glMap2

NAME

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

DESCRIPTION

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(û, ˆv) as

p(û, ˆv) = SUM ( SUM ( Bⁿ_i(û) B^m_j(ˆv)R_ij ))

where R_ij is a control point, Bⁿ_i(û) is the i^th Bernstein polynomial of degree n (uorder = n+1)

Bⁿ_i(û) = (ⁿ_i) ûⁱ (1 - û)^{n - i}

and B^m_j(ˆv) is the j^th Bernstein polynomial of degree m (vorder = m+1)

B^m_j(ˆv) = (^m_j) ˆv^j (1 - ˆv)^{m - j}

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 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 û and ˆv, where

û = (u - u1) / (u2 - u1)

ˆv = (v - v1) / (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.

NOTES

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_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.

ASSOCIATED GETS

SEE ALSO