Advanced Effects CMSC 435/634. General Approach Ray Tracing – Shoot more rays Rasterization –...
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Transcript of Advanced Effects CMSC 435/634. General Approach Ray Tracing – Shoot more rays Rasterization –...
![Page 1: Advanced Effects CMSC 435/634. General Approach Ray Tracing – Shoot more rays Rasterization – Render more images.](https://reader030.fdocuments.in/reader030/viewer/2022032518/56649ccc5503460f949961b1/html5/thumbnails/1.jpg)
Advanced Effects
CMSC 435/634
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General Approach
• Ray Tracing– Shoot more rays
• Rasterization– Render more images
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Shadows
• Are p or q in shadow?– Can they “see” the light?
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Ray Traced Shadows
• Rays from p/q to l known as shadow rays• “Bias” ray start to avoid self shadowing
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Adding Shadows
No shadows• Find an intersection• For each light
– Compute lighting
Shadows• Find an intersection• For each light
– Cast a shadow ray– If visible, compute lighting
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Rasterization Shadows
• Render Shadow Map– Image from the light– Record depth of closest object
along each ray• Use a shadow map– Render a pixel/fragment– Transform to light p/rojection– Is pixel farther away– Bias to avoid self shadowing
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The Dark Side of the Trees - Gilles Tran, Spheres - Martin K. B.
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Reflection
• Mirror-like reflection of light• Total color = diffuse + specular + reflection
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Ray Tracing Reflection
• Viewer looking in direction d sees whatever the viewer “below” the surface sees looking in direction r
• In the real world – Energy loss on the bounce– Loss different for different colors
• New ray– Start on surface, in reflection direction
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Ray Traced Reflection
• Limit bounces or contribution
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Rasterized Distant Reflection
• Look up reflection direction in reflection or environment map
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Environment Mapping
• Surround scene with maps simulating surrounding detail
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Ray Tracing vs. Environment Mapping
Ray Tracing Environment Mapping
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Ray Tracing vs. Environment Mapping
Ray Tracing Environment Mapping
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Refraction
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Side
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Top
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Calculating Refraction Vector
• Snell’s Law
• In terms of
• term
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Calculating Refraction Vector
• Snell’s Law
• In terms of
• term
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Calculating Refraction Vector
• Snell’s Law
• In terms of
• In terms of and
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Refraction by Wavelength
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Refraction Mapping
• Perturb refraction rays through transparent surface by disruption of surface normal
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Alpha blending
• How much makes it through• a = opacity– How much of foreground color 0-1
• 1-a = transparency– How much of background color
• Foreground*a + Background*(1-a)
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Refinements
• One a vs. a per color (RenderMan)• Multiple layers– Front to back
– Back to front
a1 c1 (1-a1)
a1 c1 + (1-a1) a2 c2 (1-a1) (1-a2)
a1 c1 + (1-a1) a2 c2 + (1-a1) (1-a2) a3 c3 (1-a1) (1-a2) (1-a3)
c3 a3
(c3 a3 (1-a2) + c2 a2)
(c3 a3 (1-a2) + c2 a2) (1-a1) + c1 a1
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Refraction and a
• Refraction = what direction• a = how much– Can use Fresnel
• Rasterization often just a without refraction– Render opaque stuff (any order)– Layer transparent stuff over opaque back-to-front
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Motion Blur
• Things move while the shutter is open
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Ray Traced Motion Blur
• Include information on object motion• Spread multiple rays per pixel across time
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Rasterized Motion
• Blend frames at different times– Need a lot to avoid strobing
• Analytically elongate and fade objects• Rasterize motion vectors and post-process
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Depth of Field
Soler et al., Fourier Depth of Field, ACM TOG v28n2, April 2009
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Pinhole Lens
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Lens Model
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Real LensFocal Plane
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Lens ModelFocal Plane
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Ray Traced DOF
• Move image plane out to focal plane• Jitter start position within lens aperture– Smaller aperture = closer to pinhole– Larger aperture = more DOF blur
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Rasterized DOF
• Blend images from jittered viewponts– Need lots to avoid artifacts
• Render, blur, merge– Use depth to decide how much blur– Doesn’t get occlusion quite right