三維繪圖程式設計 3D Graphics Programming Design 第七章基礎材質張貼技術嘉大資工系盧天麒

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1 三維繪圖程式設計 3D Graphics Programming Design 第七章基礎材質張貼技術嘉大資工系盧天麒 1

2 In this chapter, you will learn The basics of texture mapping Texture coordinates Texture objects and texture binding Texture specification with 2D Texture filtering Mipmaps and automatic mipmap generation Texture parameters, wrap modes, and level of detail Textured terrain 2

3 Introduction You can create photo-realistic worlds with texture mapping The object being viewed on the screen are real 3

4 An Overview of Texture Mapping Texture mapping allows you Attach images to polygons to provide more realistic graphics The first step in bringing the realism Texture maps Are composed of rectangular arrays of data Each element of these arrays is called a texel 4

5 An Overview of Texture Mapping Texture maps can be mapped to nonrectangular objects Spheres, cylinders, and other 3D object models 5

6 An Overview of Texture Mapping One-dimensional textures have a width and a height equal to only 1 pixel The two-dimensional texture has both a width and a height Three-dimensional textures have a width, height, and depth Called volume textures 6

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8 Texture Coordinates The lower-left corner of a texture is given the coordinates (0, 0) The upper-right corner of a texture is given the coordinates (1, 1) Texture coordinates for 2D textures are given the notation (s, t) s and t are equal to a value from 0 to 1 8

9 Texture Coordinates 1D, 3D, and 4D texture coordinates are given the notation (s), (s, t, r), and (s, t, r, q), respectively 9

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11 Texture Coordinates Texture coordinates are specified with the gltexcoord( ) function As an example, you would set a 2D texture coordinate to (0.2, 0.4) gltexcoord2f(0.2, 0.4); 11

12 Texture Coordinates The following code sets the 2D texture coordinate for a polygon: glbegin(gl_polygon); gltexcoord2f(0.0f, 0.0f); glvertex3f(-0.5f, 0.5f, 0.5f); // lower left gltexcoord2f(1.0f, 0.0f); glvertex3f(0.5f, 0.5f, 0.5f); // lower right gltexcoord2f(1.0f, 1.0f); glvertex3f(-0.5f, 0.5f, -0.5f); // upper right gltexcoord2f(0.0f, 1.0f); glvertex3f(-0.5f, 0.5f, -0.5f); // upper left glend(); 12

13 Using the Texture Map Once you have your texture image loaded into memory Specify it as a texture map with OpenGL Generate what is called a texture object Store information about the texture Including the image data and how it is to be applied 13

14 Using the Texture Map Texturing is enabled and disabled through the use of the glenable( ) and gldisable( ) functions The constants GL_TEXTURE_1D, GL_TEXTURE_2D, GL_TEXTURE_3D, or GL_TEXTURE_CUBE_MAP 14

15 Texture Objects Texture objects are internal data structures that hold texture data and parameters Each texture object has state associated with it that is unique to that texture Using unique identifiers for texture objects 15

16 Texture Objects OpenGL provides the glgentextures( ) function void glgentextures(glsizei n, GLuint *textures); This function returns n previously unused objects identifiers in the textures array unsigned int textureobjects[3]; glgentextures(3, textureobjects); 16

17 Texture Binding The first time you bind a texture object, it acquires a new set of states with initial values You can then modify to suit your needs The glbindtexture( ) function performs the binding operation 17

18 Texture Binding void glbindtexture(glenum target, GLuint texture); target must be the desired target of the bound textures: GL_TEXTURE_1D, GL_TEXTURE_2D, GL_TEXTURE_3D, or GL_TEXTURE_CUBE_MAP texture is simply the identifier for the texture object you want to bind 18

19 Texture Binding For example glbindtexture(gl_texture_2d, textureobject[0]); While a texture object is bound to a target, OpenGL texturing operations on that target affect the texture object 19

20 Texture Binding Examine this code glbindtexture(gl_texture_2d, textureobjects[0]); // all texture operations using GL_TEXTURE_2D now affect textureobjects[0] glbindtexture(gl_texture_3d, textureobjects[1]); // all texture operations using GL_TEXTURE_2D still affect textureobjects[0] // all texture operations using GL_TEXTURE_3D now affect textureobjects[1] glbindtexture(gl_texture_2d, textureobjects[2]); // all texture operations using GL_TEXTURE_3D still affect textureobjects[1] // all texture operations using GL_TEXTURE_2D now affect textureobjects[2] 20

21 Deleting Texture Objects Prevent resource leaks you need to delete them Texture objects are deleted by calling the gldeletetextures( ) function void gldeletetextures(glsizei n, GLuint *textures); The textures parameter contains n texture object identifiers to be deleted 21

22 Resident Textures All video cards have a limited amount of memory Determine whether a texture object is currently a part of the working set of texture objects 22

23 Resident Textures Function Glboolean glaretexturesresident(glsizei n, GLuint *textures, GLboolean *residences); This function returns GL_TRUE if all of the texture objects identified in textures are resident in the working set If at least one of the textures identified in textures is not resident in the working set, the function returns GL_FALSE 23

24 Specifying Textures OpenGL provides three main functions for specifying a texture: glteximage1d( ), glteximage2d( ), glteximage3d( ) 24

25 Specifies 2D Texture Image void glteximage2d( GLenum target, GLint level, GLint internalformat, GLsizei width, GLsizei height, GLint border, GLenum format, GLenum type, const GLvoid *pixels ); 25

26 Specifies 2D Texture Image Specifies a 2D texture image ary/en-us/opengl/glfunc03_16jo.asp target: Must be GL_TEXTURE_2D level: level-of-detail level. It must be 0 if you don t want to use mip-map. internalformat: GL_RGBA and many others Width / height: image width / height 26

27 Specifies 2D Texture Image internalformat The number of color components in the texture Must be 1, 2, 3, or 4, or one of the following symbolic constants: GL_ALPHA, GL_ALPHA4, GL_ALPHA8, GL_ALPHA12, GL_ALPHA16, GL_LUMINANCE, GL_LUMINANCE4, GL_LUMINANCE8, GL_LUMINANCE12, GL_LUMINANCE16, GL_LUMINANCE_ALPHA, GL_LUMINANCE4_ALPHA4, GL_LUMINANCE6_ALPHA2, GL_LUMINANCE8_ALPHA8, GL_LUMINANCE12_ALPHA4, GL_LUMINANCE12_ALPHA12, GL_LUMINANCE16_ALPHA16, GL_INTENSITY, GL_INTENSITY4, GL_INTENSITY8, GL_INTENSITY12, GL_INTENSITY16, GL_R3_G3_B2, GL_RGB, GL_RGB4, GL_RGB5, GL_RGB8, GL_RGB10, GL_RGB12, GL_RGB16, GL_RGBA, GL_RGBA2, GL_RGBA4, GL_RGB5_A1, GL_RGBA8, GL_RGB10_A2, GL_RGBA12, or GL_RGBA16. 27

28 Specifies 2D Texture Image Border: 0 or 1 0 : no border, image width & height must be power of 2. 1 : use border, image width & height must be power of 2 plus 2. 28

29 Specifies 2D Texture Image format: format of the image data GL_RGB, GL_RGBA, and many others type: data type of the image data pixel: A pointer to the image data in memory. (Hint: the BMP file you have loaded ) 29

30 Specifies 2D Texture Image Texture pixel format 30

31 Specifies 2D Texture Image Texture data type 31

32 Specifies 2D Texture Image The data type GL_UNSIGNED_BYTE_3_3_2 with the format being GL_RGB Red component is in bits 5-7 Green component is in bits 2-4 Blue component is in bits 0-1 GL_UNSIGNED_BYTE_3_3_2 type Red Green Blue

33 Specifies 2D Texture Image As an example, you have loaded an RGBA image into the variable texturedata that has a width and height of texturewidth and textureheight glteximage2d(gl_texture_2d, 0, GL_RGBA, texturewidth, textureheight, 0, GL_RGBA, GL_UNSIGNED_BYTE, texturedata); After this function is called, the texture is load and ready to use 33

34 Texture Filtering Texture mapping a polygon is the act of mapping from texture image space to frame buffer image space Texture filtering Tell OpenGL how it should map the texels to pixels when calculating the final image 34

35 Texture Filtering In texture filtering Magnification When a screen pixel represents a small portion of a texel Minification When a pixel contains a number of texels 35

36 Texture Filtering You can tell OpenGL how to handle both of these filtering cases with the gltexparameter( ) function 36

37 Texture Filtering void gltexparameter{if}(glenum target, Glenum pname, T param); void gltexparameter{if}v(glenum target, Glenum pname, T params); The value target parameter refers to the texture target and can be equal to GL_TEXTURE_1D, GL_TEXTURE_2D, GL_TEXTURE_3D, or GL_TEXTURE_CUBR_MAP The pname GL_TEXTURE_MAG_FILTER, GL_TEXTURE_MIN_FILTER 37

38 Texture Filtering When specifying the GL_TEXTURE_MAG_FILTER, the param may be equal to either GL_NEAREST or GL_LINEAR GL_NEAREST Tell OpenGL to use the texel nearest to the center of the pixel being rendered GL_LINEAR Tell OpenGL to use the weighted average of the four texels closest to the center of the pixel being rendered 38

39 Texture Filtering When specifying GL_TEXTURE_MIN_FILTER 39

40 Texture Filtering By default, the magnification filter is set to GL_LINEAR The minification is set to GL_NEAREST_MIPMAP_LINEAR 40

41 Basic Texture Example A basic example that applies a texture to two polygons This example moves two polygons along the z-axis to show the minification and magnification function texture filter settings Affect the visual quality of a texture map 41

42 Basic Texture Example 42

43 Basic Texture Example The polygon on the left uses GL_LINEAR for both minification and magnification Resulting in a smooth transition The polygon on the right uses GL_LINEAR for minification and GL_NEAREST for magnification The texture s visual quality changes slightly when it passes through the threshold for OpenGL to switch from minification to magnification 43

44 Basic Texture Example In the init( ) method, 6 steps: We first enable 2D texturing Load the texture image data using the CTargaImage class We then get an unused texture object through glgentextures( ) Bind the texture object Specify the minification and magnification for the texture object as GL_LINEAR Specify the texture with glteximage2d( ) We repeat the process for the second texture object 44

45 bool CGfxOpenGL::Init() { glclearcolor(0.0, 0.0, 0.0, 0.0); // enable 2D texturing glenable(gl_texture_2d); m_textureone = new CTargaImage; // load texture image data if (!m_textureone->load("rock.tga")) return false; // retrieve "unused" texture object glgentextures(1, &m_textureobjectone); // bind the texture object glbindtexture(gl_texture_2d, m_textureobjectone); // minimum required to set the min and mag texture filters gltexparameteri(gl_texture_2d, GL_TEXTURE_MAG_FILTER, GL_LINEAR); gltexparameteri(gl_texture_2d, GL_TEXTURE_MIN_FILTER, GL_LINEAR); // now that the texture object is bound, specify a texture for it glteximage2d(gl_texture_2d, 0, GL_RGB, m_textureone->getwidth(), m_textureone->getheight(), 0, GL_RGB, GL_UNSIGNED_BYTE, m_textureone->getimage()); // create the second texture object glgentextures(1, &m_textureobjecttwo); glbindtexture(gl_texture_2d, m_textureobjecttwo); gltexparameteri(gl_texture_2d, GL_TEXTURE_MAG_FILTER, GL_NEAREST); gltexparameteri(gl_texture_2d, GL_TEXTURE_MIN_FILTER, GL_LINEAR); glteximage2d(gl_texture_2d, 0, GL_RGB, m_textureone->getwidth(), m_textureone->getheight(), 0, GL_RGB, GL_UNSIGNED_BYTE, m_textureone->getimage()); // initialize movement variables m_zpos = -5.0f; m_zmovenegative = true; return true; } 45

46 Basic Texture Example In DrawPlane( ), we are specifying the texture coordinates and drawing the vertices of the texture polygon void CGfxOpenGL::DrawPlane() { glbegin(gl_triangle_strip); gltexcoord2f(2.0, 0.0); glvertex3f(2.0, -2.0, -2.0); gltexcoord2f(0.0, 0.0); glvertex3f(-2.0, -2.0, -2.0); gltexcoord2f(2.0, 2.0); glvertex3f(2.0, -2.0, 2.0); gltexcoord2f(0.0, 2.0); glvertex3f(-2.0, -2.0, 2.0); glend(); } 46

47 Build Mip-Maps (1/4) Refer to a texture that is composed of many different levels Each level has dimensions that are half of the previous one The GLU library provides the glubuild2dmipmaps( ) and glubuild1dmipmaps( ) functions to build mipmaps 47

48 Build Mip-Maps (2/4) int glubuild2dmipmaps( GLenum target, GLint components, GLint width, GLint height, GLenum format, GLenum type, const void *data ); url=/library/en-us/opengl/glufnc01_406r.asp 48

49 Build Mip-Maps (3/4) target : Must be GL_TEXTURE_2D components :The number of color components in the texture. Must be 1, 2, 3, or 4 width, height :width / height of image. format : GL_RGB, GL_RGBA and many others type :The data type for data data :A pointer to the image data in memory glubuild2dmipmaps(gl_texture_2d, GL_RGB, 64, 64, GL_RGB, GL_UNSIGNED_BYTE, teximage0); 49

50 Build Mip-Maps (4/4) without mip-map with mip-map 50

51 Texture Parameter gltexparameter{if}(glenum target, GLenum pname, GLfloat param ) Set texture parameters url=/library/en-us/opengl/glfunc03_9upe.asp target: GL_TEXTURE_1D, GL_TEXTURE_2D pname / param: see next page 51

52 Texture Parameter 52

53 Texture Parameter Wrap Clamp both S, T Repeat both S, T Repeat T but Clamp S 53

54 Texture Parameter MAG filter When the pixel being textured maps to an area less than or equal to one texture element MIN filter When the pixel being textured maps to an area greater than one texture element 54

55 Texture Parameter GL_NEAREST GL_LINEAR pixel texel Get average color... GL_NEAREST_MIPMAP_XXXXXX Find the most closely match mipmap GL_LINEAR_MIPMAP_XXXXXXX Find the most 2 closely match mipmap and get average 55

56 Textured Terrain A heightfield terrain is a virtual representation of a landscape Its data points are a 2D set of evenly spaced height values 56

57 Building the Mesh You will be determining the height values by loading a 32X32 grayscale Targa image into memory We will be using a grayscale image, the color values and efficiently the height values will range from 0 to

58 Building the Mesh After loading the height values into an array in memory You will have a set of data points that represent the height of the terrain 58

59 Building the Mesh You need to determine the distance between each height vertex Called map scale You will use the map scale to programmatically increase or decrease the actual width and height of the terrain in world units 59

60 Building the Mesh Skybox Is a large cube whose inside faces are textured with images representing the distant horizon Provide a good, simple way to enhance the environment of an outdoor graphics scene 60

61 Building the Mesh The position of the camera is used as the origin of the skybox We added mouse input control for the camera You can rotate and set the height of the camera with the mouse DrawTerrain( ) function 61

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64 Summary You learned the basics of the texture mapping You have learned about Texture mapping allows you to attach images to polygons to create realistic objects The first time you bind a texture The texture object acquires a new state with initial values You can then modify to suit your needs After that, binding the effectively selects the texture 64

65 References Dave Astle and Kevin Hawkins, Beginning OpenGL Game Programming, 1st Edition, Course Technology PTR,