fglMap2(3G)
fglMap2d, fglMap2f - define a two-dimensional evaluator
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NAME fglMap2d, fglMap2f - define a two-dimensional evaluator FORTRAN SPECIFICATION SUBROUTINE fglMap2d( INTEGER*4 target, REAL*4 u1, REAL*4 u2, INTEGER*4 ustride, INTEGER*4 uorder, REAL*4 v1, REAL*4 v2, INTEGER*4 vstride, INTEGER*4 vorder, CHARACTER*8 points ) SUBROUTINE fglMap2f( INTEGER*4 target, REAL*4 u1, REAL*4 u2, INTEGER*4 ustride, INTEGER*4 uorder, REAL*4 v1, REAL*4 v2, INTEGER*4 vstride, INTEGER*4 vorder, CHARACTER*8 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 fglEvalCoord2, to ^, 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 and the beginning of control point R , ij (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 fglEvalCoord2, to ^, 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 and the beginning of control point R , ij 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 fglVertex, fglNormal, fglTexCoord, and fglColor 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(^,^) as m n m n B (^) B (^) R p(^,^) = R i j ij R j = 0 i = 0 n where R is a control point, B (^) is the ith Bernstein polynomial of ij i degree n (uorder = n + 1) ( ) n n i n-i B (^) = | |^ (1-^) i (i ) m and B (^) is the jth Bernstein polynomial of degree m (vorder = m + 1) j ( ) m m j m-j B (^) = | |^ (1-^) j (j ) Recall that ( ) 0 n 0 = 1 and | | = 1 (0 ) fglMap2 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 fglEnable and fglDisable with the map name, one of the nine predefined values for target, described below. When fglEvalCoord2 presents values u and v, the bivariate Bernstein polynomials are evaluated using ^ and ^, where _______ ^ = u2 - u1 _______ ^ = 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 fglVertex3 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 fglVertex4 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 fglIndex commands are generated when the map is evaluated but the current index is not updated with the value of these fglIndex commands. GL_MAP2_COLOR_4 Each control point is four floating-point values representing red, green, blue, and alpha. Internal fglColor4 commands are generated when the map is evaluated but the current color is not updated with the value of these fglColor4 commands. GL_MAP2_NORMAL Each control point is three floating-point values representing the x, y, and z components of a normal vector. Internal fglNormal commands are generated when the map is evaluated but the current normal is not updated with the value of these fglNormal commands. GL_MAP2_TEXTURE_COORD_1 Each control point is a single floating-point value representing the s texture coordinate. Internal fglTexCoord1 commands are generated when the map is evaluated but the current texture coordinates are not updated with the value of these fglTexCoord commands. GL_MAP2_TEXTURE_COORD_2 Each control point is two floating-point values representing the s and t texture coordinates. Internal fglTexCoord2 commands are generated when the map is evaluated but the current texture coordinates are not updated with the value of these fglTexCoord commands. GL_MAP2_TEXTURE_COORD_3 Each control point is three floating-point values representing the s, t, and r texture coordinates. Internal fglTexCoord3 commands are generated when the map is evaluated but the current texture coordinates are not updated with the value of these fglTexCoord commands. GL_MAP2_TEXTURE_COORD_4 Each control point is four floating-point values representing the s, t, r, and q texture coordinates. Internal fglTexCoord4 commands are generated when the map is evaluated but the current texture coordinates are not updated with the value of these fglTexCoord 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 x 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 to control point R . vstride ij (i+1)j specifies how many float or double locations are skipped to advance the internal memory pointer from control point R to control point R . ij 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 fglMap2 before fglMap2 returns. Changes to the contents of points have no effect after fglMap2 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 fglMap2 is executed between the execution of fglBegin and the corresponding execution of fglEnd. ASSOCIATED GETS fglGetMap fglGet with argument GL_MAX_EVAL_ORDER fglIsEnabled with argument GL_MAP2_VERTEX_3 fglIsEnabled with argument GL_MAP2_VERTEX_4 fglIsEnabled with argument GL_MAP2_INDEX fglIsEnabled with argument GL_MAP2_COLOR_4 fglIsEnabled with argument GL_MAP2_NORMAL fglIsEnabled with argument GL_MAP2_TEXTURE_COORD_1 fglIsEnabled with argument GL_MAP2_TEXTURE_COORD_2 fglIsEnabled with argument GL_MAP2_TEXTURE_COORD_3 fglIsEnabled with argument GL_MAP2_TEXTURE_COORD_4 SEE ALSO fglBegin, fglColor, fglEnable, fglEvalCoord, fglEvalMesh, fglEvalPoint, fglMap1, fglMapGrid, fglNormal, fglTexCoord, fglVertex