Shadow Frustum Culling bug

[Eldarduil]

Is there an existing issue for this?

• I have searched the existing issues

Describe the bug

Shadows can only be visible from one direction and cannot be visible from another direction.

It seems like Shadow frustum orientation only locked to the directional light's rotation. or some values of the directional light has strange issue. Not sure exactly what is wrong, But my guess is, Directional Light's shadow bound gizmos are not big enough so since its targeting the scene camera it cut shorts on the opposite side of the light direction.

Shadows can be seen from very long distance:

Almost about same distance away but now the light is behind the camera:

ShadowFrustum03.mp4

Here I tried to explain the issue how I think it is happening. When the camera is looking away from the direction of the light, it only see the area that shadow casting boundary doesn't reaches. No matter how big number you put on your distance from layer's camera and shadows frustum size this issue still persist. I guess we need couple extra settings to fix this type of issue for rendering far shadows

as it can be seen on this example finding the perfect sweet spot is not easy
https://threejs.org/examples/webgl_shadowmap_csm

But if more options given for directional light, user can find the sweet spot for their game's need. Also without visualization of the light and shadows boundaries it might be hard setup, but personally it is always better to have all the options of the lights sources that threejs gives us.

Steps to reproduce

Example Project:
Shadow Frustum Test.zip

GDevelop platform

Desktop

GDevelop version

5.5.244

Platform info

OS Windows

Additional context

No response

[4ian]

The shadow area is indeed for now following the camera and oriented according to the light. I guess we could have a slightly more smart positioning by moving the area so that it's always "in front of the camera" (but not too much, otherwise things in front of the camera would lose their shadows... and you would also risk not seeing the shadows from huge objects behind you).

Do you have specific options from Three.js that you think should be exposed?

[Eldarduil]

I am not a professional programmer but from my tests with threejs directional light, shadow camera boundary size is important to define your shadow area.

As I tried to describe in my MsPaint sketch, I did put an arrow says "needs to be extended" that points the shadow camera far value If we can increase that value till it touches the ground object, we will be able to see shadows while the directional light is behind the camera.

In my sketch, light comes from at 45 angle. On ground level, Shadow covering area at the direction of the light, frustum size/2 and at the the other side we only have 10000 units, because the code only adds flat 10000 units and the square prism boundary of shadow camera cuts shorts to reach other side of the camera. Also since the directional light follows the camera on Z elevation, if the camera is higher than ground level we also lose that limited 10000 units of area too.

GDevelop/Extensions/3D/DirectionalLight.ts

Line 56 in 4d4b86a

this._light.shadow.camera.far = this._distanceFromCamera + 10000;

So even if we only have access to the Shadow camera far value, we can increase and decrease for our games needs. Shadow Camera right, left, top, bottom all of them changing all together is alright. But I believe it would be better to turn that flat 10000 units into a variable and add it to the advanced list so we can change it.

Also it would be good that be able to activate Camera helper for light shadow camera so we can see our shadow boundary.

It was a bit hard to explain the situation about "shadow camera far" by only text and English not being my first language made it a bit more difficult. But I believe my sketch clearly shows that shadow boundary are cuts short at some certain angles and 10000 units of margin might be not enough for every situation.

If it needs more explanation I can make some 3d animations to explain it more.