Hello!
I’m trying to find out how to detect if an object (like a TCastleScene or any TCastleTranform) is in field of vision of the viewport (TCastleViewport or its TCastleCamera).
How do I do that?
PS: Maybe this solution is already described in the documentation, examples or on the forum, but I didn’t find it, sorry in advance
See Castle Game Engine: CastleScene: Class TCastleScene
If you want a more powerful version that accounts for objects behind other objects, then see Castle Game Engine: CastleScene: Class TCastleScene
Looks like I misread the documentation, the first one is actually for something else…
After reading the description, I also thought that it should work. But maybe it is only for the described specific case.
¯\_(ツ)_/¯
The TCastleScene.WasVisible ( Castle Game Engine: CastleScene: Class TCastleScene ) is indeed the exact solution to this.
Other things determine how do we detect this visibility.
SceneFrustumCulling ( Castle Game Engine: CastleScene: Class TCastleScene ) matters, it should usually be true (whether you use WasVisible or not, it’s usually a good optimization). When this is true (default), it matters if objects is in frustum or not.Sudden addition 
So what if I want to determine the visibility of the area or point where the object should appear, but it hasn’t appeared yet? What can I do then?
If you only want to detect “visibility, according to whether it is in frustum” then you can check “frustum vs box / sphere” collision yourself using routines like
To get TFrustum, you can just look at MyViewport.Camera.Frustum. It’s automatically updated.
( To get “visibility, accounting for the fact that object may be obscured by another object” is harder – our Occlusion Culling | Manual | Castle Game Engine doesn’t expose facility to check arbitrary things (not yet in world) now. You’d have to use the respective OpenGL/OpenGLES/WebGL API directly. See how castleinternalocclusionculling.pas is implemented. )