DOCSLIB.ORG

Texture Mapping Objectives the Limits of Geometric Modeling

Total Page：16

File Type：pdf, Size：1020Kb

Download full-text PDF Read full-text
Texture Mapping Objectives the Limits of Geometric Modeling Objectives •Introduce Mapping Methods Texture Mapping - Texture Mapping - Environment Mapping - Bump Mapping CS 432 Interactive Computer Graphics •Consider basic strategies Prof. David E. Breen - Forward vs backward mapping Department of Computer Science - Point sampling vs area averaging E. Angel and D. Shreiner: Interactive Computer Graphics 6E © Addison-Wesley 2012 1 E. Angel and D. Shreiner: Interactive Computer Graphics 6E © Addison-Wesley 2012 2 1 2 The Limits of Geometric Modeling an Orange Modeling •Although graphics cards can render over •Consider the problem of modeling an orange 20 million polygons per second, that (the fruit) number is insufficient for many phenomena •Start with an orange-colored sphere - Clouds - Too simple - Grass •Replace sphere with a more complex shape - Terrain - Does not capture surface characteristics (small - Skin dimples) - Takes too many polygons to model all the dimples E. Angel and D. Shreiner: Interactive Computer Graphics 6E © Addison-Wesley 2012 3 E. Angel and D. Shreiner: Interactive Computer Graphics 6E © Addison-Wesley 2012 4 3 4 Modeling an Orange (2) Three Types of Mapping •Take a picture of a real orange, scan it, •Texture Mapping and “paste” onto simple geometric model - Uses images to fill inside of polygons - This process is known as texture mapping •Environment (reflection mapping) •Still might not be sufficient because - Uses a picture of the environment for texture resulting surface will be smooth maps - Need to change local shape - Allows simulation of highly specular surfaces - Bump mapping •Bump mapping - Emulates altering normal vectors during the rendering process E. Angel and D. Shreiner: Interactive Computer Graphics 6E © Addison-Wesley 2012 5 E. Angel and D. Shreiner: Interactive Computer Graphics 6E © Addison-Wesley 2012 6 5 6 1 Texture Mapping Environment Mapping geometric model texture mapped E. Angel and D. Shreiner: Interactive Computer Graphics 6E © Addison-Wesley 2012 7 E. Angel and D. Shreiner: Interactive Computer Graphics 6E © Addison-Wesley 2012 8 7 8 Bump Mapping Where does mapping take place? • Mapping techniques are implemented at the end of the rendering pipeline - Very efficient because few polygons make it past the clipper G eometry Fragment Frame Vertices Rasteriz ation processing processing buffer Pixel Pixels processing E. Angel and D. Shreiner: Interactive Computer Graphics 6E © Addison-Wesley 2012 9 E. Angel and D. Shreiner: Interactive Computer Graphics 6E © Addison-Wesley 2012 10 9 10 Is it simple? Coordinate Systems •Although the idea is simple---map an •Parametric coordinates image to a surface---there are 3 or 4 - May be used to model curves and surfaces coordinate systems involved •Texture coordinates - Used to identify points in the image to be mapped •Object or World Coordinates - Conceptually, where the mapping takes place 2D image •Window Coordinates - Where the final image is really produced 3D surface E. Angel and D. Shreiner: Interactive Computer Graphics 6E © Addison-Wesley 2012 11 E. Angel and D. Shreiner: Interactive Computer Graphics 6E © Addison-Wesley 2012 12 11 12 2 Texture Mapping Mapping Functions •Basic problem is how to find the maps parametric coordinates •Consider mapping from texture coordinates to a point a surface •Appear to need three functions (x,y,z) x = x(s,t) y = y(s,t) t z = z(s,t) •But we really want s texture coordinates to go the other way window coordinates world coordinates E. Angel and D. Shreiner: Interactive Computer Graphics 6E © Addison-Wesley 2012 13 E. Angel and D. Shreiner: Interactive Computer Graphics 6E © Addison-Wesley 2012 14 13 14 Backward Mapping Two-part mapping • We really want to go backwards •One solution to the mapping problem is to - Given a pixel, we want to know to which point first map the texture to a simple on an object it corresponds intermediate surface - Given a point on an object, we want to know to which point in the texture it corresponds •Example: map to cylinder • Need a map of the form s = s(x,y,z) t = t(x,y,z) • Such functions are difficult to find in general E. Angel and D. Shreiner: Interactive Computer Graphics 6E © Addison-Wesley 2012 15 E. Angel and D. Shreiner: Interactive Computer Graphics 6E © Addison-Wesley 2012 16 15 16 Cylindrical Mapping Spherical Map parametric cylinder We can use a parametric sphere x = r cos 2p u x = r cos 2pu y = r sin 2pu y = r sin 2pu cos 2pv z = v/h z = r sin 2pu sin 2pv maps rectangle in u,v space to cylinder of radius r and height h in world coordinates in a similar manner to the cylinder but have to decide where to put s = u the distortion t = v maps from texture space Spheres are used in environmental maps E. Angel and D. Shreiner: Interactive Computer Graphics 6E © Addison-Wesley 2012 17 E. Angel and D. Shreiner: Interactive Computer Graphics 6E © Addison-Wesley 2012 18 17 18 3 Box Mapping Second Mapping •Easy to use with simple orthographic • Map from intermediate object to actual object projection - Normals from intermediate to actual •Also used in environment maps - Normals from actual to intermediate - Vectors from center of intermediate actual intermediate E. Angel and D. Shreiner: Interactive Computer Graphics 6E © Addison-Wesley 2012 19 E. Angel and D. Shreiner: Interactive Computer Graphics 6E © Addison-Wesley 2012 20 19 20 Aliasing Area Averaging •Point sampling of the texture can lead to A better but slower option is to use area averaging aliasing errors miss blue stripes point samples in u,v (or x,y,z) space preimage pixel Note that preimage of pixel is curved point samples in texture space E. Angel and D. Shreiner: Interactive Computer Graphics 6E © Addison-Wesley 2012 21 E. Angel and D. Shreiner: Interactive Computer Graphics 6E © Addison-Wesley 2012 22 21 22 WebGL Texture Mapping Go to ART Texture Mapping slides E. Angel and D. Shreiner: Interactive Computer Graphics 6E © Addison-Wesley 2012 23 Angel and Shreiner: Interactive Computer Graphics 7E © Addison-Wesley 2015 24 23 24 4 Objectives Basic Stragegy •Introduce WebGL texture mapping Three steps to applying a texture - two-dimensional texture maps 1. specify the texture - assigning texture coordinates • read or generate image - forming texture images • assign to texture • enable texturing 2. assign texture coordinates to vertices • Proper mapping function is left to application 3. specify texture parameters • wrapping, filtering Angel and Shreiner: Interactive Computer Graphics 7E © Addison-Wesley 2015 25 Angel and Shreiner: Interactive Computer Graphics 7E © Addison-Wesley 2015 26 25 26 Texture Mapping Texture Example •The texture (below) is a y 256 x 256 image that has been mapped to a z x geometry display rectangular polygon which is viewed in perspective t image s Angel and Shreiner: Interactive Computer Graphics 7E © Addison-Wesley 2015 27 Angel and Shreiner: Interactive Computer Graphics 7E © Addison-Wesley 2015 28 27 28 Texture Mapping and the Specifying a Texture Image WebGL Pipeline •Images and geometry flow through • Define a texture image from an array of separate pipelines that join during texels (texture elements) in CPU memory fragment processing • Use an image in a standard format such as JPEG - “complex” textures do not affect geometric - Scanned image complexity - Generate by application code • WebGL1 only supports 2 dimensional texture maps vertices geometry pipeline - Dimensions should be power of 2 for mip-mapping fragment • These restrictions removed in WebGL 2, and now image texel pipeline processor supports many texture types • We’ll still focus on 2D textures E. Angel and D. Shreiner: Interactive Computer Graphics 6E © Addison-Wesley 2012 29 Angel and Shreiner: Interactive Computer Graphics 7E © Addison-Wesley 2015 31 29 31 5 Define Image as a Texture A Checkerboard Image gl.texImage2D( target, level, internalformat, var image1 = new Uint8Array(4*texSize*texSize); w, h, border, format, type, texels ); for ( var i = 0; i < texSize; i++ ) { for ( var J = 0; J <texSize; J++ ) { target: type of texture, e.g. gl.TEXTURE_2D var patchx = Math.floor(i/(texSize/numChecks)); level: used for mipmapping (discussed later) var patchy = Math.floor(J/(texSize/numChecks)); internalformat: elements per texel if (patchx%2 ^ patchy%2) c = 255; w, h: width and height of texels in pixels else c = 0; border: width of the border. Must be 0. //c = 255*(((i & 0x8) == 0) ^ ((j & 0x8) == 0)) format: must be the same as internalformat image1[4*i*texSize+4*j] = c; type: data type of texel data image1[4*i*texSize+4*j+1] = c; texels: source of texel data image1[4*i*texSize+4*j+2] = c; image1[4*i*texSize+4*j+3] = 255; glTexImage2D(gl.TEXTURE_2D, 0, gl.RGBA, 512, 512, } 0, gl.RGBA, gl.UNSIGNED_BYTE, my_texels); Angel and Shreiner: Interactive Computer Graphics 7E © Addison-Wesley 2015 32 } Angel and Shreiner: Interactive Computer Graphics 7E © Addison-Wesley 2015 33 32 33 Using a GIF image Mapping a Texture // specify image in JS file • Based on parametric texture coordinates var image = new Image(); image.src = "SA2011_black.gif” • Specify as a 2D vertex attribute • Interpolated by the rasterizer window.onload = function() { Texture Space Object Space configureTexture( image ); t } 1, 1 (s, t) = (0.2, 0.8) 0, 1 A a // or specify image in HTML file with <img> tag // <img id = "texImage" src = "SA2011_black.gif"></img> c (0.4, 0.2) b var image = document.getElementbyId("texImage”) B C window.onload = configureTexture( image ); 0, 0 1, 0 s (0.8, 0.4) Angel and Shreiner: Interactive Computer Graphics 7E © Addison-Wesley 2015 34 Angel and Shreiner: Interactive Computer
Load more

Recommended publications
  • Advanced Texture Mapping
    Advanced texture mapping Computer Graphics COMP 770 (236) Spring 2007 Instructor: Brandon Lloyd 2/21/07 1 From last time… ■ Physically based illumination models ■ Cook-Torrance illumination model ° Microfacets ° Geometry term ° Fresnel reflection ■ Radiance and irradiance ■ BRDFs 2/21/07 2 Today’s topics ■ Texture coordinates ■ Uses of texture maps ° reflectance and other surface parameters ° lighting ° geometry ■ Solid textures 2/21/07 3 Uses of texture maps ■ Texture maps are used to add complexity to a scene ■ Easier to paint or capture an image than geometry ■ model reflectance ° attach a texture map to a parameter ■ model light ° environment maps ° light maps ■ model geometry ° bump maps ° normal maps ° displacement maps ° opacity maps and billboards 2/21/07 4 Specifying texture coordinates ■ Texture coordinates needed at every vertex ■ Hard to specify by hand ■ Difficult to wrap a 2D texture around a 3D object from Physically-based Rendering 2/21/07 5 Planar mapping ■ Compute texture coordinates at each vertex by projecting the map coordinates onto the model 2/21/07 6 Cylindrical mapping 2/21/07 7 Spherical mapping 2/21/07 8 Cube mapping 2/21/07 9 “Unwrapping” the model 2/21/07 images from www.eurecom.fr/~image/Clonage/geometric2.html 10 Modelling surface properties ■ Can use a texture to supply any parameter of the illumination model ° ambient, diffuse, and specular color ° specular exponent ° roughness fr o m ww w.r o nfr a zier.net 2/21/07 11 Modelling lighting ■ Light maps ° supply the lighting directly ° good for static environments
    [Show full text]
  • Visualizing 3D Objects with Fine-Grain Surface Depth Roi Mendez Fernandez
    Visualizing 3D models with fine-grain surface depth Author: Roi Méndez Fernández Supervisors: Isabel Navazo (UPC) Roger Hubbold (University of Manchester) _________________________________________________________________________Index Index 1. Introduction ..................................................................................................................... 7 2. Main goal .......................................................................................................................... 9 3. Depth hallucination ........................................................................................................ 11 3.1. Background ............................................................................................................. 11 3.2. Output .................................................................................................................... 14 4. Displacement mapping .................................................................................................. 15 4.1. Background ............................................................................................................. 15 4.1.1. Non-iterative methods ................................................................................... 17 a. Bump mapping ...................................................................................... 17 b. Parallax mapping ................................................................................... 18 c. Parallax mapping with offset limiting ...................................................
    [Show full text]
  • Real-Time Recursive Specular Reflections on Planar and Curved Surfaces Using Graphics Hardware
    REAL-TIME RECURSIVE SPECULAR REFLECTIONS ON PLANAR AND CURVED SURFACES USING GRAPHICS HARDWARE Kasper Høy Nielsen Niels Jørgen Christensen Informatics and Mathematical Modelling The Technical University of Denmark DK 2800 Lyngby, Denmark {khn,njc}@imm.dtu.dk ABSTRACT Real-time rendering of recursive reflections have previously been done using different techniques. How- ever, a fast unified approach for capturing recursive reflections on both planar and curved surfaces, as well as glossy reflections and interreflections between such primitives, have not been described. This paper describes a framework for efficient simulation of recursive specular reflections in scenes containing both planar and curved surfaces. We describe and compare two methods that utilize texture mapping and en- vironment mapping, while having reasonable memory requirements. The methods are texture-based to allow for the simulation of glossy reflections using image-filtering. We show that the methods can render recursive reflections in static and dynamic scenes in real-time on current consumer graphics hardware. The methods make it possible to obtain a realism close to ray traced images at interactive frame rates. Keywords: Real-time rendering, recursive specular reflections, texture, environment mapping. 1 INTRODUCTION mapped surface sees the exact same surroundings re- gardless of its position. Static precalculated environ- Mirror-like reflections are known from ray tracing, ment maps can be used to create the notion of reflec- where shiny objects seem to reflect the surrounding tion on shiny objects. However, for modelling reflec- environment. Rays are continuously traced through tions similar to ray tracing, reflections should capture the scene by following reflected rays recursively un- the actual synthetic environment as accurately as pos- til a certain depth is reached, thereby capturing both sible, while still being feasible for interactive render- reflections and interreflections.
    [Show full text]
  • Environment Mapping
    CS 418: Interactive Computer Graphics Environment Mapping Eric Shaffer Some slides adapted from Angel and Shreiner: Interactive Computer Graphics 7E © Addison-Wesley 2015 Environment Mapping How can we render reflections with a rasterization engine? When shading a fragment, usually don’t know other scene geometry Answer: use texture mapping…. Create a texture of the environment Map it onto mirror object surface Any suggestions how generate (u,v)? Types of Environment Maps Sphere Mapping Classic technique… Not supported by WebGL OpenGL supports sphere mapping which requires a circular texture map equivalent to an image taken with a fisheye lens Sphere Mapping Example 5 Sphere Mapping Limitations Visual artifacts are common Sphere mapping is view dependent Acquisition of images non-trivial Need fisheye lens Or render from fisheye lens Cube maps are easier to acquire Or render Acquiring a Sphere Map…. Take a picture of a shiny sphere in a real environment Or render the environment into a texture (see next slide) Why View Dependent? Conceptually a sphere map is generated like ray-tracing Records reflection under orthographic projection From a given view point What is a drawback of this? Cube Map Cube mapping takes a different approach…. Imagine an object is in a box …and you can see the environment through that box 9 Forming a Cube Map Reflection Mapping How Does WebGL Index into Cube Map? •To access the cube map you compute R = 2(N·V)N-V •Then, in your shader vec4 texColor = textureCube(texMap, R); V R •How does WebGL
    [Show full text]
  • Texture Mapping Effects
    CS 543 Computer Graphics Texture Mapping Effects by Cliff Lindsay “Top Ten List” Courtesy of David Letterman’s Late Show and CBS Talk Format List of Texture Mapping Effects from Good to Spectacular (my biased opinion): Highlights: . Define Each Effect . Describe Each Effect Briefly: Theory and Practice. Talk about how each effect extends the idea of general Texture Mapping (previous talk) including Pros and Cons. Demos of selected Texture Mapping Effects 1 Texture Mapping Effect #10 Light Mapping Main idea: Static diffuse lighting contribution for a surface can be captured in a texture and blended with another texture representing surface detail. Highlights: . Eliminate lighting calculation overhead . Light maps are low resolution . Light maps can be applied to multiple textures * = [Images courtesy of flipcode.com] Light Mapping Below is a night scene of a castle. No lighting calculation is being performed at all in the scene. Left: No Light Map applied Right: Light Map applied [Images courtesy of www.gamasutra.com] 2 Texture Mapping Effect #9 Non-Photorealistic Rendering Main idea: Recreating an environment that is focused on depicting a style or communicating a motif as effectively as possible. This is in contrast to Photorealistic which tries to create as real a scene as possible. High lights of NPR: . Toon Shading . Artistic styles (ink, water color, etc.) . Perceptual rendering [Robo Model with and without Toon Shading, Image courtesy of Michael Arias] Non-Photorealistic Rendering Non-Photorealistic Rendering Simple Example: Black
    [Show full text]
  • Real-Time Rendering (Echtzeitgraphik)
    Real-Time Rendering (Echtzeitgraphik) Dr. Michael Wimmer [email protected] Shading and Lighting Effects Overview Environment mapping Cube mapping Sphere mapping Dual-paraboloid mapping Reflections, Refractions, Speculars, Diffuse (Irradiance) mapping Normal mapping Parallax normal mapping Advanced Methods Vienna University of Technology 3 Environment Mapping Main idea: fake reflections using simple textures Vienna University of Technology 4 Environment Mapping Assumption: index envmap via orientation Reflection vector or any other similar lookup! Ignore (reflection) position! True if: reflecting object shrunk to a single point OR: environment infinitely far away Eye not very good at discovering the fake Environment Map Viewpoint Vienna University of Technology 5 Environment Mapping Can be an “Effect” Usually means: “fake reflection” Can be a “Technique” (i.e., GPU feature) Then it means: “2D texture indexed by a 3D orientation” Usually the index vector is the reflection vector But can be anything else that’s suitable! Vienna University of Technology 6 Environment Mapping Uses texture coordinate generation, multitexturing, new texture targets… Main task: Map all 3D orientations to a 2D texture Independent of application to reflections Sphere Cube Dual paraboloid Top top Top Left Front Right Left Front Right Back left front right Bottom Bottom Back bottom Vienna University of Technology 7 Cube Mapping OpenGL texture targets Top Left Front Right Back Bottom glTexImage2D( GL_TEXTURE_CUBE_MAP_POSITIVE_X, 0, GL_RGB8, w, h, 0, GL_RGB, GL_UNSIGNED_BYTE,
    [Show full text]
  • Environment Mapping Good for ? with the Help of Environment Mapping, an Object Can Reflect the Environment
    Environment Mapping good for ? With the help of environment mapping, an object can reflect the environment. For that Simone Kriglstein texture mapping can be used. But some problems Günter Wallner are occurring. The problem how the textures are saved must be solved (i.e. to save memory). The second problem is that the calculation of mapping Abstract the 2-dimensional to 3-dimensional coordinates must be possible in a short time, so that these In this paper environment mapping is presented. techniques can be used in interactive applications. First we will discuss environment mapping in For parameterization three different kinds are general and the methods of parameterization like, existing. The most famous methods are spherical, sphere -, cubic –and parabolic maps. For sphere, cube and parabolic maps. We will discuss each of parabolic and cubic maps the way of indexing is the methods mentioned above and enumerate the shown. Then ways of prefiltering of environment advantages and disadvantages of those maps are shown. In detail we present how this can parameterizations. Since there are different kinds of be done with the Phong reflection model and how surfaces (wood, plastic,...) with different kinds of the Fresnel term can be used. In addition reflection properties (Figure 1.2 shows a very good environment mapping with the help of BRDF´s is example of reflection), these properties should be presented. Also environment mapped bump taken into account when generating an environment mapping (EMBM) will be discussed. In this chapter map. The reflection properties can be divided into we discuss mainly how the environment is mapped three parameters: diffuse, glossy and mirror.
    [Show full text]
  • Texture Mapping
    Computer Graphics Texture Mapping Teacher: A.prof. Chengying Gao(高成英) E-mail: [email protected] School of Data and Computer Science Basic Conception of Texture Mapping Computer Graphics 2 Limitations Computer Graphics 3 Limitations • Even though the graphics card can display up to ten million polygons per second,It's difficult to simulate all the phenomenon in nature. • Cloud • Grass • Leaf • Landforms • Hair • Fire and Water Computer Graphics 4 The Importance of Surface Texture Computer Graphics 5 The Quest for Visual Realism Computer Graphics 6 Texturing Example • SkyBox Computer Graphics 7 Texturing Example Computer Graphics 8 Model of Orange • Consider the method to create model of orange (or some of other fruits). • Coloring orange in a simple sphere? • Not reality • Instead more complicate shape of sphere? • Too many polygons to display the dimples in the surface Computer Graphics 9 Why Texture Mapping? • Texture is variation in the surface attributes • like color, surface normals, specularity, transparency, surface displacement etc. • Computer generated images look more realistic if they are able to capture these complex details • It is difficult to represent these details using geometric modeling because they heavily increase computational requirements • Texture mapping is an effective method of “faking” surface details at a relatively low cost Computer Graphics 10 What is texture mapping • Texture mapping is the process of transforming a texture on to a surface of a 3D object. • It is like mapping a function on to a surface in 3D • the domain of the function could be 1D, 2D or 3D • the function could be represented by either an array or it could be an algebraic function.
    [Show full text]
  • Cube-To-Sphere Projections for Procedural Texturing and Beyond
    Journal of Computer Graphics Techniques Vol. 7, No. 2, 2018 http://jcgt.org Cube-to-sphere Projections for Procedural Texturing and Beyond Matt Zucker and Yosuke Higashi Swarthmore College (a) (b) (c) (d) Figure 1. Real-time shader illustrating stratified sampling of the sphere. (a) jittered uniform grid on cube; (b) nonlinear warp of each face; (c) projection to sphere via normalization; (d) resulting Voronoi diagram, generated in constant time per fragment. Abstract Motivated by efficient GPU procedural texturing of the sphere, we describe several approxi- mately equal-area cube-to-sphere projections. The projections not only provide low-distortion UV mapping, but also enable efficient generation of jittered point sets with O(1) nearest- neighbor lookup. We provide GLSL implementations of the projections with several real-time procedural texturing examples. Our numerical results summarize the various methods’ abil- ity to preserve projected areas as well as their performance on both integrated and discrete GPUs. More broadly, the overall cube-to-sphere approach provides an underexplored avenue for adopting existing 2D grid-based methods to the sphere. As an example, we showcase fast Poisson disk sampling. 1 ISSN 2331-7418 Journal of Computer Graphics Techniques Vol. 7, No. 2, 2018 Cube-to-sphere Projections for Procedural Texturing and Beyond http://jcgt.org 1. Introduction Spheres are ubiquitous primitives in computer graphics, used to render everything from molecules to planets. Sampling and tessellating the sphere is fundamental to texturing and modeling these common objects. Most users of modern graphics APIs are familiar with cube mapping [Greene 1986], a technique that is commonly used to map between 3D direction vectors and 2D textures tiling the surface of a cube.
    [Show full text]
  • 15-462 Project 2: Texture Mapping and Shaders
    15-462 Project 2: Texture Mapping and Shaders Release Date: Tuesday, February 10, 2009 Due Date, Tuesday, February 24, 2009 at 23:59:59 1 Overview In this project, you will learn to do texture mapping in OpenGL and implement bump mapping, environment mapping and Fresnel effect in OpenGL Shading Language (GLSL). Before you start, you will need to download the staff code from the course website and update your project 1 code according to section4 of this document. Starter Code: http://www.cs.cmu.edu/~15462/proj/02/p2.tar.gz You may also find the following documents very useful for GLSL programming: GLSL Quick Reference Guide: http://www.opengl.org/sdk/libs/OpenSceneGraph/glsl_quickref.pdf GLSL Specification: http://www.opengl.org/registry/doc/GLSLangSpec.Full.1.20.8.pdf OpenGL Reference Pages: http://www.opengl.org/sdk/docs/man/ 2 Submission Process Your handin directory may be found at /afs/cs.cmu.edu/academic/class/15462-s09-users/andrewid/p2/. You should submit the entire contents of the handout, your modified files, and any screenshots in this directory. Regardless of what machine you use to code your assignment, it must com- pile and run correctly on the machines in the Wean 5336 cluster. There are a lot of students in the course and only 25 machines, so you probably don't want to wait until the last minute to test it. To test your code, we will simply cd into the directory, then run make clean; make. Therefore, your code should should be placed in the root directory un- 1 compressed (i.e.
    [Show full text]
  • CG08-Texturing.Pdf
    Computer Graphics - Texturing - Philipp Slusallek Texture • Textures modify the input for shading computations – Either via (painted) images textures or procedural functions • Example texture maps for – Reflectance, normals, shadow reflections, … 2 Definition: Textures • Texture maps texture coordinates to shading values – Input: 1D/2D/3D/4D texture coordinates • Explicitly given or derived via other data (e.g. position, direction, …) – Output: Scalar or vector value • Modified values in shading computations – Reflectance • Changes the diffuse or specular reflection coefficient (푘푑, 푘푠) – Geometry and Normal (important for lighting) • Displacement mapping 푃′ = 푃 + Δ푃 • Normal mapping 푁′ = 푁 + Δ푁 • Bump mapping 푁′ = 푁(푃 + 푡푁) – Opacity • Modulating transparency (e.g. for fences in games) – Illumination • Light maps, environment mapping, reflection mapping – And anything else … IMAGE TEXTURES 4 Wrap Mode • Texture Coordinates 0, 4 v 4, 4 – (u, v) in [0, 1] x [0, 1] ? ? ? ? • What if? – (u, v) not in unit square? ? ? ? ? ? ? ? ? 0, 1 ? ? ? u 0, 0 1, 0 4, 0 Wrap Mode • Repeat 0, 4 v 4, 4 • Fractional Coordinates – 푡푢 = 푢 − 푢 – 푡푣 = 푣 − 푣 u 0, 0 4, 0 Wrap Mode • Mirror 0, 4 v 4, 4 • Fractional Coordinates – 푡푢 = 푢 − 푢 – 푡푣 = 푣 − 푣 • Lattice Coordinates – 푙푢 = 푢 – 푙푣 = 푣 • Mirror if Odd – if (l_u % 2 == 1) t_u = 1 - t_u u – if (l_v % 2 == 1) t_v = 1 - t_v 0, 0 4, 0 Wrap Mode • Clamp 0, 4 v 4, 4 • Clamp u to [0, 1] if (u < 0) tu = 0; else if (u > 1) tu = 1; else tu = u; • Clamp v to [0, 1] if (v < 0) tv = 0; else if (v > 1) tv = 1; else tv =
    [Show full text]
  • Texture Mapping
    Texture Mapping University of California Riverside Limits of geometric modeling Although modern GPUs can render millions of triangles/sec, that's not enough sometimes. Texture mapping for detail This image contains 8 polygons! Texture mapping comparison no texture with texture Pixar - Toy Story Other uses of textures. Light maps Shadow maps Environment maps Bump maps Opacity maps Animation Lookup reflectances in image Image source: [1, 2] Texture mapping in the pipeline vertex input vertex shader Geometry and pixels have separate tessellation paths through pipeline geometry shader Textures applied in fragment shader post vertex processing End of pipeline Efficient since relatively few polygons primitive assembly get past clipper rasterization fragment shader per-sample operations uv Mapping (u0; v0) 2D texture is parameterized by (u; v) (u1; v1) Assign polygon vertices texture coordinates Interpolate within polygon (u2; v2) Texturing triangles Store (u; v) at each vertex Interpolate inside triangles using barycentric coordinates Texture Space Object Space v 1, 1 (u,v) = (0.2, 0.8) 0, 1 A a c (0.4, 0.2) b B C 0, 0 1, 0 u (0.8, 0.4) Texturing triangles Store (u; v) at each vertex Interpolate inside triangles using barycentric coordinates p(β; γ) = pa + β(pb − pa) + γ(pc − pa) u(β; γ) = ua + β(ub − ua) + γ(uc − ua) v(β; γ) = va + β(vb − va) + γ(vc − va) Texture mapping Point sampling Map back to texture image and use the nearest texel Aliasing Point sampling textures can lead to aliasing artifacts Magnification and minification Minification Magnification
    [Show full text]