Chapter 12 Multipass Rendering

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Chapter 12Multi-pass Rendering

• Oct. 18. 2001
• HyungSeok Kim

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Multi-pass Rendering

• Single-pass rendering
• Multi-pass rendering

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Chapter Overview

• Image combining methods
• Multi-pass algorithms
• Multi-texture

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Combining Rendered Images

• Rendered image
• RGB?Z pixels
• New image current image ltgt incoming image
• Combining method
• Z buffer method
• Alpha method (over)
• Composite method (comp)

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Combining Method

• Blending
• (R,G,B,?)new (R,G,B,?)source blendsource
  (R,G,B,?)dest blenddest
• Z-buffer

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Combining Method

• Accumulation buffer
• Stencil buffer

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Multi-pass Algorithms

• Back to front transparency
• Traditional process for transparency
• Render opaque object normally
• Sort the transparent polygons
• Render transparent polygons in back-to-front
  order

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Multi-pass Algorithms

• Back to front transparency
• Multi-pass algorithm without sorting
• Using two Z buffers with different functions
• Render opaque object with Zc
• Iterate to find furthest transparent polygons
• Swap Z buffers, disable frame buffer
• Draw transparent object with Zc (find furthest
  polygons,
• Mark rendered polygons in stencil buffer
• Disable Z buffer, enable frame buffer
• Draw transparent object marked in stencil buffer

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Transparent Stage
Zhigh
Zlow
Stencil buffer
Passes if Z lt Zlow Z gt Zhigh
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Multi-pass Algorithms

• Planar reflections Mirror
• Rendering reflected one first
• Rendering normal scene first
• Render the scene (excluding the mirror)
• Render mirror (with stencil)
• Clear Z-buffer of mirror area
• Render reflected scene

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Mirror
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Mirror
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Multi-pass Algorithms

• Multi-pass shadow volumes
• Render scene with ambient light only
• Calculate the shadow volume polygons
• Set no write on the depth frame buffer, depth
  test on. Init stencil buffer
• Render the shadow volume with back face culling
  increment stencil buffer if it passes depth test
• Render the shadow volume with front face culling
  decrement stencil buffer if it passes depth
  test
• Render the scene if the stencil buffer is zero

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Multi-pass Algorithms

• Multi-pass shadow volumes

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Multi-pass Algorithms

• Light objects
• Render the scene
• Invert Z-buffer test. Activate stencil test
• Render the light object with back face culling
• Render the light object with front face culling

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Multi-pass Sampling

• Sample points in multi-pass
• Using accumulation buffer

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Multi-pass Sampling

• Anti-aliasing
• Motion blur

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Multi-pass Sampling

• Depth of Field
• Soft shadow

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Multi-texture

• Multi-texture

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Multi-texture example

• Detail modulation
• View-dependent detail light maps
• Light map bump map
• Multi-pass alternatives
• Multi-texture as a complete lighting model
• Fog(Texture map (Light map) Specular map
  Environment map)
• (Texture map Specular map) Light map

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Multi-pass Rendering