COMP471 Computer Graphics

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COMP471 Computer Graphics

• OpenGL Texture Mapping

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The Need

• Create complex appearance w/o much computational
  effort

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Texture Def

• A detailed pattern repeated many times to tile a
  given plane
• A multidimensional image mapped to a multidim.
  space.

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Texture Mapping

• A technique to improve the appearance of the
  objects shaded with a light model
• Function of mapping an image onto a 3D surface
• Provide color details for complex surfaces

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Viewing

• 2D Texture Space
• 3D Model Space
• 2D Screen Space

parameterization
compound mapping
projection
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Texture in OpenGL

• Identified by an integer name
• The procedure
• Need to generate names first (glGenTextures())
• Load images (see texture.h for BMPLoader for
  example)
• Bind loaded binary image data to the integer name
  (glBindTexture)
• Set parameters (glTexParameter())
• Build mipmaps (e.g. gluBuild2DMipmaps())
• When drawing an object
• Enable texturing
• Specify a texture by its name
• Disable texture mode

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Reading Textures

• readAllTextures()

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Mapping Texture on Flat Surfaces and Quadric
Objects

• Cube
• Sphere
• Spheremap

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Cube
glEnable(GL_TEXTURE_2D) glBindTexture(GL_TEXTURE_
2D, m_aiTexNamesp_iFaceColor) draw cubes
face glDisable(GL_TEXTURE_2D)
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Sphere
glEnable(GL_TEXTURE_2D) glBindTexture(GL_TEXTURE_
2D, m_iTexName) GLUquadricObj l_poQuadric
gluNewQuadric() gluQuadricDrawStyle(l_poQuadric,
GLU_FILL) gluQuadricNormals(l_poQuadric,
GLU_SMOOTH) gluQuadricTexture(l_poQuadric,
GL_TRUE) gluSphere(l_poQuadric, 0.5, 30,
30) gluDeleteQuadric(l_poQuadric) glDisable(GL_
TEXTURE_2D)
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Spheremap

• Spheremap texture looks like reflection of a
  sphere projected to a plane

180
eye
90
0
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Spheremap

• Spheremap texture is indexed from a reflection
  vector
• All computations are relative to the eye position
• Texture looks like a reflection from a chrome
  hemisphere
• All mapping is done as reflection from
  hemisphere.
• Maps center reflects back to eyes

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Generating Spheremap OpenGL
glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MIN_FILT
ER, GL_NEAREST) glTexParameteri(GL_TEXTURE_2D,
GL_TEXTURE_MAG_FILTER, GL_NEAREST) glTexGeni(GL_S
, GL_TEXTURE_GEN_MODE, GL_SPHERE_MAP) glTexGeni(G
L_T, GL_TEXTURE_GEN_MODE, GL_SPHERE_MAP) glEnable
(GL_TEXTURE_GEN_S) glEnable(GL_TEXTURE_GEN_T) gl
TexEnvi(GL_TEXTURE_ENV, GL_TEXTURE_ENV_MODE,
GL_DECAL) glTexParameteri(GL_TEXTURE_2D,
GL_TEXTURE_WRAP_S, GL_REPEAT) glTexParameteri(GL_
TEXTURE_2D, GL_TEXTURE_WRAP_T, GL_REPEAT) comput
eNormalsForYourObject() drawYourObject()
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References

• Jianxiang Dong Slides from Fall 2001