Grafica Computazionale

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1 Grafica Computazionale lezione36 Informatica e Automazione, "Roma Tre" June 3, 2010

2 Grafica Computazionale: Lezione 33 Textures Introduction Steps in Texture Mapping A Sample Program Texturing algorithms

3 Contents Textures Introduction Steps in Texture Mapping A Sample Program Texturing algorithms

4 OpenGL examples source Main reference:

5 OpenGL examples source Main reference:

6 OpenGL examples source Main reference:

7 OpenGL examples source Main reference: Chapter 5 of Geometric Programming for Computer Aided Design

8 Teaching Texture Mapping Visually

9 It is cheaper to employ mapping techniques than to use myriads of tiny polygons

10 Steps in Texture Mapping

11 Steps in Texture Mapping 1. Create a texture object and specify a texture for that object.

12 Steps in Texture Mapping 1. Create a texture object and specify a texture for that object. 2. Indicate how the texture is to be applied to each pixel.

13 Steps in Texture Mapping 1. Create a texture object and specify a texture for that object. 2. Indicate how the texture is to be applied to each pixel. 3. Enable texture mapping.

14 Steps in Texture Mapping 1. Create a texture object and specify a texture for that object. 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.

15 checker.py In this program from red book, which is very simple, a single texture object is created to maintain a single uncompressed, two-dimensional texture

16 checker.py In this program from red book, which is very simple, a single texture object is created to maintain a single uncompressed, two-dimensional texture This example does not find out how much memory is available

17 checker.py In this program from red book, which is very simple, a single texture object is created to maintain a single uncompressed, two-dimensional texture This example does not find out how much memory is available Since only one texture is created, there is no attempt to prioritize or otherwise manage a working set of texture objects

18 checker.py In this program from red book, which is very simple, a single texture object is created to maintain a single uncompressed, two-dimensional texture This example does not find out how much memory is available Since only one texture is created, there is no attempt to prioritize or otherwise manage a working set of texture objects Other advanced techniques, such as texture borders, mipmaps, or cube maps, are not used in this simple example.

19 Create a Texture Object and Specify a Texture for That Object A texture is usually thought of as being two-dimensional, like most images

20 Create a Texture Object and Specify a Texture for That Object A texture is usually thought of as being two-dimensional, like most images but it can also be one-dimensional or three-dimensional

21 Create a Texture Object and Specify a Texture for That Object A texture is usually thought of as being two-dimensional, like most images but it can also be one-dimensional or three-dimensional The data describing a texture may consist of one, two, three, or four elements per texel

22 Create a Texture Object and Specify a Texture for That Object A texture is usually thought of as being two-dimensional, like most images but it can also be one-dimensional or three-dimensional The data describing a texture may consist of one, two, three, or four elements per texel and may represent an (R, G, B, A) quadruple, a modulation constant, or a depth component.

23 Create a Texture Object and Specify a Texture for That Object The checkerboard texture is generated in the routine makecheckimage(), and all the texture-mapping initialization occurs in the routine init()

24 Create a Texture Object and Specify a Texture for That Object The checkerboard texture is generated in the routine makecheckimage(), and all the texture-mapping initialization occurs in the routine init() glgentextures() and glbindtexture() name and create a texture object for a texture image

25 Create a Texture Object and Specify a Texture for That Object The checkerboard texture is generated in the routine makecheckimage(), and all the texture-mapping initialization occurs in the routine init() glgentextures() and glbindtexture() name and create a texture object for a texture image The single, full-resolution texture map is specified by glteximage2d(), whose parameters indicate the size, type, location, and other properties of the texture image

26 Create a Texture Object and Specify a Texture for That Object The checkerboard texture is generated in the routine makecheckimage(), and all the texture-mapping initialization occurs in the routine init() glgentextures() and glbindtexture() name and create a texture object for a texture image The single, full-resolution texture map is specified by glteximage2d(), whose parameters indicate the size, type, location, and other properties of the texture image (See Specifying the Texture for more information about glteximage2d().)

27 Indicate How the Texture Is to Be Applied to Each Pixel You can choose any of four possible functions for computing the final RGBA value from the fragment color and the texture image data

28 Indicate How the Texture Is to Be Applied to Each Pixel You can choose any of four possible functions for computing the final RGBA value from the fragment color and the texture image data One possibility is simply to use the texture color as the final color; this is the replace mode, in which the texture is painted on top of the fragment, just as a decal would be applied

29 Indicate How the Texture Is to Be Applied to Each Pixel You can choose any of four possible functions for computing the final RGBA value from the fragment color and the texture image data One possibility is simply to use the texture color as the final color; this is the replace mode, in which the texture is painted on top of the fragment, just as a decal would be applied (checker.py uses replace mode.) Another method is to use the texture to modulate, or scale, the fragment s color; this technique is useful for combining the effects of lighting with texturing

30 Indicate How the Texture Is to Be Applied to Each Pixel You can choose any of four possible functions for computing the final RGBA value from the fragment color and the texture image data One possibility is simply to use the texture color as the final color; this is the replace mode, in which the texture is painted on top of the fragment, just as a decal would be applied (checker.py uses replace mode.) Another method is to use the texture to modulate, or scale, the fragment s color; this technique is useful for combining the effects of lighting with texturing Finally, a constant color can be blended with that of the fragment, based on the texture value.

31 Indicate How the Texture Is to Be Applied to Each Pixel You can choose any of four possible functions for computing the final RGBA value from the fragment color and the texture image data (gltexenv)

32 Indicate How the Texture Is to Be Applied to Each Pixel You can choose any of four possible functions for computing the final RGBA value from the fragment color and the texture image data (gltexenv) use the texture color as the final color; this is the replace mode, in which the texture is painted on top of the fragment, just as a decal would be applied.

33 Indicate How the Texture Is to Be Applied to Each Pixel You can choose any of four possible functions for computing the final RGBA value from the fragment color and the texture image data (gltexenv) use the texture color as the final color; this is the replace mode, in which the texture is painted on top of the fragment, just as a decal would be applied. use the texture to modulate, or scale, the fragment s color; this technique is useful for combining the effects of lighting with texturing.

34 Indicate How the Texture Is to Be Applied to Each Pixel You can choose any of four possible functions for computing the final RGBA value from the fragment color and the texture image data (gltexenv) use the texture color as the final color; this is the replace mode, in which the texture is painted on top of the fragment, just as a decal would be applied. use the texture to modulate, or scale, the fragment s color; this technique is useful for combining the effects of lighting with texturing. a constant color can be *blend*ed with that of the fragment, based on the texture value.

35 checker.py The four calls to gltexparameter() specify how the texture is to be wrapped

36 checker.py The four calls to gltexparameter() specify how the texture is to be wrapped and how the colors are to be filtered if there isn t an exact match between texels in the texture and pixels on the screen

37 checker.py The four calls to gltexparameter() specify how the texture is to be wrapped and how the colors are to be filtered if there isn t an exact match between texels in the texture and pixels on the screen (See Filtering on page 434 and Repeating and Clamping Textures on page 452 of red book)

38 Enable Texture Mapping You need to enable texturing before drawing your scene

39 Enable Texture Mapping You need to enable texturing before drawing your scene Texturing is enabled or disabled using glenable() or gldisable(), with the symbolic constant GL_TEXTURE_1D, GL_TEXTURE_2D, GL_TEXTURE_3D, or GL_TEXTURE_CUBE_MAP for one-, two-, three-dimensional, or cube map texturing, respectively

40 Enable Texture Mapping You need to enable texturing before drawing your scene Texturing is enabled or disabled using glenable() or gldisable(), with the symbolic constant GL_TEXTURE_1D, GL_TEXTURE_2D, GL_TEXTURE_3D, or GL_TEXTURE_CUBE_MAP for one-, two-, three-dimensional, or cube map texturing, respectively If two or all three of the dimensional texturing modes are enabled, the largest dimension enabled is used

41 Enable Texture Mapping You need to enable texturing before drawing your scene Texturing is enabled or disabled using glenable() or gldisable(), with the symbolic constant GL_TEXTURE_1D, GL_TEXTURE_2D, GL_TEXTURE_3D, or GL_TEXTURE_CUBE_MAP for one-, two-, three-dimensional, or cube map texturing, respectively If two or all three of the dimensional texturing modes are enabled, the largest dimension enabled is used If cube map textures are enabled, it trumps all the others

42 Enable Texture Mapping You need to enable texturing before drawing your scene Texturing is enabled or disabled using glenable() or gldisable(), with the symbolic constant GL_TEXTURE_1D, GL_TEXTURE_2D, GL_TEXTURE_3D, or GL_TEXTURE_CUBE_MAP for one-, two-, three-dimensional, or cube map texturing, respectively If two or all three of the dimensional texturing modes are enabled, the largest dimension enabled is used If cube map textures are enabled, it trumps all the others For the sake of clean programs, you should enable only the one you want to use.

43 checker.py In display(),

44 checker.py In display(), glenable() turns on texturing

45 checker.py In display(), glenable() turns on texturing gltexenv() sets the drawing mode to GL_REPLACE so that the textured polygons are drawn using the colors from the texture map

46 checker.py In display(), glenable() turns on texturing gltexenv() sets the drawing mode to GL_REPLACE so that the textured polygons are drawn using the colors from the texture map rather than taking into account the color in which the polygons would have been drawn without the texture

47 Draw the Scene, Supplying Both Texture and Geometric Coordinates For a 2D texture map the texture coordinates range from 0.0 to 1.0 in both directions, but the coordinates of the items being textured can be anything

48 Draw the Scene, Supplying Both Texture and Geometric Coordinates For a 2D texture map the texture coordinates range from 0.0 to 1.0 in both directions, but the coordinates of the items being textured can be anything To apply the brick texture to a wall, for example, the code would probably assign texture coordinates (0, 0), (1, 0), (1, 1), and (0, 1) to the four corners of the wall

49 Draw the Scene, Supplying Both Texture and Geometric Coordinates For a 2D texture map the texture coordinates range from 0.0 to 1.0 in both directions, but the coordinates of the items being textured can be anything To apply the brick texture to a wall, for example, the code would probably assign texture coordinates (0, 0), (1, 0), (1, 1), and (0, 1) to the four corners of the wall If the wall is large, you might want to paint several copies of the texture map on it

50 Draw the Scene, Supplying Both Texture and Geometric Coordinates For a 2D texture map the texture coordinates range from 0.0 to 1.0 in both directions, but the coordinates of the items being textured can be anything To apply the brick texture to a wall, for example, the code would probably assign texture coordinates (0, 0), (1, 0), (1, 1), and (0, 1) to the four corners of the wall If the wall is large, you might want to paint several copies of the texture map on it If you do so, the texture map must be designed so that the bricks at the left edge match up nicely with the bricks at the right edge, and similarly for the bricks at the top and bottom.

51 checker.py Then, two polygons are drawn

52 checker.py Then, two polygons are drawn Note that texture coordinates are specified along with vertex coordinates

53 checker.py Then, two polygons are drawn Note that texture coordinates are specified along with vertex coordinates The gltexcoord() command behaves similarly to the glnormal() command

54 checker.py Then, two polygons are drawn Note that texture coordinates are specified along with vertex coordinates The gltexcoord() command behaves similarly to the glnormal() command gltexcoord() sets the current texture coordinates; any subsequent vertex command has those texture coordinates associated with it until gltexcoord() is called again.

55 Contents Textures Introduction Steps in Texture Mapping A Sample Program Texturing algorithms

56 """1* checker.c * This program texture maps a checker board image onto * two rectangles. * * * If running this program on DpenGL 1.0, texture objects are not used. *1""" from OpenGL.GL import * from OpenGL.GLU import * from OpenGL.GLUT import * import nwnpy from array import * #1* Create checkerboard texture *1 checkimagewidth : 64 checkimageheight : 64 checkimage : nwnpy.array(bytearray(checkimagewidth*checkimageheight*4» texname : 1, #Remark: is a TUPLE def makecheckimage(checkimageheight,checkimagewidth): global checkimage def ind(i,j,k): return (i*checkimagewidth +j)*4 + k for i in range(checkimageheight): for j in range(checkimagewidth) : # [i & Ox8 for i in range(64)] a,b : (i & Ox8 :: 0)*1, (j & Ox8 :: 0)*1 if (a and not b) or (b and not a): c : 255 else: c : 0 # c ((((i&oxb) O)'((j&OxB»" O»*255; checkimage(ind(i,j,o)] - c checkimage(ind(i,j,l)] - c checkimage(ind(i,j,2)] - c checkimage(ind(i,j,3)] - 255

57 - - def init(): glclearcolor (1.0, 0.0, 0.0, 0.0) glshademodel(gl FLAT) glenable(gl_depth_test) makecheckimage (checkimageheight, checkimagewidth) print checkimage[o:-l] glpixelstorei(gl UNPACK ALIGNMENT, 1) - - glgentextures(l, texname); glbindtexture(gl TEXTURE 2D, texname[o]); gltexparameteri(gl_texture_2d, GL_TEXTURE_WRAP_S, GL_CLAMP) gltexparameteri(gl_texture_2d, GL_TEXTURE_WRAP_T, GL_CLAMP) gltexparameteri(gl_texture_2d, GL_TEXTURE_MAG_FILTER, GL_NEAREST) gltexparameteri(gl_texture_2d, GL_TEXTURE_MIN_FILTER, GL_NEAREST) glteximage2d(gl_texture_2d, 0, GL_RGBA, checkimagewidth, checkimageheight, 0, GL_RGBA, GL_UNSIGNED_BYTE, checkimage) print "OK"

58 I def display(): glclear(gl_color_buffer_bit I GL_DEPTH_BUFFER_BIT) glenable(gl_texture_2d) gltexenv (GL_TEXTURE_ENV, GL_TEXTURE_ENV_MODE, GL DECAL) glbindtexture(gl_texture_2d, texname[o]); print glistexture(texname[o])==gl_true glbegin(gl QUADS) gltexcoord2f(o.o, 0.0); glvertex3f(-2.0, -1.0, 0.0) gltexcoord2f(o.o, 1.0); glvertex3f(-2.0, 1.0, 0.0) gltexcoord2f(1.o, 1.0); glvertex3f(o.o, 1.0, 0.0) gltexcoord2f(1.o, 0.0); glvertex3f(o.o, -1.0, 0.0) gltexcoord2f(o.o, 0.0); glvertex3f(1.o, -1.0, 0.0) gltexcoord2f(o.o, 1.0); glvertex3f(1.o, 1.0, 0.0) gltexcoord2f(1.o, 1.0); glvertex3f( , 1.0, ) gltexcoord2f(1.o, 0.0); glvertex3f( , -1.0, ) glend( ) glflush( ) gldisable(gl_texture_2d)

def reshape{w, h): glviewport{o, 0, w, h) glmatrixmode{gl PROJECTION) glloadidentity{) gluperspective{60.0, float{w)/float{h), 1.0, 30.0) glmatrixmode{gl MODELVIEW) glloadidentity{) gltranslatef{o.

59 def reshape{w, h): glviewport{o, 0, w, h) glmatrixmode{gl PROJECTION) glloadidentity{) gluperspective{60.0, float{w)/float{h), 1.0, 30.0) glmatrixmode{gl MODELVIEW) glloadidentity{) gltranslatef{o.o, 0.0, -3.6) I def keyboard{key, x, y): if key == chr(27): sys.exit{o) # Main program entry point if name " main ": glutinit{ ) glutinitdisplaymode{glut_single I GLUT RGB I GLUT_DEPTH) glutinitwindowsize{250, 250) glutinitwindowposition{loo, 100) glutcreatewindow{"checker") ini t () glutdisplayfunc{display) glutreshapefunc{reshape) glutkeyboardfunc{keyboard) glutmainloop{ )

60 Textured checkboard

61 Different texture checkimagewidth, checkimageheight = 16, 16

62 Texturing out of space (S, T ) = [0, 1] 2, clamped gltexparameteri(gl_texture_2d, GL_TEXTURE_WRAP_S, GL_CLAMP) gltexparameteri(gl_texture_2d, GL_TEXTURE_WRAP_T, GL )

63 Texturing out of space (S, T ) = [0, 1] 2, repeated gltexparameteri(gl_texture_2d, GL_TEXTURE_WRAP_S, GL_REPEAT) gltexparameteri(gl_texture_2d, GL_TEXTURE_WRAP_T, GL_REPEAT)

64 Contents Textures Introduction Steps in Texture Mapping A Sample Program Texturing algorithms

65 Bounding volume Depending on the mapping situation, we may need to bound an object with a box, a cylinder, or a sphere.

66 Planar texture mapping For a planar map, we take an (x,y,z) value from the object and project one of the components. We use the planar coordinate to look up the color in the texture map.

67 Planar texture mapping? (checker1.py)

Chapter 9 Texture Mapping An Overview and an Example Steps in Texture Mapping A Sample Program Specifying the Texture Texture Proxy Replacing All or

Chapter 9 Texture Mapping An Overview and an Example Steps in Texture Mapping A Sample Program Specifying the Texture Texture Proxy Replacing All or Part of a Texture Image One Dimensional Textures Using