Why doesn't my ParticleProcessMaterial uniform change?

You're calling set_shader_parameter on the asset, not the instance. Each GPUParticles2D has its own instance via .process_material; modify that.

Custom shader on process material?

ParticleProcessMaterial accepts a custom Shader resource via process_material's shader property. Uniforms exposed via set_shader_parameter.

Fix: Godot ParticleProcessMaterial Uniform Stays Default

Q: Per-emitter variation?

Duplicate the process_material with .duplicate() before assigning to a particles node. Each gets independent uniforms.

Quick answer: Modify node.process_material instance, not the asset. Use .duplicate() for per-emitter variation.

Set custom uniform on the asset; all emitters change. Or modify per-emitter; only one updates because they shared the asset.

The Fix

# Per-emitter uniform
@onready var p: GPUParticles2D = $Emitter

func _ready():
    var mat = p.process_material.duplicate()
    p.process_material = mat
    mat.set_shader_parameter("wind_speed", 5.0)

Duplicate creates a unique material instance. set_shader_parameter then targets only this emitter.

Verifying

Set uniform per-emitter. Each one’s wind speed differs. Without duplicate: all share asset.

“Duplicate. Per-instance uniforms.”

Related Issues

For shader uniform array, see array. For shader instance uniform, see instance uniform.

Duplicate. Set per instance.