# Refactor Turbo Renderer State Management to Use RxJS
### TL;DR
Refactored the TurboRenderer state management to use RxJS observables instead of direct state mutations, improving state transitions and reactivity.
### What changed?
- Replaced the public `state` property with a private `state$` BehaviorSubject in `ViewportTurboRendererExtension`
- Added proper state transition logging using RxJS operators
- Combined multiple event subscriptions using `merge` operator for better organization
- Improved state transition logic in the `refresh()` method
- Updated the `zooming$` and `panning$` signals in the Viewport
### Why make this change?
This refactoring improves the codebase by:
1. Using a more consistent reactive programming model with RxJS
2. Making state transitions more explicit and traceable
3. Reducing potential bugs from manual state management
4. Improving code organization by combining related event streams
5. Ensuring proper cleanup of resources when components are disposed
The change maintains the same functionality while making the code more maintainable and the state management more robust.
This PR refactored the turbo renderer architecture to support multiple block layout types.
- New base class `BlockLayoutPainter` and `BlockLayoutProvider` are introduced for writing extendable per-block layout querying and painting logic.
- Paragraph-specific lines are all moved into dedicated classes (`ParagraphLayoutProvider` and `ParagraphLayoutPainter`) under the `/variants/paragraph` dir.
- The `renderer-utils.ts` doesn't contain paragraph-specific logic now.
- The `text-utils.ts` is also now scoped for paragraph only.
- Worker messages are now strongly typed.
Upcoming PR should further implement the block registration system using extension API. The `variants` dir could still exist, since there will be similar rendering logic that can be reused among block types (i.e., between paragraph block and list block).
The `ViewportTurboRendererExtension` is now extracted from `@blocksuite/affine-shared` to `@blocksuite/affine-gfx-turbo-renderer` with minimal dependencies, mirroring the gfx text package in #10378.
