02_basic

02 Basic Ray Tracing - Tutorial

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.

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

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

Related Documentation

For detailed information about the core ray tracing components:

• Acceleration Structures Guide - Comprehensive guide to BLAS/TLAS construction, memory management, and optimization
• Shader Binding Table Guide - Complete reference for SBT creation, alignment, and advanced usage patterns
• Ray Tracing Tutorial - Step-by-step progressive conversion guide from rasterization to ray tracing