Linux Manual Pages

Free Software * Books

Source Code

Free Media

Linux

GLTEXGEN

HOME

GLTEXGEN

NAME
C SPECIFICATION
PARAMETERS
C SPECIFICATION
PARAMETERS
DESCRIPTION
ERRORS
ASSOCIATED GETS
SEE ALSO

NAME

glTexGend, glTexGenf, glTexGeni, glTexGendv, glTexGenfv, glTexGeniv − control the generation of texture coordinates

C SPECIFICATION

void glTexGend( GLenum coord,

	GLenum pname,
	GLdouble param )

void glTexGenf( GLenum coord,

	GLenum pname,
	GLfloat param )

void glTexGeni( GLenum coord,

	GLenum pname,
	GLint param )

PARAMETERS

	coord		Specifies a texture coordinate. Must be one of GL_S, GL_T, GL_R, or GL_Q.
	pname		Specifies the symbolic name of the texture-coordinate generation function. Must be GL_TEXTURE_GEN_MODE.
	param		Specifies a single-valued texture generation parameter, one of GL_OBJECT_LINEAR, GL_EYE_LINEAR, or GL_SPHERE_MAP.

C SPECIFICATION

void glTexGendv( GLenum coord,
GLenum pname,

const GLdouble *params )

void glTexGenfv( GLenum coord,

	GLenum pname,
	const GLfloat *params )

void glTexGeniv( GLenum coord,

	GLenum pname,
	const GLint *params )

PARAMETERS

	coord		Specifies a texture coordinate. Must be one of GL_S, GL_T, GL_R, or GL_Q.
	pname		Specifies the symbolic name of the texture-coordinate generation function or function parameters. Must be GL_TEXTURE_GEN_MODE, GL_OBJECT_PLANE, or GL_EYE_PLANE.
	params		Specifies a pointer to an array of texture generation parameters. If pname is GL_TEXTURE_GEN_MODE, then the array must contain a single symbolic constant, one of GL_OBJECT_LINEAR, GL_EYE_LINEAR, or GL_SPHERE_MAP. Otherwise, params holds the coefficients for the texture-coordinate generation function specified by pname.

DESCRIPTION

glTexGen selects a texture-coordinate generation function or supplies coefficients for one of the functions. coord names one of the (s, t, r, q) texture coordinates; it must be one of the symbols GL_S, GL_T, GL_R, or GL_Q. pname must be one of three symbolic constants: GL_TEXTURE_GEN_MODE, GL_OBJECT_PLANE, or GL_EYE_PLANE. If pname is GL_TEXTURE_GEN_MODE, then params chooses a mode, one of GL_OBJECT_LINEAR, GL_EYE_LINEAR, or GL_SPHERE_MAP. If pname is either GL_OBJECT_PLANE or GL_EYE_PLANE, params contains coefficients for the corresponding texture generation function.

If the texture generation function is GL_OBJECT_LINEAR, the function

$g ~=~ p sub 1^x sub o ~+~ p sub 2^y sub o ~+~ p sub 3^z sub o ~+~ p sub 4^w sub o$

is used, where $g$ is the value computed for the coordinate named in coord, $p sub 1$, $p sub 2$, $p sub 3$, and $p sub 4$ are the four values supplied in params, and $x sub o$, $y sub o$, $z sub o$, and $w sub o$ are the object coordinates of the vertex. This function can be used, for example, to texture-map terrain using sea level as a reference plane (defined by $p sub 1$, $p sub 2$, $p sub 3$, and $p sub 4$). The altitude of a terrain vertex is computed by the GL_OBJECT_LINEAR coordinate generation function as its distance from sea level; that altitude can then be used to index the texture image to map white snow onto peaks and green grass onto foothills.

If the texture generation function is GL_EYE_LINEAR, the function

$g ~=~ p sub 1 sup prime ^x sub e ~+~ p sub 2 sup prime ^y sub e ~+~ p sub 3 sup prime ^z sub e ~+~ p sub 4 sup prime ^w sub e$

is used, where

$( p sub 1 sup prime ~~p sub 2 sup prime~~p sub 3 sup prime~~ { p sub 4 sup prime}) ~=~ ( p sub 1~~ p sub 2~~ p sub 3~~ p sub 4 ) ~M sup -1$

and $x sub e$, $y sub e$, $z sub e$, and $w sub e$ are the eye coordinates of the vertex, $p sub 1$, $p sub 2$, $p sub 3$, and $p sub 4$ are the values supplied in params, and $M$ is the modelview matrix when glTexGen is invoked. If $M$ is poorly conditioned or singular, texture coordinates generated by the resulting function may be inaccurate or undefined.

Note that the values in params define a reference plane in eye coordinates. The modelview matrix that is applied to them may not be the same one in effect when the polygon vertices are transformed. This function establishes a field of texture coordinates that can produce dynamic contour lines on moving objects.

If pname is GL_SPHERE_MAP and coord is either GL_S or GL_T, $s$ and $t$ texture coordinates are generated as follows. Let u be the unit vector pointing from the origin to the polygon vertex (in eye coordinates). Let n sup prime be the current normal, after transformation to eye coordinates. Let

$f ~=~ ( f sub x~~f sub y~~f sub z ) sup T$ be the reflection vector such that

$f ~=~ u ~-~ 2 n sup prime n sup prime sup T u$

Finally, let $ m ~=~ 2 sqrt { f sub x sup {~2} ~+~ f sub y sup {~2} ~+~ (f sub z ~+~ 1 ) sup 2}$. Then the values assigned to the $s$ and $t$ texture coordinates are

$s ~=~ f sub x over m ~+~ 1 over 2$

$t ~=~ f sub y over m ~+~ 1 over 2$

To enable or disable a texture-coordinate generation function, call glEnable or glDisable with one of the symbolic texture-coordinate names (GL_TEXTURE_GEN_S, GL_TEXTURE_GEN_T, GL_TEXTURE_GEN_R, or GL_TEXTURE_GEN_Q) as the argument. When enabled, the specified texture coordinate is computed according to the generating function associated with that coordinate. When disabled, subsequent vertices take the specified texture coordinate from the current set of texture coordinates. Initially, all texture generation functions are set to GL_EYE_LINEAR and are disabled. Both $s$ plane equations are (1, 0, 0, 0), both $t$ plane equations are (0, 1, 0, 0), and all $r$ and $q$ plane equations are (0, 0, 0, 0).

When the GL_ARB_multitexture extension is supported, glTexGen set the texture generation parameters for the currently active texture unit, selected with glActiveTextureARB.

ERRORS

GL_INVALID_ENUM is generated when coord or pname is not an accepted defined value, or when pname is GL_TEXTURE_GEN_MODE and params is not an accepted defined value.

GL_INVALID_ENUM is generated when pname is GL_TEXTURE_GEN_MODE, params is GL_SPHERE_MAP, and coord is either GL_R or GL_Q.

GL_INVALID_OPERATION is generated if glTexGen is executed between the execution of glBegin and the corresponding execution of glEnd.

ASSOCIATED GETS

glGetTexGen
glIsEnabled with argument GL_TEXTURE_GEN_S
glIsEnabled with argument GL_TEXTURE_GEN_T
glIsEnabled with argument GL_TEXTURE_GEN_R
glIsEnabled with argument GL_TEXTURE_GEN_Q

Opportunity

Personal Opportunity - Free software gives you access to billions of dollars of software at no cost. Use this software for your business, personal use or to develop a profitable skill. Access to source code provides access to a level of capabilities/information that companies protect though copyrights. Open source is a core component of the Internet and it is available to you. Leverage the billions of dollars in resources and capabilities to build a career, establish a business or change the world. The potential is endless for those who understand the opportunity.

Business Opportunity - Goldman Sachs, IBM and countless large corporations are leveraging open source to reduce costs, develop products and increase their bottom lines. Learn what these companies know about open source and how open source can give you the advantage.

Free Software

Free Software provides computer programs and capabilities at no cost but more importantly, it provides the freedom to run, edit, contribute to, and share the software. The importance of free software is a matter of access, not price. Software at no cost is a benefit but ownership rights to the software and source code is far more significant.

Free Office Software - The Libre Office suite provides top desktop productivity tools for free. This includes, a word processor, spreadsheet, presentation engine, drawing and flowcharting, database and math applications. Libre Office is available for Linux or Windows.

Free Books

The Free Books Library is a collection of thousands of the most popular public domain books in an online readable format. The collection includes great classical literature and more recent works where the U.S. copyright has expired. These books are yours to read and use without restrictions.

Source Code - Want to change a program or know how it works? Open Source provides the source code for its programs so that anyone can use, modify or learn how to write those programs themselves. Visit the GNU source code repositories to download the source.

Education

Study at Harvard, Stanford or MIT - Open edX provides free online courses from Harvard, MIT, Columbia, UC Berkeley and other top Universities. Hundreds of courses for almost all major subjects and course levels. Open edx also offers some paid courses and selected certifications.

Linux Manual Pages - A man or manual page is a form of software documentation found on Linux/Unix operating systems. Topics covered include computer programs (including library and system calls), formal standards and conventions, and even abstract concepts.