Glitch in shader when using screen_texture and Compatibility mode: pink gridded lines

[fguillen]

Godot version

4.1.1.stable

System information

MacOS - Ventura 13.1 - Godot 4.1.1.stable

Issue description

When in a shader I use screen_texture:

uniform sampler2D screen_texture : hint_screen_texture, repeat_disable, filter_nearest;

and Compatibility mode. In many cases, a gridded pink lines appear:

In Forward+ mode:

In Mobile mode:

In Compatibility mode:

Steps to reproduce

Add this shader to a ColorRect in an independent CanvasLayer:

shader_type canvas_item;

uniform int amount = 40;
uniform sampler2D screen_texture : hint_screen_texture, repeat_disable, filter_nearest;

void fragment()
{
    vec2 grid_uv = round(SCREEN_UV * float(amount)) / float(amount);
    vec4 text = texture(screen_texture, grid_uv);
    COLOR = text;
}

Minimal reproduction project

TestingShaderGlitch.zip

[TZer0]

Also applies to v4.1.3.stable.mono.official [f06b6836a] (only compatibility mode, Forward works fine)

This is a very strange bug as it stops happening in the scene view in the editor if you turn off filter_nearest for a moment and then turn it back on. The bug is always visible in the material view.

[pirey0]

As a workaround: Using vec4 text = textureLod(screen_texture, grid_uv ,0.0) instead of vec4 text = texture(screen_texture, grid_uv) fixes the issue for me on v4.2.2

[clayjohn]

I can only reproduce this in 4.1.4 (I tested 4.3, 4.2.2, 4.2.1, 4.2.0, and 4.1.1)

Given the nature of the issue though, I'm not convinced that it is necessarily fixed. I have a feeling that https://github.com/godotengine/godot/pull/96502 may fix it though