Abstract:

This live stream documents Aerno's return to programming on the Hazel game engine, focusing on the "Renderer 2025" project. This major refactoring effort involves migrating Hazel's rendering backend from a direct Vulkan implementation to utilize Nvidia's NVRHI library, which serves as an abstraction layer for various graphics APIs (Vulkan, DirectX11, DirectX12). The stream meticulously details the process of porting core rendering components—including Index Buffers, Vertex Buffers, Pipelines, Images, FrameBuffers, Textures, and Compute Pipelines—by adapting Hazel's existing API to NVRHI's paradigms. Key challenges tackled include managing different resource creation patterns, handling API-specific nuances like framebuffer load/store operations, and addressing extensive compilation errors. A significant amount of Vulkan-specific code is deleted as part of this transition. Future major tasks identified include rewriting the ImGui renderer and overhauling the descriptor set management system to align with NVRHI. The overarching goal of this work is to modernize Hazel's renderer and pave the way for a free, binary release of the engine (Hazel 1.0).

Hazel Engine - Renderer 2025 Refactor with NVRHI (Live Stream)

• 0:00 Introduction & Project Scope: Aerno returns to streaming after a long break, focusing on the "Renderer 2025" project for the Hazel game engine. This is a major refactor on the renderer_2025 branch, aiming to modernize the renderer and enable Hazel's eventual free public release (Hazel 1.0).
• 0:44 NVRHI Integration: The core of the refactor is transitioning Hazel's rendering abstraction to Nvidia's NVRHI library. NVRHI abstracts Vulkan, DirectX11, and DirectX12, allowing Hazel to remove its direct Vulkan implementation and leverage NVRHI's cross-API capabilities.
• 1:21 Roadmap & Shader Strategy: Aerno consults the hazelengine.com/roadmap outlining NVRHI support for Vulkan and D3D12. This requires shader cross-compilation (SPIR-V for Vulkan, DXIL/DXBC for DX). He considers switching from GLSL to HLSL for easier cross-API shader management, despite his preference for GLSL.
• 2:20 Initial Porting & Error Handling: The session begins with a staggering 1658 compilation errors. Aerno methodically addresses errors by disabling problematic features (like GLSL live compiling) and focusing on one file at a time, starting with IndexBuffer.cpp and VertexBuffer.cpp.
• 2:56 Private Constructor Refactor: A key change involves making formerly private constructors public, with static Create functions becoming the preferred way to instantiate objects. This simplifies the API for users, as NVRHI handles the backend-specific object creation.
• 4:08 Pipeline Rework: The Pipeline implementation is migrated from its Vulkan-specific class (VulkanPipeline.cpp) to the base Pipeline.h/cpp as it now uses NVRHI. The old VulkanPipeline files are then deleted, marking significant progress.
• 4:44 Image & ImageView Migration: Aerno begins porting Image.cpp and Image2D.cpp from VulkanImage.cpp, adapting them to NVRHI's TextureSubresourceSet for image views. The VulkanImage files are subsequently deleted.
• 7:00 FrameBuffer Challenges: Rewriting FrameBuffer.cpp proves challenging. Hazel's FrameBufferSpecification combines color and depth attachments, while NVRHI's NVRHI::FrameBufferDescription separates them. A major "to-do" is identified regarding framebuffer load/store operations (clear vs. load), as NVRHI's default behavior needs explicit management.
• 7:59 Texture & TextureCube Porting: Texture.cpp and TextureCube.cpp are ported, involving NVRHI::TextureDescription and NVRHI::SamplerDesc for texture creation. Acknowledging a legacy design, each texture currently creates its own sampler, a practice that might be revisited. The VulkanTexture files are deleted.
• 2:40:55 ImGui Renderer Rewrite (Future Work): Aerno notes that the existing ImGui renderer (VulkanImGui.cpp) is deeply tied to Vulkan and will require a complete rewrite for NVRHI, presenting a significant upcoming challenge.
• 2:50:01 Descriptor Set Management Overhaul (Future Work): The current DescriptorSetManager is heavily Vulkan-specific. A complete redesign is needed to align with NVRHI's BindingSetDescription and BindingSet concepts for resource management.
• 2:53:51 Compute Pipeline Integration: Aerno starts porting ComputePipeline.cpp, mapping it to NVRHI::ComputePipelineDescription and ComputeState for dispatch. He notes NVRHI offers unexpected granularity and control for compute shaders.
• 3:06:16 Stream Conclusion: Aerno wraps up the stream, having reduced compile errors significantly. He acknowledges the substantial work remaining, particularly the ImGui renderer and descriptor management, and expresses interest in trying Rust programming in the future.