The Equation

Phong Reflection Model

The Equation

Phong Reflection Model

Illumination = ambient light + the sum of all light's reflection towards the viewer

Easy concept, complex math

Main point: it's costly

Early methods

Offline rendering

• Gouraud Shading, a kind of vertex-based lighting
  • Calculate light at points, interpolate between points
• Light Maps
  • "Baked In" lighting that uses multitexturing
  • Calculated in level or model editor with raytracing, results saved in file
  • Static geometry, not moving

Gouraud

Baked into vertices themselves, common in PSX and N64 era

Light Maps

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http://www.cs.bath.ac.uk/~pjw/NOTES/pics/lightmap.html

Forward Rendering

The "brute force" way

Two streams of input: meshes and lights​

Output: 2D representation of mesh on-screen

• For each mesh,
  • add up each light's contribution
  • multiply total light by diffuse texture color

Forward Rendering

Looks good, but costly

Games either used offline lighting entirely or used forward rendering very sparingly

Forward Rendering

http://www.polycount.com/forum/showthread.php?t=104415

Deferred Rendering

Apply lighting to only seen pixels

Save lighting calculation as last step

Render model information to screen, light as last step

Forward Rendering cost:

  N meshes * M lights

Deferred Rendering cost:

  N meshes + N lights + static cost of creating G-Buffer

Deferred Rendering

Two stages:

  Stage 1:

  - Two streams of input, lights and meshes again

  - Output: a set of fullscreen textures known as a Geometry   Buffer, or "G-Buffer"

  Stage 2:

  - Input: G-Buffer

  - For each light, do calculation on G-buffer

  - Output: Final lit scene

Deferred Rendering

G-Buffer: Diffuse, Normal, Depth

Fully lit scene in bottom right

http://www.neuroproductions.be/uploads/openglGame/DeferredShadingOpengl.jpg

Deferred Rendering

G-Buffer: Diffuse, Normal, Depth, Light

Fully lit scene on bottom

http://3.bp.blogspot.com/-RuoVTYRh-wE/Teq7UVwSN8I/AAAAAAAABMY/VlfL8R6wGJA/s1600/deferredshading101.png

Deferred Rendering

Some disadvantages:

  Can't blend transparent objects

  - Engines that do mix forward and deferred

  G-buffer takes up a lot of memory

"Forward+" Rendering

Most recent, still experimental

Extension of both Forward and Deferred

Essentially, Forward + Light Culling

"Forward+" Rendering

Most recent, still experimental

Extension of both Forward and Deferred

Essentially, Forward + Light Culling

Same as Forward Rendering, with intermediate step:

Screen is subdivided into clusters or tiles

Cull lights by drawing them as sphere and placing them into list of lights on cluster or tile

Draw only with lights for pixel that cluster is in

"Forward+" Rendering