I am getting a gray rectangle instead of the shader effect on 3.0:
The shader is the exact same as the blur effect on the examples repo (https://github.com/godotengine/godot-demo-projects/tree/master/2d/screen_space_shaders).
What am I missing? Looks like it's something really simple, as the demo works fine, while my project doesn't.
I can't even reproduce the issue. Care to share your project file?
edit: I'm guessing you don't have a placeholder texture setup in the TextureRect.
