Setting the emission property "_EmissiveColor " from script have different results when we use material.SetColor and materialPropertyBlock.SetColor (set using the material property block of the renderer).

Note that because the animation system uses property blocks, it have the same issues which make it hard to animate the emission property on materials.

Repro with 2021.2.0a13, HDRP 12

Repro steps:
- Create a new scene with a cube in it
- Create a new Unlit material with HDRP/Unlit shader
- Assign this material to the cube.
- Download the attached script and add it to the cube
- Toggle on and off the use material property block field.
- Observe that the intensity on the cube changes even though the script sets the same emission value in both cases.

Script:
using System.Collections;
using System.Collections.Generic;
using UnityEngine;

[ExecuteAlways]
public class SetEmission : MonoBehaviour
{
[ColorUsage(false, true)]
public Color emissionColor;

public bool useMaterialPropertyBlock = false;

new MeshRenderer renderer;

void Start()
{
renderer = GetComponent<MeshRenderer>();
}

void Update()
{
if (useMaterialPropertyBlock)
{
var p = new MaterialPropertyBlock();
p.SetColor("_EmissiveColor", emissionColor);
renderer.SetPropertyBlock(p);
}
else
{
var p = new MaterialPropertyBlock();
renderer.SetPropertyBlock(p);
renderer.sharedMaterial.SetColor("_EmissiveColor", emissionColor);
}
}
}