CameraHelper needs 2 frames to update itself

[makc]

https://jsfiddle.net/et67ogua/ comment line 49 (requestAnimationFrame). the result:

the expected look is still this:

[makc]

ok, maybe this is actually because cameras updateProjectionMatrix does not work for light.shadow.camera )

[Mugen87]

The problem is that the internal matrices of the shadow camera are only updated when the shadow map is rendered, see:

three.js/src/renderers/webgl/WebGLShadowMap.js

Line 184 in d23b071

shadow.updateMatrices( light, vp );

Hence, the helper is so called "frame late". This is also true for other helpers, see #14801.

[Mugen87]

I've recently needed a camera helper that renders the shadow camera frustum in the first frame correctly. I've ended up with a custom ShadowCameraHelper class that internally uses CameraHelper. Here is the above live example with the new class: https://jsfiddle.net/vLq0racx/2/

Initially, I've tried to derive a class from CameraHelper but since the constructor directly calls update(), it's not possible to add additional properties that are used in an overwritten update() method. Although inheritance would be the more clean solution, the current design should also work.

[Mugen87]

To sum up: An appropriate fix can't be implemented without API changes to CameraHelper because the module needs a reference to the shadow camera's light to compute the correct (up-to-date) matrices. However, coupling a light with a plain camera helper sounds strange and only makes sense in context of shadow cameras. So if this issue comes up again at some point, I would rather suggest to add ShadowCameraHelper with the code from #17889 (comment). Given that this is a minor issue that is highly overlooked on application level, considering it as a Won't fix.