Ray Tracing Basics

Different paradigm from rasterization:

For each pixel:
    cast ray from camera through pixel
    find closest hit
    compute color (recursive for reflections)
    return color

Each pixel = one or more rays. Each ray finds geometry.

Camera ray generation:

• Camera position + viewing direction.
• For pixel (x, y), compute ray through it in world space.

Pinhole camera:

• Simple model: rays through single point.
• No lens distortion / depth of field.
• Standard for CGI.

Anti-aliasing:

• Multiple rays per pixel, average colors.
• 4x supersampling = 4 rays per pixel.
• Stratified or Halton sequences for low-discrepancy sampling.

Bounded recursion:

• Reflections: bounce ray, recurse.
• Limit depth (5-10 bounces) to prevent infinite recursion.

Shadow rays:

• For each light: cast ray from hit point to light.
• If blocked: shadow.
• If not: light contributes.

The 0.001 offset (epsilon) prevents self-intersection.

Performance: O(rays * triangles). Acceleration: BVH (next).

Path tracing:

• For each ray: bounce randomly, accumulate emission.
• Many samples per pixel (1000+).
• Physically correct but slow.
• Production rendering (films): minutes per frame.
• Modern GPU: real-time path tracing with denoising (NVIDIA RTX).