Linux Manual Pages

Free Software * Books

Source Code

Free Media

Linux

GLMAP2

HOME

GLMAP2

NAME
C SPECIFICATION
PARAMETERS
DESCRIPTION
NOTES
ERRORS
ASSOCIATED GETS
SEE ALSO

NAME

glMap2d, glMap2f − define a two-dimensional evaluator

C SPECIFICATION

void glMap2d( GLenum target,

	GLdouble u1,
	GLdouble u2,
	GLint ustride,
	GLint uorder,
	GLdouble v1,
	GLdouble v2,
	GLint vstride,
	GLint vorder,
	const GLdouble *points )

void glMap2f( GLenum target,

	GLfloat u1,
	GLfloat u2,
	GLint ustride,
	GLint uorder,
	GLfloat v1,
	GLfloat v2,
	GLint vstride,
	GLint vorder,
	const GLfloat *points )

PARAMETERS

	target		Specifies the kind of values that are generated by the evaluator. Symbolic constants GL_MAP2_VERTEX_3, GL_MAP2_VERTEX_4, GL_MAP2_INDEX, GL_MAP2_COLOR_4, GL_MAP2_NORMAL, GL_MAP2_TEXTURE_COORD_1, GL_MAP2_TEXTURE_COORD_2, GL_MAP2_TEXTURE_COORD_3, and GL_MAP2_TEXTURE_COORD_4 are accepted.
	u1, u2		Specify a linear mapping of $u$, as presented to glEvalCoord2, to $u hat$, one of the two variables that are evaluated by the equations specified by this command. Initially, u1 is 0 and u2 is 1.
	ustride		Specifies the number of floats or doubles between the beginning of control point $R sub ij$ and the beginning of control point $R sub { (i+1) j }$, where $i$ and $j$ are the $u$ and $v$ control point indices, respectively. This allows control points to be embedded in arbitrary data structures. The only constraint is that the values for a particular control point must occupy contiguous memory locations. The initial value of ustride is 0.
	uorder		Specifies the dimension of the control point array in the $u$ axis. Must be positive. The initial value is 1.
	v1, v2		Specify a linear mapping of $v$, as presented to glEvalCoord2, to $v hat$, one of the two variables that are evaluated by the equations specified by this command. Initially, v1 is 0 and v2 is 1.
	vstride		Specifies the number of floats or doubles between the beginning of control point $R sub ij$ and the beginning of control point $R sub { i (j+1) }$, where $i$ and $j$ are the $u$ and $v$ control point indices, respectively. This allows control points to be embedded in arbitrary data structures. The only constraint is that the values for a particular control point must occupy contiguous memory locations. The initial value of vstride is 0.
	vorder		Specifies the dimension of the control point array in the $v$ axis. Must be positive. The initial value is 1.
	points		Specifies a pointer to the array of control points.

DESCRIPTION

Evaluators provide a way to use polynomial or rational polynomial mapping to produce vertices, normals, texture coordinates, and colors. The values produced by an evaluator are sent on to further stages of GL processing just as if they had been presented using glVertex, glNormal, glTexCoord, and glColor commands, except that the generated values do not update the current normal, texture coordinates, or color.

All polynomial or rational polynomial splines of any degree (up to the maximum degree supported by the GL implementation) can be described using evaluators. These include almost all surfaces used in computer graphics, including B-spline surfaces, NURBS surfaces, Bezier surfaces, and so on.

Evaluators define surfaces based on bivariate Bernstein polynomials. Define $p ( u hat , v hat ) $ as

where $R sub ij$ is a control point, $B sub i sup n ( u hat )$ is the $i$th Bernstein polynomial of degree
$n$ (uorder = $n ~+~ 1$)

and $B sub j sup m ( v hat )$ is the $j$th Bernstein polynomial of degree $m$ (vorder = $m ~+~ 1$)

Recall that

$0 sup 0 ~==~ 1 $ and $ left ( ^ down 20 {cpile { n above 0 }} ~^ right ) ~~==~~ 1 $

glMap2 is used to define the basis and to specify what kind of values are produced. Once defined, a map can be enabled and disabled by calling glEnable and glDisable with the map name, one of the nine predefined values for target, described below. When glEvalCoord2 presents values $u$ and $v$, the bivariate Bernstein polynomials are evaluated using $u hat$ and $v hat$, where

$u hat ~~=~~ {u ~-~ "u1"} over {"u2" ~-~ "u1"}$

$v hat ~~=~~ {v ~-~ "v1"} over {"v2" ~-~ "v1"}$

target is a symbolic constant that indicates what kind of control points are provided in points, and what output is generated when the map is evaluated. It can assume one of nine predefined values:

	GL_MAP2_VERTEX_3		Each control point is three floating-point values representing $x$, $y$, and $z$. Internal glVertex3 commands are generated when the map is evaluated.
	GL_MAP2_VERTEX_4		Each control point is four floating-point values representing $x$, $y$, $z$, and $w$. Internal glVertex4 commands are generated when the map is evaluated.
	GL_MAP2_INDEX		Each control point is a single floating-point value representing a color index. Internal glIndex commands are generated when the map is evaluated but the current index is not updated with the value of these glIndex commands.
	GL_MAP2_COLOR_4		Each control point is four floating-point values representing red, green, blue, and alpha. Internal glColor4 commands are generated when the map is evaluated but the current color is not updated with the value of these glColor4 commands.
	GL_MAP2_NORMAL		Each control point is three floating-point values representing the $x$, $y$, and $z$ components of a normal vector. Internal glNormal commands are generated when the map is evaluated but the current normal is not updated with the value of these glNormal commands.
	GL_MAP2_TEXTURE_COORD_1		Each control point is a single floating-point value representing the $s$ texture coordinate. Internal

glTexCoord1 commands are generated when the map is evaluated but the current texture coordinates are not updated with the value of these glTexCoord commands.

GL_MAP2_TEXTURE_COORD_2

Each control point is two floating-point values representing the $s$ and $t$ texture coordinates. Internal

glTexCoord2 commands are generated when the map is evaluated but the current texture coordinates are not updated with the value of these glTexCoord commands.

	GL_MAP2_TEXTURE_COORD_3		Each control point is three floating-point values representing the $s$, $t$, and $r$ texture coordinates. Internal glTexCoord3 commands are generated when the map is evaluated but the current texture coordinates are not updated with the value of these glTexCoord commands.
	GL_MAP2_TEXTURE_COORD_4		Each control point is four floating-point values representing the $s$, $t$, $r$, and $q$ texture coordinates. Internal

glTexCoord4 commands are generated when the map is evaluated but the current texture coordinates are not updated with the value of these glTexCoord commands.

ustride, uorder, vstride, vorder, and points define the array addressing for accessing the control points. points is the location of the first control point, which occupies one, two, three, or four contiguous memory locations, depending on which map is being defined. There are $ "uorder" ~times~ "vorder" $ control points in the array. ustride specifies how many float or double locations are skipped to advance the internal memory pointer from control point $R sub {i j} $ to control point $R sub {(i+1) j} $. vstride specifies how many float or double locations are skipped to advance the internal memory pointer from control point $R sub {i j} $ to control point $R sub {i (j+1) } $.

NOTES

As is the case with all GL commands that accept pointers to data, it is as if the contents of points were copied by glMap2 before glMap2 returns. Changes to the contents of points have no effect after glMap2 is called.

Initially, GL_AUTO_NORMAL is enabled. If GL_AUTO_NORMAL is enabled, normal vectors are generated when either GL_MAP2_VERTEX_3 or GL_MAP2_VERTEX_4 is used to generate vertices.

ERRORS

GL_INVALID_ENUM is generated if target is not an accepted value.

GL_INVALID_VALUE is generated if u1 is equal to u2, or if v1 is equal to v2.

GL_INVALID_VALUE is generated if either ustride or vstride is less than the number of values in a control point.

GL_INVALID_VALUE is generated if either uorder or vorder is less than 1 or greater than the return value of GL_MAX_EVAL_ORDER.

GL_INVALID_OPERATION is generated if glMap2 is executed between the execution of glBegin and the corresponding execution of glEnd.

When the GL_ARB_multitexture extension is supported, GL_INVALID_OPERATION is generated if glMap2 is called and the value of GL_ACTIVE_TEXTURE_ARB is not GL_TEXTURE0_ARB.

ASSOCIATED GETS

glGetMap
glGet with argument GL_MAX_EVAL_ORDER
glIsEnabled with argument GL_MAP2_VERTEX_3
glIsEnabled with argument GL_MAP2_VERTEX_4
glIsEnabled with argument GL_MAP2_INDEX
glIsEnabled with argument GL_MAP2_COLOR_4
glIsEnabled with argument GL_MAP2_NORMAL
glIsEnabled with argument GL_MAP2_TEXTURE_COORD_1
glIsEnabled with argument GL_MAP2_TEXTURE_COORD_2
glIsEnabled with argument GL_MAP2_TEXTURE_COORD_3
glIsEnabled with argument GL_MAP2_TEXTURE_COORD_4

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.