpt]

Associated comment. onBeforeRender() does not seem to get called when applied THREE.Group.

[Mugen87]

That's correct. It's only called for renderable 3D objects and scenes.

[sjpt]

Thanks. That should be clearer in the documentation.

Is there any reason not to apply it to groups?
I have group Group consisting of objects Wire and Shaded.
Both Wire and Shaded require the same preparatory work Prep().
I had assumed that setting Group.onBeforeRender=Prep would do that.

[Mugen87]

Is there any reason not to apply it to groups?

This was already discussed here: #11306

[sjpt]

That #11306 thread seems to say that it should work,
'mrdoob added this to the rXX milestone on 9 Mar 2018'

Came up again in #14970 which was closed in favour of #11306, but #11306 still isn't resolved.