Texturing Theory. Overview. All it takes is for the rendered image to look right. -Jim Blinn 11/10/2018

Transcription

1 References: Real-Time Rendering 3 rd Edition Chapter 6 Texturing Theory All it takes is for the rendered image to look right. -Jim Blinn Overview Introduction The Texturing Pipeline Example The Projector Function The Corresponder Function Texture Values Image Texturing Magnification Minification Cube Maps Alpha Mapping Texturing in WorldViz Vizard Texture Animation Texturing in 3D Studio Max 1

2 Introduction Texture A Component of a Material Textures can fill a variety of roles, the most typical being the diffuse component of an object Introduction Texture the look and feel of an object modifying surface appearance via an image or function Texturing a method to efficiently model a surface s properties 2

3 Introduction Texture Mapping binds images to polygons to increase realism without drastically increasing detail After an image is loaded and used it is referred to as a texture map The individual pixels of an image are referred to as texels to distinguish them from screen pixels Introduction Texturing adds detail with little expense thanks to hardware 3

4 Introduction Textures can be 1, 2 or 3 dimensions ( technically, even 4 ) Gradient Image Marble, Leather, Mathematical Functions Introduction 4D Texture 4

5 Introduction Mapped through the use of Texture Coordinates Texture coordinate range: [0.0f -> 1.0f) Texture coordinates are denoted as: (U, V, W) or (S, T, R) 3D Polygon UV Coordinates Texturing Pipeline The process of apply textures to an object is a pipeline Through the use of several functions, we arrive at the final color value sampled from a texel 1. Use the model s local vertex positions 2. Apply a projector function to obtain parameter-space values. Parameter space values are used to access the correct piece of a texture. This process referred to as mapping 5

6 Texturing Pipeline 3. Corresponder functions are used to transform the parameter-space values to texture space (image space) and specify what to do outside the [0,1) range The values can be obtained from the texture (array indices into a pixel map 4. A value transform function transform the texel s value if needed. Additional step if values need to be adjusted Texturing Pipeline - Example Get the (x,y,z) position of the point (local coordinates) Apply projector function: (x,y,z) -> (u,v) Values are mapped: (-2.3x, 7.1y, 88.2z) -> (0.32u,0.29v) (0.32u,0.29v) are now parameter space coordinates 6

7 Texturing Pipeline - Example The corresponder function converts the [0->1) parameter space coords between 0 and image size Multiply the [0,1) value by image size Image size is a power of 2 and square (256x256) The values become (81.92u, 74.24v) Texturing Pipeline - Example Drop the fractional component (81u, 74v) Sample the pixel at (81u,74v) Get the color (0.9R, 0.8G, 0.7B) A transform function could be used if it was too dark Scale up the color by 1.1: (0.99R, 0.88G, 0.77B) 7

8 Projector Function Real-time graphics usually have the projector function applied during asset creation stage The projection information is stored per vertex as a texture coordinate (our UV coordinates) You will be assigning your model s UV coordinates inside of Maya using the UV Projections Projector Function You do not need to just use the projector functions provided, you can create your own skins that appear heavily distorted and organic 8

9 Projector Function Examples of Basic Projector Functions: Spherical Cylindrical Planar This will be further explained inside of 3D Studio Max Projector Function Multiple types of projectors were used to unwrap this hand 9

10 Projector Function Projecting a curved /organic surface is not without problems Projector Function Look at all the breaking /cutting to unfold an orange 10

11 Projector Function There is no stress/strain when stretching UV coords Instead of breaking we will get distortions Manually insert cuts to reduce distortions View the distortions by applying a pattern across the surface (checkerboard) Stretching can be created easiest by selecting a vertex with smooth select and displacing the points Utilizing various techniques can get you less distortion, but may include many cuts Projector Function - Unfolding 11

12 Projector Function - Cutting Projector Function - Layout 12

13 Projector Function Corresponder Function The corresponder function converts the (u,v) parameter into texture space (where we get the actual pixel value) Provides flexibility when applying textures Allows for matrix transformations to translate, rotate, scale, shear and project the texture on the surface Most importantly: Determines how the texture is sampled outside the [0,1) UV coordinate range 13

14 Corresponder Function We can modify our texture coordinates in Maya using the Hypershade and selecting the 2D Placement node Corresponder Function A corresponder function can be applied to animate textures across a surface 14

15 Corresponder Function Corresponder functions can control how a texture is applied There are several wrapping modes: Wrap / repeat / tile Mirror Clamp / clamp to edge Border / clamp to border Corresponder Function You can specify the wrap mode in Unity through the inspector You can access the wrap settings through code using: Texture.wrapMode Texture.wrapModeU Texture.wrapModeV Texture.wrapModeW And using the enumeration: TextureWrapMode.Repeat TextureWrapMode.Clamp TextureWrapMode.Mirror TextureWrapMode.MirrorOnce 15

16 Corresponder Function Repeating textures can add more visual detail without expense However, anymore than 3 repetitions usually becomes noticeable Corresponder Function Solutions: Combine multiple textures either through a shader or Use Wang tiles that share the same edge yet have different inner values 16

17 Texture Values The corresponder coordinates are used to get the texture value Images: Procedural textures: the value is looked up a functional computation Textures formats vary: RGB, RGBA, BGR, grayscale, various byte sizes 17

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19 Image Texturing Typically, an image is 2 m x 2 n with a max size varying between If we sample a square, and the number of pixels sampled for the screen is roughly equal to the number of pixels in the texture, things appear fine If the projected square covers a larger number of pixels, more than what is available in our texture, what happens? (Magnification) If our projection covers a small number of pixels, what happens? (Minification) Magnification When the screen samples more texture than there is resolution Nearest Neighbor uses the nearby value Bilinear uses the closest 4 pixels and averages the result Cubic utilizes multiple values 4 to 5 pixels out 19

20 Magnification When the screen samples more texture than there is resolution Nearest Neighbor uses the nearby value Bilinear uses the closest 4 pixels and averages the result Cubic utilizes multiple values 4 to 5 pixels out x4 5x5 Minification What value do we use when possibly hundreds overlap on the same pixel? Nearest Neighbor Utilize the closest texel value as seen in the top image Bilinear Interpolation As with magnification, use the 4 closest texels Summed Area Tabled (We will not discuss these) Bottom image 20

21 Minification - Mipmaps Mipmaps (multum in parvo many things in a small place ) The most popular method for minification The zero level texture is continually downsampled by ¼ until it reaches 1x1 Mipmaps are the reason textures are usually required to be 2 x Minification - Mipmaps Example mipmap levels created using the NVIDIA Photoshop Plugin 21

22 Minification - Mipmaps Unity will create mipmaps for you automatically, however you may end up with blending artifacts based on the filtering used Minification Anisotropic filtering allows for additional samples to be taken along the vertical axis 22

23 Minification Anisotropic filtering allows for additional samples to be taken along the vertical axis Can be set on: Texture.anisoLevel Ranges between values of 1 and 9, higher values will impact performance Minification Great for making ground planes look better 0 Samples 10 Samples 23

24 Cube Maps Cube maps provide environmental mapping of a scene Images for the entire scene are taken or created A vector determines which cube to sample Pre-computed cube maps can fake environmental reflections Cube Maps You can create your own environmental maps inside Maya. Create a camera system composed of 6 cameras, and make sure their FOVs overlap. 24

25 Environmental Reflections in Unity Environmental reflections are now handled by using Reflection Probes These can either pre-render the scene or do it in real time Only objects that are marked Reflection Probe Static will show up in the rendered image Lightbaking No Textures 25

26 Lightbaking Gloomy Lightbake Lightbaking Colored Lightbake 26