1. Texture Mapping
고려대학교 컴퓨터 그래픽스 연구실
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2. Contents Texels and textures Constructing a texture map
Texture coordinates
Texture parameters
A rotating cube with texture
Texture mapping with images
Exercise
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3. Texels and Textures Texels – texture elements
Texture coordinates (s, t)
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4. Constructing a Texture Map
Steps:
Read an image for the texture map
Define parameters that determine how the texture should be applied
Define texture coordinates for the vertices
Ex: making the image into a 2D texture map
GLubyte myimage[64][64][3];
glEnable(GL_TEXTURE_2D);
glTexImage2D(GL_TEXTURE_2D, 0, 3, 64, 64, 0,
GL_RGB, GL_UNSIGNED_BYTE, myimage);
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5. 1D, 2D, & 3D Texture Maps
void glTexImage1D(GLenum target, GLint level,
GLint iformat, GLsizei width,
GLint border, GLenum format,
GLenum type, Glvoid *texels);
void glTexImage2D(GLenum target, GLint level,
GLint iformat, GLsizei width,
GLsizei height, GLint border,
GLenum format, GLenum type,
Glvoid *texels);
void glTexImage3D(GLenum target, GLint level,
GLint iformat, GLsizei width,
GLsizei height, Glsizei depth,
GLint border, GLenum format,
GLenum type, Glvoid *texels);
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6. 2D Texture Map
Texture map as a continuous image in (s, t) space and as a discrete image
Texture Map
Texture Image
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7. Texture Coordinates (1/2)
Mapping between points on geometric objects and texels
Ex: mapping the texture to a quadrilateral
void glTexCoord{1234}{sifd}(TYPE scoord, ...);
void glTexCoord{1234}{sifd}v(TYPE *coord);
glBegin(GL_QUADS);
glTexCoord2f(0.0, 0.0); glVertex3fv(vertex[0]);
glTexCoord2f(0.0, 1.0); glVertex3fv(vertex[1]);
glTexCoord2f(1.0, 1.0); glVertex3fv(vertex[2]);
glTexCoord2f(1.0, 0.0); glVertex3fv(vertex[3]);
glEnd();
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8. Texture Coordinates (2/2)
Applying a checkerboard texture to a quadrilateral
Texture Map
Quadrilateral
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9. Texture Parameters (1/3)
Control over how the texture is applied to the surface
Ex: deciding what to do if values are out of (0, 1)
GL_CLAMP
void glTexParameter{if}(GLenum target, GLenum name,
TYPE value);
void glTexParameter{if}v(GLenum target, GLenum name,
TYPE *value);
glTexParameter(GL_TEXTURE_2D, GL_TEXTURE_WRAP_S,
GL_REPEAT);
glTexParameter(GL_TEXTURE_2D, GL_TEXTURE_WRAP_T,
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10. Texture Parameters (2/3)
Preimage of the pixel
Texture mapping is not really applied to the surface but rather a pixel in screen coordinates
Magnification – each texel covers multiple pixels
Minification – each pixel covers multiple texels
Magnification
Minification
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11. Texture Parameters (3/3)
Point sampling
OpenGL uses to average a 2X2 array of neighboring texels
GL_LINEAR
glTexParameter(GL_TEXTURE_2D, GL_TEXTURE_MAG_FILTER,
GL_NEAREST);
glTexParameter(GL_TEXTURE_2D, GL_TEXTURE_MIN_FILTER,
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12. A Rotating Cube with Texture
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13. Constructor
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14. DrawQuad( )
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15. DrawScene( )
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16. A Color Cube
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17. Texture Image
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18. LoadTexture( )
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19. DrawQuad( )
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20. DrawScene( )
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21. A Color Cube with Texture
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22. Exercise (1)
Change the texture coordinates, parameters for texture mapping
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23. Texture Images
Load a BMP file for a texture image
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24. OpenGL Auxiliary Library
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25. Project Settings
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26. New Definition
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27. LoadTexture( )
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28. Result – Texture Mapping (1)
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29. Multiple Texture Images
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30. LoadTexture( )
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31. DrawScene( )
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32. Result – Texture Mapping (2)
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33. Exercise (2)
Set the background by texture mapping
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