Textures, Mappings (06) RNDr. Martin Madaras, PhD. - - PowerPoint PPT Presentation

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Textures, Mappings (06) RNDr. Martin Madaras, PhD. - - PowerPoint PPT Presentation

Nov 08, 2022 124 likes •694 views

Principles of Computer Graphics and Image Processing Textures, Mappings (06) RNDr. Martin Madaras, PhD. martin.madaras@stuba.sk Overview Texture mapping 3D Models with texture coordinates UV map parametrization Perspective

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Principles of Computer Graphics and Image Processing

Textures, Mappings (06)

  • RNDr. Martin Madaras, PhD.

martin.madaras@stuba.sk

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 Texture mapping

 3D Models with texture coordinates  UV map parametrization  Perspective correction

 Aliasing  Anti-aliasing

 Supersampling  Mip Maps

 Advanced textures

 Environment mapping  Bump mapping  Normal mapping, Displacement mapping etc.

Overview

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How the lectures should look like #1

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 Visually distinguishes 2 objects with identical geometry  For now, we focus on object’s own color

Material

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 Used to define object’s color appearance

 2D bitmap  Volumetric - texels  Procedural texture

Texture

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Texture mapping

 Mapping between object space and 2D texture space  New coordinate system: Texture coordinates

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Texture mapping

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Texture mapping

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Texture mapping

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Texture mapping

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3D rendering pipeline

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3D polygons Modeling Transformation Lighting Viewing Transformation Projection Transformation Clipping Scan Conversion 2D Image

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 Lighting + color from image

 Could be implemented here

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3D rendering pipeline

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3D polygons Modeling Transformation Lighting Viewing Transformation Projection Transformation Clipping Scan Conversion 2D Image

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 GPU Texture mapping

 Fragment shader implementation

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 Add visual detail to surfaces of 3D objects

 1) Parameterized mesh  2) Final textured model

Texture mapping

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 Remember polygon rasterization

Intermediate pixels

S C A N L I N E projected scanline Screen space Texture space

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 object diffuse color

 patterns, decals

 modulate surface properties

 bumps, displacements

 modulate lighting properties

 e.g. shininess

 simulate physical phenomena

 reflection, refraction, global illumination

Texture usage

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Texture mapping

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 Unwrapping earth into a plane

Example – cartography

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Parameterization

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 Implicit parametrization by geometrical primitives

Parameterization

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 XYZ to UV for sphere:

Parameterization

2 2 2 2 2 2

z y x y v z y x x u + + = + + =

http://tobias.preclik.de/codeblog/?p=9

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 Parameterization using an intermediate surface

Parameterization

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Parameterization

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 When drawing pixels, map from ...

 image coordinate system (x,y) to  modeling coordinate system (u,v) to  texture coordinate system (t,s)

Texture mapping

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 Scan conversion

 Interpolate texture coordinates down/across scan lines  Distort due to bilinear interpolation approximation  Cut polygons into smaller ones, or  Perspective divide at each pixel

UV mapping

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 Scan conversion

 Interpolate texture coordinates down/across scan lines  Distort due to bilinear interpolation approximation  Cut polygons into smaller ones, or  Perspective divide at each pixel

Perspective correction

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Perspective correction

INCORRECT CORRECT

tQ P t T + − = ) 1 (

z z

Q Q t P P t T + − = ) 1 (

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 Texture mapping

 3D Models with texture coordinates  UV map parametrization  Diffuse color textures  Other textures

 Bump mapping  Environment mapping

 Aliasing  Anti-aliasing

 Supersampling  Mip Maps

Overview

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 “Moire pattern”

Nyquist frequency

Sampling frequency >= 2x signal frequency

Aliasing

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 Ideally, use elliptically shaped convolution filter  In practice we use rectangles

Texture filtering

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 Size of filter depends on projective wrap  Images can be pre-filtered

 Mip Maps  Summed area tables

Texture filtering

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 Keep textures pre-filtered at multiple resolutions

 For each pixel, linearly interpolate between two closest levels

(e.g., trilinear filtering)

 Fast and easy for hardware

Mip maps

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Environment mapping

https://www.youtube.com/watch?v=LOeEfkzZ1ps

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Light maps

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 Pre-computed high-quality lighting  Stored into special texture (light map)  Light map combined with the texture  Texture baking (permanent)

Light maps

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Light maps

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

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 A modified surface normal is calculated from the height map  Modified normal is used during shading  Geometry is not altered

Bump mapping

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 Combine multiple textures

Multitexturing

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Overview

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 Advanced Shading and Mapping

 Deferred Shading  Shadow Mapping  Normal Mapping  Displacement Mapping  Vector Displacement Mapping

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Deferred Shading

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 Compute Lighting in Screen-Space  Two pass approach  Decoupling of geometry and lighting  G-Buffer stores positions, normals, materials …  Lighting is a per-pixel operation  Problems with transparency and G-buffer size  O(objects+lights)

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Deferred Shading

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Diffuse Color Z Buffer Surface Normals Final Composition

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Normal Mapping

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 Fake lighting of bumps and dents  “Dot3 bump mapping”  Add lighting details without additional geometry  Store normals from high-polygon object in texture  Encode X,Y,Z as R,G,B color information

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Normal Mapping

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Normal Mapping

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a)

Normal map

(encoded in object space)

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Original high-res model

c)

Rendered low-res model

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Applied normal map

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Displacement Mapping

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 Move geometry as specified in texture  Displacement in direction of surface normal  Can add additional detail to a subdivided model  Relies on dense geometry  Usually used with adaptive tessellation techniques

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Displacement Mapping

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Displacement Mapping

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bump mapping displacement mapping

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Vector Displacement Mapping

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 Displace geometry in any direction  Generalization of displacement mapping  Possible to store detailed geometry in textures  Excellent for sculpting purposes (Z-Brush)

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Vector Displacement Mapping

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Shadow Mapping

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 Two pass technique  Obtain Light view depth buffer  Compare each pixel rendered to with light depth  Pixels further away are in shadow  Needs margin of error for lit pixels  Implementation usually has artifacts

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Shadow Mapping

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Lights, visibility, texture...

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What’s missing is shadow

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Shadows

Next Week

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Acknowledgements

 Thanks to all the people, whose work is shown here and whose

slides were used as a material for creation of these slides:

Matej Novotný, GSVM lectures at FMFI UK Peter Drahoš, PPGSO lectures at FIIT STU

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www.slido.com #PPGSO06 martin.madaras@stuba.sk

Questions ?!