Logistics Checkpoint 2 Mostly graded. Note on grading -- Regaining - PDF document

Texture Mapping Logistics  Checkpoint 2  Mostly graded.  Note on grading -- Regaining points  Checkpoint 3  Due Monday  Project Proposals  All should have received e-mail feedback. 1

Logistics  Checkpoint 2  Another means for finding equation of a plane  Using determinants.  See: http://local.wasp.uwa.edu.au/~pbourke/geometry/planeeq/ Logistics  Grad students  Please send topic of grad report. 2

Projects  Proposals  Proposal due before break (please get yours in if not submitted)  Feedback on proposals -- mycourses  Web sites please.  23 projects (4-5 more expected) Projects  Presentations:  Dates:  Week 9: Wed, Feb 13 (sorry Radiosity)  Week 10: Mon, Feb 18  Week 10: Wed, Feb 20  Finals Week / Week 11: Mon, Feb 25  15 minutes / presentation  Schedule on Web by next class  Please send me choice of time/day 3

Computer Graphics as Virtual Photography real camera photo Photographic Photography: scene (captures processing print light) processing camera Computer 3D synthetic tone model Graphics: models image reproduction (focuses simulated lighting) Remember this?  Bi-directional Reflectance Function BRDF f ( , , , ) = � � � � r i i r r At a given point, gives relative reflected illumination in any direction with respect to incoming illumination coming from any direction 4

Illumination Models  Illumination model - function or algorithm used to describe the reflective characteristics of a given surface.  More accurately, function or algorithm used to approximate the BRDF. Phong Model ∑ ∑ k L ( V ) = k L + k L ( S • N) + k L ( R • V) e a a d i i s i i i i ambient diffuse specular 5

Question  What if Phong (or other) Illumination models aren’t good enough?  Texture Mapping – use an image  Procedural Shading – program your own Texture Mapping  Developed in 1974 by Ed Catmull, currently president of Pixar  Goal: Make Phong shading less plastic looking 6

Texture Mapping  A means to define surface characteristics of an object using an image  Mapping a 2D image onto a 3D surface  Coordinate spaces in texture mapping  Texture space (u, v)  Object space (x o ,y o ,z o )  Screen space (x, y) Texture Mapping Watt 7

Texture Mapping  Key to texture mapping is parameterization  3D geometry must be expressed as a function of 2 variables, u and v.  Examples:  Planar  Spherical  Bi-cubic patch  Cylindrical Texture Mapping texture space (u,v) parameterization object space (x o ,y o , z o ) projection screen space (x,y) 8

Texture pipeline Akenine-Moller / Haines Texture pipeline example Akenine-Moller / Haines 9

Projector function  Converts 3D point in object space (x,y,z) to 2D point in texture parameter space (u,v)  Examples:  Spherical mapping  Cylindrical mapping  Planar mapping  Parametric surface mapping Projector function  Spherical Mapping 10

Projector function – Spherical Mapping Texture is like a rubber sheet stretched to fit model Projector function  Cylindrical mapping 11

Projector function  Spherical mapping Projector function  Bi-cubic surfaces 12

Projector function – bicubic surfaces Watt Projector function  Texture Mapping Applets http://www.cs.brown.edu/exploratories/ freeSoftware/catalogs/texture_mapping. html 13

Corresponder function  Converts from texture parameter space (u, v) to texel space.  Controls the way an image is applied  Examples:  Direct mapping  Use a portion of an image  Apply transforms  Out of range transforms Texture Mapping - Direct Mapping 14

Texture Mapping – Using a Portion of the Image Texture Mapping – out of range Mirror clamp border Repeat (tile) (tile) 15

Texture mapping  Aliasing  Sampling – images are discrete, not continuous.  Resolution of sampled space (in this case texture map) is not fine enough Texture mapping  Aliasing- point sampling in middle of pixel - need more! 16

Texture Mapping – Aliasing Watt Texture Mapping  Aliasing -because of interpolation and perspective projection aliased image anti-aliased image 17

Texture Mapping - Anti-aliasing  Point sample at higher resolution (sometimes very difficult)  Nearest  Pick the closest texel  Linear  Take an average of surrounding texels  Mip-Mapping  Multiple textures of the same image  Use low pass filter before sampling  Can sometimes use stochastic sampling to improve results Texture mapping  Texture Map Aliasing Applet http://www.nbb.cornell.edu/neurobio/la nd/OldStudentProjects/cs490- 96to97/anson/TextureMappingApplet/ 18

Texture Mapping  Mipmaps  Pre-calculate your texture map at many resolutions (or layers)  Store all “texture layers” in a single image.  Use “appropriate” layer when performing rendering, interpolating between levels as required  Mip == “multum in parvo”  Latin for “many things in a small space”  Native support in hardware. Mipmapping 19

Texture Mapping  Mipmaps Texture pipeline  Break 20

When we last left our hero Value transform function  Texture maps need not be just plain old RGB.  Texture == data associated with an object  Stored in a 2D array of texels  Value transform function  Transforms data into value usable by the illumination model at the shading point 21

Value Transform functions  Texel data interpretation:  Normal displacement – Bump Mapping  Transparency Mask – Alpha Mapping  Reflection – Environment Mapping  Illumination – Light Mapping  Specular component – Gloss Mapping  Lighting intensities – Radiance Mapping Texture Mapping- Bump Mapping  Adds roughness to surfaces  Quick way to add detail to an object  Polygon remains physically flat, but appears bumpy Jim Blinn 22

Texture Mapping- Bump Mapping  Perturbing surface normal  Texture map represents displacements from the normal  Use perturbed normal in illumination model Texture mapping – Bump Mapping 23

Bump Mapping Theory  If your eyes see light and dark  bumps  Flat surfaces reflect more light  Bumpy surfaces reflect less Bump Mapping-Theory 24

Bump Mapping  Perlin Dnoise example [Perlin85] Normal += Dnoise (point) Texture Mapping  Bump Mapping 25

Alpha Mapping  Used to control the transparency.  Example: 3dimpact.com Texture Mapping- Environment mapping  Create an image, representing the reflection of the world onto an object  Use surrounding sphere or box, image is texture map indexed by direction of reflection ray  Poor-man’s ray tracing - cheaper 26

Texture Mapping- Environment mapping  Not associated with a particular object but with an imaginary surface surrounding the scene  Specular Reflection – indexed by reflected ray  Diffuse - by surface normal  Transparency – refracted ray direction Environment Mapping 27

Environment Mapping spherical Cube map Texture Mapping  Environment mapping 28

Texture mapping Reflection mapping Light Mapping  Texture map that describes illumination (light sources)to apply flipcode.com 29

Gloss Mapping  The texture that controls the specular reflection color.  Modulates the the specular reflection and the environment map. Gloss Mapping ozone3d.net 30

Texture Mapping  Static  Texture map image is taken under a single lighting condition  Q: What happens when lighting conditions of the scene doesn’t match that of your texture?  A: let’s go to the video tape Texture Mapping – Radiance Maps  Provides approximated radiance values, not simply color info, as a texture.  Radiance map not only for the distant scene, but in reflections from objects.  Radiance in map used in global illumination solution  Technique used in Fiat Lux 31

Texture pipeline  Finally obtained data is applied in illumination equation. Layered Texture Mapping 32

Layered Texture Mapping  Applet http://www.neilwallis.com/java/bump 1.htm Multipass Texture Rendering  Multiple textures for multiple parts of illumination model rendered on multiple passes.  Modern hardware supports up to 10 passes on a single frame. 33

Multipass Texture Render  Quake III Engine  Passes 1-4: accumulating bump map  Pass 5: diffuse lighting  Pass 6: base texture  Pass 7: Specular  Pass 8: emissive lighting  Pass 9: volumetric effects  Pass 10: screen flashes Summary  Texturing Pipeline  Advantages of texture mapping  Easy way to add complexity to a scene  Hardware support  Issues:  Aliasing  Limited resolution (zoom in DOOM effect)  Static image 34

Summary  In this lecture, we assumed that textures were pre-generated and saved in a file  Textures can also be generated on the fly using a function or procedure…  But that’s for next time…  Questions? 35