OpenGL Texture Mapping

1
OpenGL Texture Mapping

• Holmes Chiou
• 2002

2
Introduction

• Texture mapping allows you to glue an image of a
  brick wall to a polygon and to draw the entire
  wall as a single polygon

3
Introduction

• Create a texture object and specify a texture for
  that object
• Indicate how the texture is to be applied to each
  pixel
• Enable texture mapping
• Draw the scene, supplying both texture and
  geometric coordinates

4
Introduction

• static GLuint texName1
• glPixelStorei(GL_UNPACK_ALIGNMENT, 1)
• glGenTextures(1, texName)
• glBindTexture(GL_TEXTURE_2D, texName0)
• 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_FILT
  ER, GL_NEAREST)
• glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MIN_FILT
  ER, GL_NEAREST)
• glTexImage2D(GL_TEXTURE_2D, 0, GL_RGBA, 32, 32,
  0, GL_RGBA, GL_UNSIGNED_BYTE, texImage32 )
• glEnable(GL_TEXTURE_2D)

5
Texture Object -1

• New concept in OpenGL 1.1
• Operate texture as an object
• Steps to use texture object
• Generate texture names
• Bind texture objects to texture data parameters
• Rebind the texture objects for applying

6
Texture Object -2

• Naming a texture object
• void glGenTextures(GLsizei n, GLuint
  textureNames)
• glIsTexture() determines if a texture name is
  actually in use

7
Texture Object -3

• Bind a texture name to a texture object
• void glBindTexture(GLenum target, GLuint
  textureName)
• Cleaning up texture objects
• void glDeleteTextures(GLsizei n, const GLuint
  textureNames)

8
Specifying Texture

• void glTexImage2D(GLenum target, GLint level,
  GLint internalFormat, GLsizei width, GLsizei
  height, GLint border, GLenum format, GLenum
  type, const GLvoid pixels)
• Ref. OpenGL Programming Guide for parameters
  detail
• glPixelStorei(GL_UNPACK_ALIGNMENT, 1)
• Ex
• glTexImage2D(GL_TEXTURE_2D, 0, GL_RGBA, 32, 32,
  0, GL_RGBA, GL_UNSIGNED_BYTE, texImage32)

9
Mip-Mapping -1

• Multi-resolution texture
• Specified in the level parameter in
  glTexImage2D

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Mip-Mapping -2

• For example
• glTexImage2D(GL_TEXTURE_2D, 0, GL_RGBA, 32, 32,
  0, GL_RGBA, GL_UNSIGNED_BYTE, mipmapImage32)
• glTexImage2D(GL_TEXTURE_2D, 1, GL_RGBA, 16, 16,
  0, GL_RGBA, GL_UNSIGNED_BYTE, mipmapImage16)
• glTexImage2D(GL_TEXTURE_2D, 2, GL_RGBA, 8, 8, 0,
  GL_RGBA, GL_UNSIGNED_BYTE, mipmapImage8)
• glTexImage2D(GL_TEXTURE_2D, 3, GL_RGBA, 4, 4, 0,
  GL_RGBA, GL_UNSIGNED_BYTE, mipmapImage4)
• glTexImage2D(GL_TEXTURE_2D, 4, GL_RGBA, 2, 2, 0,
  GL_RGBA, GL_UNSIGNED_BYTE, mipmapImage2)
• glTexImage2D(GL_TEXTURE_2D, 5, GL_RGBA, 1, 1, 0,
  GL_RGBA, GL_UNSIGNED_BYTE, mipmapImage1)

11
Mip-Mapping -3

• Using GLU helper
• int gluBuild2DMipmaps(GLenum target, GLint
  components, GLint width,GLint height, GLenum
  format, GLenum type, void data)
• gluBuild2DMipmaps( GL_TEXTURE_2D, 3, 32, 32,
  GL_RGB, GL_UNSIGNED_BYTE, texImage32 )

12
Filtering -1

• Magnification Minification
• Using glTexParameter()
• glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MAG_FILT
  ER, GL_NEAREST)
• glTexParameteri(GL_TEXTURE_2D,
  GL_TEXTURE_MIN_FILTER, GL_NEAREST)

13
Filtering -2
14
Texture Function -1

• void glTexEnvifv(GLenum target, GLenum pname,
  TYPE param)
• target must be GL_TEXTURE_ENV
• If pname is GL_TEXTURE_ENV_MODE, param can be
  GL_DECAL, GL_REPLACE, GL_MODULATE, GL_BLEND
• If pname is GL_TEXTURE_ENV_COLOR, param is a
  color array. These values are used only if the
  GL_BLEND texture function has been specified

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Texture Function -2
16
Texture Function -3
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Assigning Texture Coordinates

• void glTexCoord1234sifd(TYPEcoords)void
  glTexCoord1234sifdv(TYPE coords)
• glTexCoord2f( 0.5, 0.5 )
• Texture Matrix Stack
• glMatrixMode( GL_TEXTURE )
• Not mentioned here

18
Repeating and Clamping Texture -1

• Using glTexParameter()
• glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_WRAP_S,
  GL_REPEAT)
• glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_WRAP_T,
  GL_CLAMP)
• Repeating a texture

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Repeating and Clamping Texture -2

• Clamping a texture
• Repeating and Clamping a texture

20
Texture Parameters
21
Automatic Texture-Coordinate Generation -1

• void glTexGenifd(GLenum coord, GLenum pname,
  TYPEparam)void glTexGenifdv(GLenum coord,
  GLenum pname, TYPE param)
• coord can be GL_S, GL_T, GL_R, GL_Q
• If pname is GL_TEXTURE_GEN_MODE, param is either
  GL_OBJECT_LINEAR, GL_EYE_LINEAR, GL_SPHERE_MAP
• If pname is GL_OBJECT_PLANE or GL_EYE_PLANE,
  param is the plane coefficients array
• Ex
• plane equation is 1x 2y 3z 0
• GLfloat plane4 1, 2, 3, 0

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Automatic Texture-Coordinate Generation -2

• (a) The texture contour stripes are parallel to
  the plane x 0, (GL_OBJECT_LINEAR).
• As the object moves, the texture appears to be
  attached to it.
• (b) A different planar equation (x y z 0)
  is used, so the stripes have a different
  orientation.
• (c) The texture coordinates are calculated
  relative to eye coordinates and hence aren't
  fixed to the object (GL_EYE_LINEAR).
• As the object moves, it appears to "swim" through
  the texture

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Automatic Texture-Coordinate Generation -3

• Environment Mapping
• To automatically generate the texture coordinates
  to support environment mapping, use this code in
  your program
• glTexGeni(GL_S, GL_TEXTURE_GEN_MODE,
  GL_SPHERE_MAP)
• glTexGeni(GL_T, GL_TEXTURE_GEN_MODE,
  GL_SPHERE_MAP)
• glEnable(GL_TEXTURE_GEN_S)
• glEnable(GL_TEXTURE_GEN_T)
• The GL_SPHERE_MAP constant creates the proper
  texture coordinates for the environment mapping.

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Automatic Texture-Coordinate Generation -4

• Sphere map
• Ref. OpenGL Programming Guide, Chapter 9 for more
  detail

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Any Question?

• ?