Fix gizmo on top material option having no effect

[stevenjt]

This fixes #44077

I found that the get_material function in EditorNode3DGizmoPlugin is changing the gizmo materials directly to add and remove the disable depth test flag to enable/disable them for the 'x-ray' visibility state before returning them. This is causing the original state of the disable depth test flag to be lost so materials that were created with the on_top parameter are never returned with the disable depth test flag enabled when in the regular 'visible' visibility state.

To fix this I have updated get_material to change the disable depth test flag on duplicate versions of the gizmo
materials when the gizmo is set to use the 'x-ray' / ON_TOP visibility state if the flag is not already set or otherwise return the stored materials without change.

(Since StandardMaterial3D is RefCounted these duplicates should be freed automatically when later unreferenced when the gizmo is redrawn.)

[Calinou]

Tested locally (rebased on top of master b2f425f), it works as expected on #44077 (comment). Code looks good to me.

Toggling x-ray visibility on default gizmos still works.

[akien-mga]

Thanks! And congrats for your first merged Godot contribution 🎉

[donn-xx]

Trying this in my plugin: create_material("small_cursor_shape", Color.RED, false, true)
Not sure what it's meant to do, but my expectation is to see the red (sphere) through the geometry in the way. However it's hidden.

Zylann's workaround still better:

func create_on_top_material(name: String, color := Color.WHITE,
		bmode := StandardMaterial3D.BLEND_MODE_ADD):
	var material := StandardMaterial3D.new()
	material.set_blend_mode(bmode)
	material.set_shading_mode(StandardMaterial3D.SHADING_MODE_PER_VERTEX)
	material.set_flag(StandardMaterial3D.FLAG_DISABLE_DEPTH_TEST, true)
	material.set_albedo(color)
	material.render_priority = 100
	add_material(name, material)

ETA:
The func create_icon_material("test", iconref, true) is doing the same thing, the icon not visible through the other things in the scene.
ETA:
In the case of the icon_material, there is some more weirdness. My texture is from an svg. Sometimes the billboard drawn by add_unscaled_billboard does show through, other times not. Also, when the gizmo is selected, the texture gets an ugly background (it was alpha before).

Selected gizmo. The background has gone awry.

Unselected gizmo.

Godot v4.4.dev (61598c5) - Ubuntu 22.04.4 LTS 22.04 - X11 - Vulkan (Forward+) - dedicated NVIDIA GeForce RTX 2060 (nvidia; 535.183.01) - Intel(R) Core(TM) i5-9400F CPU @ 2.90GHz (6 Threads)

[stevenjt]

@donn-xx in your create_material example does it work when the node using the gizmo is selected? Gizmos have different material instances created for selected and unselected states. The on top effect is only applied to the selected material instance:

godot/editor/plugins/node_3d_editor_gizmos.cpp

Line 928 in 61598c5

if (p_on_top && selected) {

[donn-xx]

he selected material instanc
Selected and unselected. The billboard simply changes (in some way) how it appears.

How do we setup the selected and unselected materials?

Also, imo, I need the "icon material" (at least) to be visible always, so that it's visible in the scene (in the editor). It would be great to be able to select the node by clicking on the billboard/icon too. (Otherwise, why bother with it all? May as well select the node in the tree.)