Vertex Shader Utilizing INV_VIEW_MATRIX not rendering shadows

[svenar-nl]

Tested versions

• Reproducible in: 4.3-dev6, 4.2.2, 4.0-stable, 3.6-beta4

System information

Godot v4.2.2.stable - Ubuntu 23.10 23.10 - X11 - Vulkan (Forward+) - dedicated NVIDIA GeForce RTX 2070 SUPER (nvidia; 545.29.06) - AMD Ryzen 7 3700X 8-Core Processor (16 Threads)

Issue description

Issue Description:
Creating a vertex bending shader using INV_VIEW_MATRIX produces no shadows wile using a different value (for example TIME) does produce a shadow.

Expected Behavior:
Shadows should be rendered accurately when utilizing the INV_VIEW_MATRIX in the vertex shader, similar to how they are rendered when using values like TIME.

Shader objects left (image):

void vertex() {
	VERTEX.y -= pow(length(INV_VIEW_MATRIX[3].zyz - VERTEX.zyz) / 20.0, 4);
}

Shader objects right (image):

void vertex() {
	VERTEX.y -= pow(length(sin(TIME) * 15.0 - VERTEX.zyz) / 20.0, 4);
}

---

This also exists in Godot 3 with the following shader:

shader_type spatial;

void vertex() {
	VERTEX.y -= pow(length(INV_CAMERA_MATRIX[3].zyz - VERTEX.zyz) / 20.0, 4);
}

Steps to reproduce

1. Create a MeshInstance3D with a plane mesh
2. Add the following shader to the MeshInstance3D

shader_type spatial;
render_mode world_vertex_coords;

void vertex() {
	VERTEX.y -= pow(length(INV_VIEW_MATRIX[3].zyz - VERTEX.zyz) / 20.0, 4);
}

3. Add a MeshInstance3D with a cube mesh and the exact same shader and place it above the other
4. Observe no shadows being casted from the cube onto the plane.

Minimal reproduction project (MRP)

• Godot 4.3-dev6: curveissue_4.3.zip
• Godot 4.2.2: CurveIssue.zip
• Godot 4.0-stable: CurveIssue_4.0.zip
• Godot 3.6-beta4: CruveIssue_3.6.4.zip

[svenar-nl]

Follow up

When manually supplying the shader with the position of the active camera the shadows are drawn correctly.
There is no visual difference between INV_VIEW_MATRIX and a manual camera position.

Left: Manual position
Right: INV_VIEW_MATRIX

Minimal reproduction project (MRP)

• Godot 4.2.2: CurveIssue.zip
  Renderer: Compatibility

[clayjohn]

In 4.3 we introduced a new built in variable to handle this situation: MAIN_CAM_INV_VIEW_MATRIX. Use that instead of INV_VIEW_MATRIX as INV_VIEW_MATRIX is the matrix used for rendering the object not the matrix from the camera in your scene.

There is an important distinction here because when rendering shadow maps the camera used is based on the position and orientation of the light.

[jsjtxietian]

Sounds like something that need better documentation?