This was done while working on "ATOM-15728 Shader Hot Reload Fails in Debug Build", but it turned out these changes did not actually fix the issue (or any other known hot-reload issue). Still, these improvements are appropriate as they correct logical oversights.
ShaderVariant was not listening to asset reloads. It needs to know when the ShaderVariantAsset reload happens so it can reinitialize it's members as well as propagate reinitialization messages. I added a member for the ShaderAsset as the class needs this to reinitialize itself. So now the class listens for reloads of both the ShaderVariantAsset and the ShaderAsset.
Shader was not listening for ShaderAsset reinitialization events.
Updated the API for ShaderReloadNotificationBus's OnShaderVariantReinitialized to include the ShaderVariant which is the most relevant information (the other information wasn't really being used anyway).
ATOM-15728 Shader Hot Reload Fails in Debug Build
The main change was to add OnAssetReady handlers to each of the asset classes. See comments in ShaderAsset::OnAssetReady for a detailed explanation. In short, OnAssetReloaded gets missed while assets are being reloaded at the same time on multiple threads, but OnAssetReady is always called whenever connecting to the AssetBus because of its AssetConnectionPolicy.
The above change required the addition of a new AssetInitBus to call the PostLoadInit() functions. Because OnAssetReady connects to buses that are not mutex-protected, they have to be connected on the main thread. AssetInitBus::PostLoadInit is called every frame in RPISystem::SimulationTick. All Atom's asset handlers that need to do post-load initialization must connect to the AssetInitBus, and the asset will disconnect itself after initialization is complete.
We also need the Shader class to handle OnShaderAssetReinitialized to properly handle the shader reload.
With these changes I can click back and forth between "Blending On" and "Blending Off" many times (like 20 times) without issue.
This is specifically in support of:
ATOM-14613 Baseviewer MatertialHotReloadTest fails to change the color after turning blending on and off
ATOM-15728 Shader Hot Reload Fails in Debug Build
Chris Santora
alexpete