Open GL Super Bible:Texture Mapping















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Open GL Super Bible


(Publisher: Macmillan Computer Publishing)

Author(s): Waite group Press

ISBN: 1571690735

Publication Date: 08/01/96

 




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Reference Section
glTexCoord

Purpose
Specifies the current texture image coordinate for textured polygon rendering.
Include File
<GL/gl.h>
Syntax
void glTexCoord1{dfis}(TYPE s);

void glTexCoord1{dfis}v(TYPE *s);

void glTexCoord2{dfis}(TYPE s, TYPE t);

void glTexCoord2{dfis}v(TYPE *st);

void glTexCoord3{dfis}(TYPE s, TYPE t, TYPE r);

void glTexCoord3{dfis}v(TYPE *stq);

void glTexCoord4{dfis}(TYPE s, TYPE t, TYPE r, TYPE q);

void glTexCoord4{dfis}v(TYPE *strq);
Description
These functions set the current texture image
coordinate in 1
4 dimensions. For example, the s and t parameters
correspond to the horizontal and vertical image coordinates of a 2D
texture image.


Parameters

s

The horizontal texture image coordinate.
t

The vertical texture image coordinate.
r

The texture image depth coordinate.
q

The texture image “time" coordinate.
Returns
None.
Example
See the example in CH12\TEXSCENE.C on the source code CD-ROM.
See Also
glTexEnv, glTexGen, glTexImage1D, glTexImage2D,
glTexParameter


glTexEnv

Purpose
Sets texturing parameters.
Include File
<GL/gl.h>
Syntax
void glTexEnvf(GLenum target, GLenum pname, GLfloat param);

void glTexEnvfv(GLenum target, GLenum pname, GLfloat *param);

void glTexEnvi(GLenum target, GLenum pname, GLint param);

void glTexEnviv(GLenum target, GLenum pname, GLint *param);
Description
The glTexEnv functions set texture-mapping
parameters that control how texture images are mapped to polygons. The
GL_DECAL texturing mode uses a texture image directly to draw polygon.
GL_BLEND and GL_MODULATE texture modes use the GL_TEXTURE_ENV_COLOR
color and the current framebuffer to determine what pixels are textured.


Parameters

target

GLenum: The texture environment to define; must be GL_TEXTURE_ENV.

pname

GLenum: The parameter name to define. Valid names are as follows:

GL_TEXTURE_ENV_MODE Specifies the type of texturing to do.

GL_TEXTURE_ENV_COLOR Specifies the color to use for blending.
param

The parameter value. For GL_TEXTURE_ENV_COLOR,
param is a pointer to an RGBA color value. For GL_TEXTURE_ENV_MODE, it
can be one of the following constants:





GL_DECAL
Texture images are directly mapped to the framebuffer.

GL_BLEND
Texture images are blended with a constant color (GL_TEXTURE_ENV_ COLOR) before being mapped to the framebuffer.

GL_MODULATE
Texture images are multiplied with the
framebuffer before being mapped to it.



Returns
None.
Example
See the example in CH12\TEXSCENE.C on the source code CD-ROM.
See Also
glTexCoord, glTexGen, glTexImage1D,
glTexImage2D, glTexParameter


glTexGen

Purpose
Defines parameters for texture coordinate generation.
Include File
<GL/gl.h>
Syntax
void glTexGend(GLenum coord, GLenum pname, GLdouble param);

void glTexGenf(GLenum coord, GLenum pname, GLfloat param);

void glTexGeni(GLenum coord, GLenum pname, GLint param);

void glTexGendv(GLenum coord, GLenum pname, GLdouble *param);

void glTexGenfv(GLenum coord, GLenum pname, GLfloat *param);

void glTexGeniv(GLenum coord, GLenum pname, GLint *param);
Description
This function sets parameters for texture coordinate generation when one or more of GL_TEXTURE_GEN_S, GL_TEXTURE_GEN_T, GL_TEXTURE_GEN_R, or GL_TEXTURE_GEN_Q is enabled with glEnable.
When GL_TEXTURE_GEN_MODE is set to
GL_OBJECT_LINEAR, texture coordinates are generated by multiplying the
current object (vertex) coordinates by the constant vector specified by
GL_OBJECT_PLANE:


coordinate = v[0] * p[0] + v[1] * p[1] + v[2] * p[2] + v[3] * p[3]


For GL_EYE_LINEAR, the eye coordinates (object coordinate multiplied through the GL_MODELVIEWmatrix) are used.
When GL_TEXTURE_GEN_MODE is set to
GL_SPHERE_MAP, coordinates are generated in a sphere about the current
viewing position or origin.


Parameters

coord

GLenum: The texture coordinate to map. Must be one of GL_S, GL_T, GL_R, or GL_Q.
pname

GLenum: The parameter to set. Must be one of GL_TEXTURE_GEN_MODE, GL_OBJECT_PLANE, or GL_EYE_PLANE.
param

The parameter value. For GL_TEXTURE_GEN_MODE,
param is one of the following:





GL_OBJECT_LINEAR
Texture coordinates are calculated from object (vertex) coordinates.

GL_EYE_LINEAR
Texture coordinates are calculated by eye coordinates (object coordinates multiplied through the GL_MODELVIEW matrix).

GL_SPHERE_MAP
Texture coordinates are generated in a
sphere around the viewing position.



For GL_OBJECT_PLANE and GL_EYE_PLANE, param is a 4-element array that is used as a multiplier for object or eye coordinates.
Returns
None.
Example
See the example in CH12\TEXSCEN2.C on the source code CD-ROM.
See Also
glTexCoord, glTexEnv, glTexImage1D,
glTexImage2D, glTexParameter






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