glMap2

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glMap2


Name

glMap2 - definiert einen 2 demensionalen Bezieher


Delphi-Spezifikation

procedure glMap2d(target: TGLenum; u1: TGLdouble; u2: TGLdouble; ustride: TGLint; 
                  uorder: TGLint; v1: TGLdouble; v2: TGLdouble; 
                  vstride: TGLint; vorder: TGLint; const points: PGLdouble);

procedure glMap2f(target: TGLenum; u1: TGLfloat; u2: TGLfloat; ustride: TGLint;
                  uorder: TGLint; v1: TGLfloat;  v2: TGLfloat; vstride: TGLint; 
                  vorder: TGLint; const points: PGLfloat);


Parameter

target Bestimmt den Typ der Werte die generiert werden sollen. Folgende symbolsiche Konstanden werden akzeptiert: 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, und GL_MAP2_TEXTURE_COORD_4
u1, u2 Specify a linear mapping of u, as presented to glEvalCoord2, 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, where i and j are the u and v control pointiindices, 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 ^, 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, 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 Ein Zeiger auf den Kontrollpunkt Array.


Beschreibung

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(^,^) as n m R R n m p(^,^) = i=0j=0Bi(^)Bj(^)Rij


where R is a control point, Bn(^) is the ith Bernstein polynomial of degree i n (uorder = n+1)

n (n ) i n-i Bi(^) = | |^ (1-^) (i ) and Bm(^) is the jth Bernstein polynomial of degree m (vorder = m+1)

m (m ) j m-j Bj(^) = | |^ (1-^) (j ) Recall that 0 (n ) 0 = 1 and | | = 1 ( 0 ) 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 ^ 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 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 uorderxvorder 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 specifies how many float or double locationsiarejskipped to advance the internal memory pointer from control point R to control point R . ij i(j+1)



Hinweise

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.



Fehlermeldungen

GL_INVALID_ENUM wird generiert wenn target nicht akzeptiert wird
GL_INVALID_VALUE wird geniert wenn u1 = u2 ist oder wenn v1 = v2 ist.
GL_INVALID_VALUE wird geniert wenn ustride oder vstride kleiner ist als die anzahl der Kontrollpunkte
GL_INVALID_VALUE wird geniert wenn ustride oder vstride kleiner als 1 oder größer als GL_MAX_EVAL_ORDER ist.
GL_INVALID_OPERATION wird generiert wenn glMap2 innerhalb eines glBegin-glEnd Blocks aufgerufen wird.


Zugehörige Wertrückgaben



Siehe auch

glBegin, glColor, glEnable, glEvalCoord, glEvalMesh, glEvalPoint, glMap1, glMapGrid, glNormal, glTexCoord, glVertex

Abgerufen von „https://wiki.delphigl.com/index.php?title=glMap2&oldid=7803“