Why does my mesh disappear when partially off-screen after a vertex shader?

Godot culls based on the mesh AABB. If your shader displaces verts beyond that AABB, the visible silhouette extends past the cull box. Set MeshInstance3D.custom_aabb to enclose the displaced extent.

What's extra_cull_margin?

A simple uniform expansion of the AABB, easier than setting custom_aabb if you don't know the exact extent. Set on MeshInstance3D as a positive value (meters). Trade-off: simulation cost rises slightly.

Should I update custom_aabb each frame?

Only if displacement amount changes per frame. For a static wind shader with bounded amplitude, set custom_aabb once. For a dynamic blast wave, update each frame from script.

Fix: Godot 4 MeshInstance3D Custom AABB Wrong After Vertex Shader

Quick answer: Set MeshInstance3D.custom_aabb to an AABB that encloses the maximum displaced extent. Or use extra_cull_margin for a uniform expansion. Default culling uses mesh-bind-pose AABB.

A vertex shader displaces a flag mesh upward. Mesh visibly clips into view but the renderer culls it because the AABB still represents the un-displaced flag.

The Symptom

Mesh pops in/out as it edges into the camera frustum. The visible animated extent extends beyond the bounding box.

The Fix

extends MeshInstance3D

func _ready() -> void:
    # Manually expanded AABB to include max displacement
    custom_aabb = AABB(Vector3(-2, -1, -2), Vector3(4, 3, 4))

The AABB is in local space. Expand to cover whatever your vertex shader does at peak amplitude.

extra_cull_margin Alternative

extra_cull_margin = 2.0   # meters

Uniform expansion. Easier; less precise. Cost: more meshes pass culling each frame because the box is bigger.

Skinned Mesh Caveat

For SkinnedMeshes (animated), Godot 4 has its own handling but vertex shader displacement on top still requires custom_aabb. Combine.

Verifying

Walk the camera so the displaced mesh edges into and out of the frustum. With proper custom_aabb, the mesh stays visible until the AABB fully exits. Without, pops.

“Custom AABB or extra_cull_margin. Displaced mesh stays on-screen.”

Related Issues

For shader uniform runtime, see shader uniform. For shader uniform array, see uniform array.

Tell the renderer the real bounds.