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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

Beschreibung

Bezieher unterstützen einen Weg um mit ganzrationalen Funktionen Vertexe, Normalen, Textur-Koordinaten und Farben zu erzeugen. Die von den Evelatoren stammenden Werte, werden zu weitern OpenGL Verarbeitungs stufen gesendet, als ob sie von glVertex, glNormal, glTexCoord und glColor Befehlen kommen würden. Der einzigste Unterschied besteht darin das die aktuelle Normale, Texturkoordinate oder Farbe nicht verändert wird.

Alle polynäre oder ganz rational polymäre "splines" von beliebigen Grades(bis zu dem maximalen Grad den die OpenGL Inmplementation unterstützt) können mit Evaluatoren beschrieben werden. Dies beinhalet fast sämtliche Oberflächen die von Computer Grafiken verwendet werden, inklusive B-spline Oberflächen, NURBS Oberflächen, Bezieher Oberflächen und so weiter.

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)

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