Source 2006
The Source 2006 engine branch, also known as the Episode One engine branch, was released in 2006 with 
Half-Life 2: Episode One. It was obsoleted by the Orange Box/Source 2007 branch. It requires Half-Life 2 content to operate.
The SDK and SDK Base game for this branch are free to all Steam users.
Features
New since Half-Life 2:
- High Dynamic Range rendering
- A simulation of brightness values outside computer monitors' actual range, and of aperture adjustment.
- Phong shading
- Diffuse reflections for skin and other roughened surfaces.
- Facial animation upgrades
- More detail and intenser shapes for close-up performances.
- Dynamic interactions
- Dynamic interactions between NPCs using special animations.
- Lightwarp textures
- 1D textures that tint a material per-texel depending on their brightness.
- DirectX 9 Shader Model 3
- Unlocks greatly improved shader performance.
- Detail prop shapes
- Improved detail sprites that sway in the breeze and bend away from nearby players.
Availability
Gamecode for this branch is included in the Source SDK.
