Real-Time Rendering

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Real-Time Rendering

• TEXTURING
• Lecture 02
• Marina Gavrilova

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Brief Outline

• Basic Concept
• Texture Wrapping
• Magnification filter
• Minification filter
• Multi-Texturing
• Dynamic Texture
• Texture mapping methods

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Concept of Texture

• Texture Variation of surface diffusion, color,
  glossiness and other reflective photometry
• The heart of todays computer graphics
• Texture Pixel Texel
• Polygon is filled using texel values.
• Texture coordinate associates a screen pixel with
  a texel

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Texturing a surface
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Texture mapping
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Texture mapping in computer games
Color texture
Environment mapping
Alpha mapping
Bump mapping
Multi-texturing
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Basic Texturing concept

• Modify the value used in the lighting equation
• Basic Texture per pixel object color
• Steps
• Assign UV texture coordinates to vertices of a
  polygon (i.e. triangle)
• Interpolate texture UV coordinate for each fill
  pixel during rasterization of the triangle
• Lookup texel value from texture using UV coord.
• Use texel value in lighting equation

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Texture Method

• Texture pipeline used in rendering platforms to
  use hardware accelerations
• U,V?0,1 ? scaled texel coordinate
• Texture resolution is a power of 2 (i.e. 256 x
  256 texels)

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Texture Pipeline

• Compute object space location
• Use projector function to find (u,v)
• Use corresponding functions to find texel
• Apply value transform function
• Modify illumination equation value

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Texture Rendering
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Texture modes

• When UV value goes beyond the range 0,1
• i.e. uv (-1,-1) ? (2,2) (see below)
• Allow simple and small textures to render large
  complex objects

Tile
Mirror
Clamp
Border
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Three dimensional texture coordinate (u,v,w)

• 2D texture wrapping can be difficult for complex
  object
• 3D texture mapping use (u,v,w) coordinate for
  texture address
• Result is uniform texture distribution on a
  surface

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Texture magnification

• When 1 texel n pixels (ngt1)
• Visual Pixelation effect prominent
• Solution apply magnification filter

Bilinear
No Filter
Bilinear
No Filter
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Bilinear Filtering

• Four pixel linear Interpolation (2x2)
• Fast but low quality

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Bicubic

• Not yet used in realtime graphics
• Up to 4x4 pixel interpolation
• Good quality
• Slow

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Minification filter

• When n texel 1 pixel
• Aliasing distortion is present
• Annoying artifact during animation
• Solution MIP mapping, min-filters

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Min filters

• Nearest
• MIP
• Summed area

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MIP Mapping (Base Concept)

• Have multiple copy of a texture with reduced
  resolution (factor of 2)
• I.e. (256x256), (128,128), (64,64),(1,1)
• Determine LOD from neighboring pixel UV
  difference (spacing)

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Anisotropic Filtering
Trilinear MIP-MAPPING
Anisotropic Filtering
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Texture caching and compression

• Complex scene require large amount of texture
• Texture Memory is limited
• Texture management Load only smaller LODs for
  distant objects
• Use Clip-maps load a small segment of high LOD
  texture
• S3TC (61) compression ? DirectX standard
• Use two colors for a 4 color ramp
• Represent 16 pixels using 4 colors
• 2 bit per pixel, 16 bit per color ? Average 4 bit
  per pixel

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Multi-pass rendering

• Rendering the same geometry several times
• Integrate different photometric components
• I.e. Quake III has 10 rendering passes

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Multi-texturing

• Combine two or more textures
• Could be performed in one rendering pass
• Pixel value is computed using values from
  different texture stages

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Multi-texture Pixel-shader
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Texture Effects

• Variety of realistic 3D effects can be created by
  manipulating textures of a 3D geometry

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Texture Animation

• Dynamic animated texture
• Store combined static frames as 1 image
• Use different UVs to animate frames

UV(0.25,0.25)
UV(0.5,0.5)
Frame 5
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Transparency Alpha mapping


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Billboarding

• Create complex objects using texture and simple
  geometry
• Used extensively in particle rendering systems
• Use faceted quads ? normal of the quad equals
  camera direction
• Used frequently in games
• High performance

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Multi Textured Gloss Mapping
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Reflection/Environment mapping
Blinn Newells method
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Other environment mapping
Cube Mapping
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Bump Mapping

• Per-pixel normal
• Use cubemaps for normal

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Bump mapping

• Use cubemap and multi-texture pass
• Or use High level shading Language (HLSL) in
  nvidia

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Other texture teqniques

• Detail Textures (i.e. flight simulator)
• Procedural Texture
• Anti-aliasing
• Motion blur
• Realistic shading
• Volumetric Texture
• Image processing using texture passes
• Exposure control (Dynamic Range)

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End of Lecture 02

• Questions?