There is still a transparency issue with setting ALPHA=1.0 in the shader script

[jianliang-li]

Tested versions

4.0.4, 4.2, 3.5

System information

macOS 14.4 (23E214) Godot 4.2, 4.0.4

Issue description

Setting ALPHA=1.0 in the shader script still has a transparent effect, just like setting the transparency of StandardMaterial3D to alpha or setting no depth test.
But if the rendering mode of the shadow script adds depth_draw-always, setting ALPHA=1.0 can display normally, but it cannot produce shadow effects.

Steps to reproduce

In the project I uploaded:
In the scene of node_3d_desk, the shader script has set ALPHA=1.0 and I do not want to see the tripod of the table.

Desk_normal has added StandardMaterial3D to the surfaceMaterialOverlay of Box024 without any changes.

Desk_alpha added StandardMaterial3D to the SurfaceMaterialOverrides of Box024 and changed transparency to alpha.

Desk_no_depth_test has been added to StandardMaterial3D and transparency has been changed to no_depth_test in the surface MaterialOverrides of Box 024.

Desk_shaded_alpha added ShaderMaterial in the surfaceMaterialOverride of Box024, with only ALPHA=1.0 set in the script.

In the scene of node_3d_sofa, there is also a similar problem. This problem occurs whenever the mesh has an irregular shape.

How can I set ALPHA=1.0 in the shader without expecting transparency or no_depth_test effects, and still display shadows normally.

When I add render_mode depth_draw_always in the shader script, it can display normally, but it cannot display shadows properly. If the following image is displayed:
Shadow display in normal mode:

Display shadows after setting ALPHA=1.0 and adding render_mode depth_draw_always:

Minimal reproduction project (MRP)

Test0520.zip

[Calinou]

This is expected, as setting ALPHA anywhere in the shader will force the material to go through the transparent pipeline. This is the case even if you only use ALPHA = 1.0.

I don't think we should have a special case for ALPHA = 1.0 not making the material go through the transparent pipeline. Could you describe why you want to write to ALPHA in the first place? Perhaps you can achieve the desired effect another way.

[Khasehemwy]

I had a similar problem, when using depth_draw_always, ALPHA=0.9 or less resulted in depth not being written, but ALPHA=0.99 did.
(engine version 4.3.dev)

(a sphere in the scene, screen shows the view depth)

[clayjohn]

@Khasehemwy what you are seeing is a different issue from the OP.

In your case you are seeing a few different things:

1. Because depth_prepass_alpha is being used, the object is rendered in the depth prepass. However, the depth prepass will only write out the depth for objects that have an alpha higher than 0.99. Accordingly, nothing is written in the depth prepass.
2. When you read from the depth texture, you are actually reading a copy of the depth texture that was copied right after doing the depth prepass. Therefore, only objects caught by the depth prepass are included
3. Because depth_draw_always is enabled, the depth is written during the transparent pass. You don't see the results in the depth texture, because the depth texture was copied before the transparent pass

[Khasehemwy]

@clayjohn Thank you! I found the changes needed to make the depth pre pass work for transparent objects. But does that mean there is no way to get the depth of a transparent object by depth texture in official version?

[clayjohn]

@clayjohn Thank you! I found the changes needed to make the depth pre pass work for transparent objects. But does that mean there is no way to get the depth of a transparent object by depth texture in official version?

When using hint_depth_texture that is correct. You can however get the depth texture after rendering transparent objects using a CompositorEffect in 4.3

[Datoh]

This is expected, as setting ALPHA anywhere in the shader will force the material to go through the transparent pipeline. This is the case even if you only use ALPHA = 1.0.

I don't think we should have a special case for ALPHA = 1.0 not making the material go through the transparent pipeline. Could you describe why you want to write to ALPHA in the first place? Perhaps you can achieve the desired effect another way.

Hi,
I have the same issue, I'm developing a multiplayer golf game where each player has a ball.
No collision is possible between balls.
So when the player's ball is too near another ball, I would like to fade the other ball according to the distance to the player ball. It is very similiar to the way trackmania deals with display of others cars (eg: https://www.reddit.com/r/TrackMania/comments/1ejmn1y/just_started_playing_did_i_do_good_and_how_can_i/)
Acoording to the way Alpha is working on Godot shaders, my solution could be to duplicate meshes, one with alpha one without. Any other solution?

[eddieataberk]

Having trouble with this too. I am setting opacity of the objects inbetween the character and the camera to 0.5 however in that case lighter objects are still visible while darker objects are not. i also wanto make it so that only top half of the objects gets faded. however even if i add if(ALPHA < 1.0){} whole object gets transparent even if transparency is set to 0.0 we need a solution for this.

[Nagasadri]

My use case is a 3D UV sphere mesh with a vertex displacement shader, used for a smoke VFX.
The bottom and top of the sphere (where the UV seams are) shows front faces through its sides because of their different displacement, even at 1.0 alpha.

I need to use alpha to make it fade out near the end of its animation, but those faces always show through, before the fade ever starts. The problem doesn't occur when the alpha input is left blank, but this prevents ever fading out the mesh...

Swapping meshes would be a pretty cumbersome solution, especially if I use this particle from many different sources with different sets of parameters.