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Sample source

Browse the full sample on GitHub: raytrace_tutorial/02_basic_nvvk

02 Basic Ray Tracing - Tutorial (Helper Version)

02 Basic ray tracing result (nvvk helper version)

This tutorial demonstrates the foundational ray tracing implementation by converting the raster foundation to use ray tracing pipelines. It introduces the core concepts of ray-based rendering with acceleration structures, ray generation, closest hit, and miss shaders. This serves as the essential foundation that all subsequent ray tracing tutorials build upon.

This version uses nvpro-core2 helper libraries (nvvk::AccelerationStructureHelper and nvvk::SBTGenerator) to simplify acceleration structure creation and shader binding table management. For a direct Vulkan implementation without helpers, see 02_basic.

Key Features

  • Ray Tracing Pipeline: Multi-stage shader pipeline for ray-based rendering
  • Acceleration Structures: BLAS and TLAS for efficient ray-geometry intersection
  • Shader Binding Table: Management system for ray tracing shaders
  • Ray Generation: Camera ray creation and dispatch
  • Closest Hit Shading: Material shading at ray intersection points
  • Miss Shader: Background/sky rendering for rays that miss geometry

Architecture Overview

This implementation transforms the raster foundation by replacing the traditional graphics pipeline with a ray tracing pipeline. Instead of rasterizing triangles, rays are generated from the camera and traced through the scene using acceleration structures for efficient intersection testing.

Pipeline Type: Ray tracing pipeline vs graphics pipeline
Shader Types: Ray generation, closest hit, miss shaders
Geometry Handling: Acceleration structures (BLAS/TLAS)
Rendering Method: vkCmdTraceRaysKHR vs vkCmdDrawIndexed

Key Components

  • Acceleration Structures: BLAS for geometry, TLAS for instances
  • Shader Binding Table: Ray tracing shader management
  • Ray Tracing Pipeline: Multi-stage shader pipeline
  • Descriptor Bindings: TLAS and output image bindings

Helper Libraries Used

This implementation leverages nvpro-core2 helper libraries for simplified development:

nvvk::AccelerationStructureHelper

  • Automatic scratch buffer management: Handles temporary memory allocation and cleanup
  • Batch building: Efficiently builds multiple acceleration structures in parallel
  • Memory optimization: Reuses scratch buffers and optimizes memory layout
  • Simplified API: Reduces boilerplate code for BLAS and TLAS creation

nvvk::SBTGenerator

  • Automatic alignment calculation: Handles complex alignment requirements
  • Shader handle management: Retrieves and organizes shader group handles
  • Buffer population: Automatically populates SBT buffer with correct data
  • Region management: Provides easy access to SBT regions for ray tracing

Benefits of using helpers: - Reduced code complexity and maintenance - Better performance through optimized memory management - Fewer opportunities for alignment and memory errors - Focus on rendering algorithms rather than infrastructure

Shader Structure

Ray Generation Shader

[shader("raygeneration")]
void rgenMain()
{
    // Generate camera rays and trace them
    RayDesc ray;
    ray.Origin = cameraPosition;
    ray.Direction = normalize(rayDirection);
    TraceRay(topLevelAS, rayFlags, 0xff, 0, 0, 0, ray, payload);
}

Closest Hit Shader

[shader("closesthit")]
void rchitMain(inout HitPayload payload, in BuiltInTriangleIntersectionAttributes attr)
{
    // Basic material shading at intersection point
    payload.color = float3(1, 0, 0); // Simple red color
}

Miss Shader

[shader("miss")]
void rmissMain(inout HitPayload payload)
{
    // Sky/background color for rays that miss geometry
    payload.color = float3(1, 1, 1); // White background
}

Key Differences from Foundation

  1. Pipeline Type: Graphics pipeline → Ray tracing pipeline
  2. Shader Types: Vertex/Fragment → Ray generation/Closest hit/Miss
  3. Geometry: Vertex buffers → Acceleration structures
  4. Rendering: vkCmdDrawIndexed → vkCmdTraceRaysKHR
  5. Descriptors: Added TLAS and output image bindings
  6. Memory: Added SBT buffer for shader binding table

Implementation Highlights

This basic implementation enables: - Global Illumination: Rays can bounce and gather lighting from any direction - Accurate Reflections: Perfect mirror-like surfaces without approximation - Complex Lighting: Multiple light sources with proper shadow casting - Future Extensions: Foundation for advanced effects like transparency, motion blur, and callable shaders

Next Steps

For step-by-step conversion guide, see rt_tutorial

This basic implementation can be extended with: - 03_any_hit - for transparency and alpha testing - 04_jitter_camera - for temporal anti-aliasing - 05_shadow_miss - for efficient shadow testing - 06_reflection - for mirror-like surfaces and global illumination - 07_multi_closest_hit - for different materials per object - 09_motion_blur - with animated acceleration structures

For detailed information about the core ray tracing components: