Chapter 6 Texture Mapping

Transcription

1 Chapter 6 Texture Mapping Understand what texture mapping can add to your scene Specifying the texture map and how its coordinates relate to those of the objects in your scene Control how a texture image is filtered as it's applied to a fragment Specify how the color values in the image combine with those of the fragment to which it's being applied Use automatic texture coordinate generation to produce effects like contour maps and environment maps 1

2 Textures and Its Applications Textures are simply rectangular arrays of data The individual values in a texture array are often called texels General applications: simulating materials( 以貼圖代替繪橘子皮, 壁紙, 磁磚, 和木紋等 ) reducing geometric complexity image warping Reflections( 如在茶壺上畫周遭環境的反射影像 ) 2

3 Texture Mapping y z x geometry t image s 3 screen

4 Texture Mapping and the OpenGL Pipeline Images and geometry flow through separate pipelines that join at the rasterizer complex textures do not affect geometric complexity vertices image geometry pipeline pixel pipeline rasterizer 4

5 5 Texture Exampletexture.bat

6 Steps in Texture Mapping 1. Specify the texture ( 例如載入或自訂貼圖陣列 ) 2. Indicate how the texture is to be applied to each pixel 3. Enable texture mapping 4. Draw the scene, supplying both texture and geometric coordinates Redbook Samples\CHECKER.EXE 6

7 Specify Texture Image Define a texture image from an array of texels glteximage2d(target, level, components, w, h, border, format, type, *texels); Ex: #define ImageW 64 #define ImageH 64 GLubyte Image[ImageW][ImageH][3]; void makecheckimage(void) { // 建立一個陣列 Image[][][3], 系統尚不知此陣列為一張貼圖 int i, j, c; for (i = 0; i < ImageW; i++) { for (j = 0; j < ImageH; j++) { c = ((((i&0x8)==0)^((j&0x8)==0)))*255 Image[i][j][0] = (GLubyte) c; ;//if i,j=0~7, c = [(0==0)^(0==0)]*255 Image[i][j][1] = (GLubyte) c; // c = [0^0]*255 = 0 Image[i][j][2] = (GLubyte) c; }//end of j }//end of i }// end of makecheckimage i=0~7, j=0~7,c=0 i=8~15, j=0~7,c=255 // 將上列所定義之陣列指定為一張 2 維貼圖 c=(0~255) glteximage2d (GL_TEXTURE_2D, 0, 3, ImageW, ImageH, 0, GL_RGB, GL_UNSIGNED_BYTE, &Image[0][0][0]); target, level, components, w, h, border, format, datatype, *texels (target 2d texture, level of detail: 0 (normal), 3 components (red, green, blue), x size of image, y size of image, border 0 (normal), rgb color data, unsigned byte data, the data itself) Note: dimensions of image must be powers of 2 7

8 Another Method of Applying Textures specify textures in texture objects( 載入貼圖影像, 產生貼圖名稱, 並建立二者之間的連結 ) set texture filter set texture function set texture wrap mode set optional perspective correction hint bind texture object enable texturing Select a specified texture name and supply texture coordinates for vertex 8

9 LOAD BITMAPS #include <GL/glaux.h> // Header File For The Glaux Library AUX_RGBImageRec *LoadBMP(char *Filename) // Loads A Bitmap Image { FILE *File=NULL; // Define File Handle if (!Filename) return NULL; // Return NULL If The Filename Is Not Given } if ( File = fopen (Filename, "r ) ) // Open The File If It exists? { fclose (File); // Close The Handle return auxdibimageload (Filename); // Load The Bitmap And Return A Pointer } return NULL; // If Load Failed Return NULL 9

10 CREATE A TEXTURE OBJECT Glint texture; int LoadGLTextures() // Load Bitmaps And Convert To Textures { int Status = FALSE; // Status Indicator AUX_RGBImageRec * TextureImage; // Create Storage Space For The Textures memset ( TextureImage, 0, sizeof (void *) ); // Set The Pointer To NULL if ( TextureImage = LoadBMP( "image.bmp ) ) { Status = TRUE; // Set The Status To TRUE glgentextures(1, &texture); // Create The Texture glbindtexture(gl_texture_2d, texture); glteximage2d(gl_texture_2d, 0, 3, TextureImage -> sizex, TextureImage -> sizey, 0, GL_RGB, GL_UNSIGNED_BYTE, TextureImage -> data); gltexparameteri(gl_texture_2d,gl_texture_min_filter,gl_linear); gltexparameteri(gl_texture_2d,gl_texture_mag_filter,gl_linear); free( TextureImage ); // Free The Image Structure } // End If TextureImage == True return Status; // Return The Status } // End of Function LoadGLTextures() 10

11 Create Many Texture Objects(1) Generate a set of new texture names using void glgentextures( GLsizei n, GLuint * textures ); n: The number of texture names to be generated. textures: A pointer to the first element of an array in which the generated texture names are stored. Ex: glgentextures(3, &mytexture[0]); Enables the creation of a named texture that is bound to a texture target void glbindtexture( GLenum target, GLuint texture ); target: The target to which the texture is bound. Must have the value GL_TEXTURE_1D or GL_TEXTURE_2D. Texture: The name of a texture; the texture name cannot currently be in use. Specifies a texture image from an array of texels void glteximage2d( target, level, components, w, h, border, format, type, *texels ); 11

12 12 Create Many Texture Objects(2) :, #define num_textures 2 AUX_RGBImageRec *Image[num_textures]; // 建立指標變數以指向兩個貼圖資料之貯存空間 Gluint Texture_Name[num_textures]; memset(image, 0, sizeof (void *)*num_textures); // 使指標變數, *Image[], 先指向 NULL glgentextures(num_textures, &Texture_Name[0]); // 產生兩個貼圖名稱 // 載入二維貼圖 Image[0], 並與貼圖名稱 Texture_Name[0] 連結 if ( Image[0]= LoadBMP( image1.bmp ) )// 載入貼圖影像, 存放於 Image[0] { glbindtexture(gl_texture_2d, Texture_Name[0]); // 若欲改變預設之性質, 如 repeat 或 clamp 等, 則在此加入 gltexparameter 指令, 例如 gltexparameteri(gl_texture_2d,gl_texture_min_filter,gl_linear); glteximage2d(gl_texture_2d,0,3,image[0]->sizex, Image[0]->sizeY, 0, GL_RGB, GL_UNSIGNED_BYTE, Image[0]->data); free(image[0]);// Free the image structure } // 載入二維貼圖 Image[1], 並與貼圖名稱 Texture_Name[1] 連結 if (Image[1] = LoadBMP( image2.bmp") ) { glbindtexture(gl_texture_2d, Texture_Name[1]); glteximage2d(gl_texture_2d,0,3, Image[1]->sizeX, Image[1]->sizeY, 0, GL_RGB, GL_UNSIGNED_BYTE, Image[1]->data); free(image[1]); } *** :,, glbindtexture(gl_texture_2d, texture[1]), textrue[1] Image[1].

13 Converting A Texture Image If dimensions of image are not power of 2 gluscaleimage( format, w_in, h_in,type_in, *data_in, w_out, h_out,type_out, *data_out ); *_in is for source image *_out is for destination image Image interpolated and filtered during scaling 13

14 Specifying a Texture: Other Methods Use frame buffer as source of texture image uses current buffer as source image glcopyteximage2d(...) glcopyteximage1d(...) Modify part of a defined texture gltexsubimage2d(...) gltexsubimage1d(...) Do both with glcopytexsubimage2d(...), etc. 14

15 Mapping a Texture Based on parametric texture coordinates gltexcoord*() specified at each vertex t 0, 1 Texture Space a Object Space 1, 1 (s, t) = (0.2, 0.8) A b 0, 0 1, 0 c s (0.4, 0.2) B C (0.8, 0.4) 15

16 Tutorial: Texture Tutors\texture.exe 16

17 Controlling Filtering Specify the magnification and minification filtering methods by: gltexparameteri( target, type, mode ); Ex: gltexparameteri (GL_TEXTURE_2D, GL_TEXTURE_MAG_FILTER, GL_NEAREST); Parameter GL_TEXTURE_MAG_FILTER GL_TEXTURE_MIN_FILTER Values GL_NEAREST or GL_LINEAR GL_NEAREST, GL_LINEAR, L_NEAREST_MIPMAP_NEAREST, GL_NEAREST_MIPMAP_LINEAR, GL_LINEAR_MIPMAP_NEAREST, GL_LINEAR_MIPMAP_LINEAR 17

18 Mipmapped Textures Mipmap allows for prefiltered texture maps of decreasing resolutions Lessens interpolation errors for smaller textured objects Declare mipmap level during texture definition EX:Redbook Samples\MIPMAP.EXE glteximage*d( GL_TEXTURE_*D, level, ) glteximage2d(gl_texture_2d, 0, 3, 32, 32, 0, GL_RGB, GL_UNSIGNED_BYTE, &mipmapimage32[0][0][0]); glteximage2d(gl_texture_2d, 1, 3, 16, 16, 0, GL_RGB, GL_UNSIGNED_BYTE, &mipmapimage16[0][0][0]); Automatically generating mipmaps int glubuild1dmipmaps(glenum target, GLint components, GLint width, GLenum format, GLenum type,, void *data); Ex: glubuild2dmipmaps(gl_texture_2d, 3,, w, h, 0, GL_RGB, GL_UNSIGNED_BYTE, image_array); 18

19 Wrapping Mode void gltexparameter{if}{v}(glenum target, GLenum pname, TYPE param); Example: gltexparameteri(gl_texture_2d, GL_TEXTURE_WRAP_S, GL_CLAMP) gltexparameteri(gl_texture_2d, GL_TEXTURE_WRAP_T, GL_REPEAT) t s texture GL_REPEAT wrapping CLAMP in two direction GL_CLAMP wrapping CLAMP in two direction 19

20 Texture Functions Controls how texture is applied void gltexenv{if}{v}(glenum target, GLenum pname, TYPEparam); Ex: gltexenvi(gl_texture_2d, GL_TEXTURE_ENV_MODE, GL_MODULATE); Decal, Modulate, and Blend Functions Components Decal Mode Modulate Mode Blend Mode 1 Undefined C = LtCf, A = Af C = (1-Lt)Cf + LtCc, A = Af 2 undefined C = LtCf, A = AtAf C = (1-Lt)Cf + LtCc, A = AtAf 3 C = Ct, A = Af C = CtCf, A = Af undefined 4 C = (1-Lt)Cf + AtCt, A = Af C = CtCf, A = AtAf undefined L: Luminance value; A: Alpha value; C: an RGB color triple t indicates a texture value, f indicates a fragment value,c indicates the values assigned with GL_TEXTURE_ENV_COLOR 20

21 Perspective Correction Hint Texture coordinate and color interpolation either linearly in screen space or using depth/perspective values (slower) Noticeable for polygons on edge glhint( GL_PERSPECTIVE_CORRECTION_HINT, hint ) where hint is one of GL_DONT_CARE GL_NICEST GL_FASTEST 21

22 Is There Room for a Texture? Query largest dimension of texture image typically largest square texture doesn t consider internal format size glgetintegerv( GL_MAX_TEXTURE_SIZE, &size ) Texture proxy will memory accommodate requested texture size? no image specified; placeholder if texture won t fit, texture state variables set to 0 doesn t know about other textures only considers whether this one texture will fit all of memory 22

23 Automatically Generating Texture Coordinates OpenGL can automatically generate texture coordinates Control the generation of texture coordinates by calling gltexgen{ifd}[v](glenum coord, GLenum pname, GLint param ) Redbook Samples\TEXGEN.EXE coord : A texture coordinate. Must be one of the following: GL_S, GL_T, GL_R, or GL_Q. (one of the (s,t,r,q) texture coordinates) pname : The symbolic name of the texture-coordinate generation function. Must be GL_TEXTURE_GEN_MODE. param : A single-valued texture generation parameter, one of GL_OBJECT_LINEAR, GL_EYE_LINEAR, GL_SPHERE_MAP 23