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Paper Summaries Logistics One More Announcement Assignments Projects Paper Summaries • Any takers? Texture Mapping Logistics One more announcement • Job related news • Electronic Arts (EA) is coming to RIT. – Co-op orientation – Looking for a few (actually more than a few) good gaming programmers • Friday, Sept 16th 12:00 – 1:30pm 70-1400 • Friday, Oct 14th 1:00 – 2:30pm Eastman Aud. – EA Company Presentation – Career Fair • Tuesday, October 4th • Wednesday, Sept 28th • 6-7:30pm • 11am – 4pm • Golisano auditorium • Gordon Field House – Interviews th – EA Job offer • Wednesday, October 5 (Career Center) • SIGN UP IF INTERESTED!!! Assignments Projects • Checkpoint 2 • Approx 17 projects – Due today. • Listing of projects now on Web • Checkpoint 3 • Presentation schedule – Due Thursday – Presentations (20 min max) – Roundoff error! – Last 3 classes (week 10 + finals week) – Sign up • Checkpoint 4 / RenderMan • Email me with 1st , 2nd , 3rd choices – To be given Thursday • First come first served. 1 Computer Graphics as Virtual Photography Remember this? real camera photo Photographic Photography: scene (captures processing print light) • Bi-directional Reflectance Function processing BRDF = fr (φi ,θi ,φr ,θ r ) Computer 3D camera tone synthetic Graphics: models model reproduction image At a given point, gives relative reflected illumination in any (focuses simulated direction with respect to incoming illumination coming from lighting) any direction Illumination Models Phong Model • 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. = + • + • ke L(V ) ka La kd ∑i Li (Si N) ks ∑i Li (Ri V) ambient diffuse specular Question Texture Mapping • What if Phong (or other) Illumination models aren’t good enough? • Developed in 1974 by Ed Catmull, currently – Texture Mapping – use an image president of Pixar – Procedural Shading – program your own • Goal: Make Phong shading less plastic looking 2 Texture Mapping 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 (xo,yo,zo) – Screen space (x, y) Watt Texture Mapping Texture Mapping • Key to texture mapping is parameterization texture space (u,v) – 3D geometry must be expressed as a function parameterization of 2 variables, u and v. –Examples: object space (xo,yo, zo) •Planar projection • Spherical • Bi-cubic patch screen space (x,y) • Cylindrical Texture pipeline Texture pipeline example Akenine-Moller / Haines Akenine-Moller / Haines 3 Projector function Projector function • Converts 3D point in object space (x,y,z) to • Spherical Mapping 2D point in texture parameter space (u,v) •Examples: – Spherical mapping – Cylindrical mapping – Planar mapping – Parametric surface mapping Projector function – Spherical Mapping Projector function • Cylindrical mapping Texture is like a rubber sheet stretched to fit model Projector function Projector function • Spherical mapping • Bi-cubic surfaces 4 Projector function – bicubic surfaces Projector function • Texture Mapping Applets http://www.cs.brown.edu/exploratories/free Software/catalogs/texture_mapping.html Watt Corresponder function Texture Mapping - Direct Mapping • 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 – Using a Texture Mapping – Applying Transformation Portion of the Image ⎛ x ⎞ ⎛ u ⎞ ⎜ ⎟ ⎜ ⎟ ⎜ y⎟ ⎛Projection ⎞⎛Rotation ⎞⎛Translation⎞⎜v ⎟ ⎜ ⎟ = ⎜ ⎟⎜ ⎟⎜ ⎟⎜ ⎟ z ⎝ Matrix ⎠⎝ Matrix ⎠⎝ Matrix ⎠ n ⎜ ⎟ ⎜ ⎟ ⎝1 ⎠ ⎝1 ⎠ Foley/VanDam(745) 5 Texture Mapping – out of range Texture mapping • Aliasing – Sampling – images are discrete, not continuous. – Resolution of sampled space (in this case texture map) is not fine enough Repeat Mirror clamp border (tile) (tile) Texture mapping • Aliasing- point sampling in middle of pixel - need more! Texture Mapping – Aliasing Watt Texture Mapping Texture Mapping - Anti-aliasing • Aliasing -because of interpolation and perspective • Point sample at higher resolution (sometimes very projection 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 aliased image anti-aliased image • Can sometimes use stochastic sampling to improve results 6 Texture mapping Texture Mapping • Texture Map Aliasing Applet •Mipmaps http://www.nbb.cornell.edu/neurobio/land/ – Pre-calculate your texture map at many resolutions (or layers) OldStudentProjects/cs490- – Store all “texture layers” in a single image. 96to97/anson/TextureMappingApplet/ – 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 Texture Mapping •Mipmaps Texture pipeline When we last left our hero • Break 7 Value transform function Value Transform functions • Texture maps need not be just plain old • Texel data interpretation: RGB. – Normal displacement – Bump Mapping • Texture == data associated with an object – Transparency Mask – Alpha Mapping – Stored in a 2D array of texels – Reflection – Environment Mapping • Value transform function – Illumination – Light Mapping – Transforms data into value usable by the – Specular component – Gloss Mapping illumination model at the shading point – Lighting intensities – Radiance Mapping Texture Mapping- Bump Mapping Texture Mapping- Bump Mapping • Perturbing surface normal Adds roughness to surfaces • Texture map represents displacements from the Quick way to add detail to an normal object • Use perturbed normal in illumination model Polygon remains physically flat, but appears bumpy Jim Blinn Texture mapping – Bump Mapping Bump Mapping Theory • If your eyes see light and dark Æ bumps • Flat surfaces reflect more light • Bumpy surfaces reflect less 8 Bump Mapping-Theory Bump Mapping • Perlin Dnoise example [Perlin85] Normal += Dnoise (point) Texture Mapping Alpha Mapping • Bump Mapping • Used to control the transparency. • Example: 3dimpact.com Texture Mapping- Environment mapping Texture Mapping- Environment mapping • Create an image, representing the reflection of the • Not associated with a particular object but with world onto an object an imaginary surface surrounding the scene • Use surrounding sphere or box, image is texture map – Specular Reflection – indexed by reflected ray indexed by direction of reflection ray – Diffuse - by surface normal • Poor-man’s ray tracing - cheaper – Transparency – refracted ray direction 9 Environment Mapping Environment Mapping spherical Cube map Texture Mapping Texture mapping • Environment mapping Reflection mapping Light Mapping Gloss Mapping • Texture map that describes illumination • The texture that controls the specular (light sources)to apply reflection color. • Modulates the the specular reflection and the environment map. •Demo flipcode.com 10 Texture Mapping Texture Mapping – Radiance Maps • Static • Provides approximated radiance values, not – Texture map image is taken under a single simply color info, as a texture. lighting condition • Radiance map not only for the distant scene, but in reflections from objects. – Q: What happens when lighting conditions of • Radiance in map used in global illumination the scene doesn’t match that of your texture? solution – A: let’s go to the video tape • Technique used in Fiat Lux Texture pipeline Layered Texture Mapping • Finally obtained data is applied in illumination equation. Layered Texture Mapping Multipass Texture Rendering • Applet • Multiple textures for multiple parts of http://users.interfriends.net/maurid/Bump illumination model rendered on multiple Mapping.htm passes. • Modern hardware supports up to 10 passes on a single frame. 11 Multipass Texture Render Summary • Quake III Engine • Texturing Pipeline – Passes 1-4: accumulating bump map • Advantages of texture mapping – Pass 5: diffuse lighting – Easy way to add complexity to a scene – Pass 6: base texture – Hardware support – Pass 7: Specular • Issues: – Pass 8: emissive lighting – Aliasing – Pass 9: volumetric effects – Limited resolution (zoom in DOOM effect) – Pass 10: screen flashes – Static image 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? 12.
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