GDC 2005

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(No Transcript)
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Building a Dynamic Lighting Engine for Velvet
Assassin

• Christian Schüler

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Velvet Assassin

• 3rd person stealth game
• Formerly known as Sabotage 1943
• First concepts late 2000
• Release April 2009
• Platforms PC, X360
• My role tech. dir. plus lead engine programmer

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Engine Goals

• Must look great!
• (of course)
• Everything is dynamically lit
• Cannot use Lightmaps
• Lighting is part of gameplay
• If it looks dark, the player should be hidden!
• Light sources become game entites.

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Engine Goals?

• So, what about ...
• scene visibility
• light influence
• indirect lighting (like radiosity)
• if every object can possibly move,
• even light sources?

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First Engine (2003)
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Axioms (2003)

• World is a loose octree of objects
• Objects are OBB trees of triangles
• Multi-pass lighting with stencil shadows
• Occlusion culling for visibility
• Indirect illumination via bounce lights

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Shipping Engine (2009)
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Axioms (2009)

• World is a loose octree of objects
• Objects are OBB trees of triangles
• Hybrid single/multi-pass lighting with shadow
  maps
• Portals for visibility
• Indirect illumination via bounce lights
• XBox 360 specific optimizations

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Loose Octrees

• Thatcher Ulrich (2001)
• Cells are overlapping (loose)
• Insertion is efficient
• No need to rebuild the whole octree if an element
  moves!
• ? Perfect as spatial index of a dynamic scene!

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Loose Octrees contd.
Extended volume
Base cell
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Loose Octrees contd.
Object inserted if inside extended volume ? O(1)
insertion
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Loose Octrees contd.

• Used in finding out
• Objects in a view frustum
• Objects influenced by a light
• Lights influencing an object
• Broad phase for ray tests
• Gameplay objects in range
• And everything can be dynamic!

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OBB Trees

• Oriented Bounding Box Tree
• S. Gottschalk et al (1995)
• Used on the polygon level
• Build as a pre-process over mesh data
• Allows efficient ray-mesh and mesh-mesh
  interference tests

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OBB Trees contd.
Axis aligned
vs oriented!
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OBB Trees contd.

• Construction
• Principal axes (gaussian point distribution)
• Minimize Box volume
• (possibly iterative)

eigenvectors of covariance matrix
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Hybrid Lighting

• A hybrid between multi-pass
• and single-pass forward renderer
• One pass for each primary light
• One pass for all secondary lights combined

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Hybrid Lighting contd.

• Primary lights
• Classic multi-pass (Doom 3 style)
• One pass per primary light
• Can cast shadows
• The light queries for surrounding geometry

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Hybrid Lighting contd.

• Secondary lights
• Classic single-pass (HL2 style)
• Lights collected into one pass
• (shader variation based on count)
• Can not cast shadows
• The geometry queries for surrounding lights
• (up to a maximum amount)

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Hybrid Lighting contd.
secondarypoints
primary spot
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Hybrid Lighting contd.
primary directional
secondarypoints
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Bounce Light
Gives appearance of first bounce indirect light
from a surface. Must not illuminate the surface
it is placed on. Has a half-sphere influence
radius determined by axis.
N
L
axis
(NL) f(axisL)
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Bounce Light contd.
primary spot
secondarybounce
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Bounce Light contd.
2 secondaryambients
primaryspot
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Bounce Light contd.
... and even back in 2003 (its not rocket
science)
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So, for each frame

• Get all primary lights in view
• Distribute shadow map pool
• Render shadow maps, for each
• Render all objects contained in light frustum
• Get all objects in view
• Render base pass
• For each object, collect nearest N secondary
  lights (sorted by importance) for the shader
• Render additive passes for each
• primary light for each object that is in the
  view and also in the light frustum.
• That is why you need an efficient spatial
• index data structure.

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Fog Zones

• A.k.a. There has to be at least
• one benefit for manual
• portalization!
• Here it is Fog Zones!

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Fog Zones contd.
portal separates fog environments
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Fog Zones contd.
from the other side
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Fog Zones contd.

• Multiply-Add is your friend!
• (instead of lerping against a constant fog
  color)
• C C0 T S
• C0 original color
• T fog transmittance
• S fog in-scatter
• (1-T) CFog traditionally

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Fog Zones contd.

• C ( C0 TB SB ) TA SA

A
B
portal
C C0 ( TB TA ) ( SB TA SA )
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Fog Zones contd.

• Modify T and S of the new environment with T and
  S from the portal polygon
• Calculate fog from the distance of the portal
• Repeat recusively

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Fill Optimization

• Only done for XBox 360
• Selected particle effects rendered into
  off-screen render target at half resolution to
  save fill rate
• (against half resolution depth buffer)
• Composited over the final image

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Fill Optimization contd.
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Fill Optimization contd.

• Again, multiply-add solves the math
• (in the form of pre-multiplied alpha)
• Off-screen target
• CTarget (1-AParticle) CTarget CParticle
• ATarget (1-AParticle) ATarget AParticle
• Compositing
• CFrame (1-ATarget) CFrame CTarget

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Multi-threading

• XBox 360 needed it a dual-core PC at least
  benefits
• First thread performs all spatial queries and
  compiles a drawlist
• Second thread sets shader registers, render
  states and submits batches
• Most scenes from 300 to 1200 batches/frame

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The End

• Questions?