glEvalMesh1(3gl)

1GLEVALMESH(3G)                                                  GLEVALMESH(3G)
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NAME

6       glEvalMesh1,  glEvalMesh2  -  compute a one- or two-dimensional grid of
7       points or lines
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9

C SPECIFICATION

11       void glEvalMesh1( GLenum mode,
12                         GLint i1,
13                         GLint i2 )
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15

PARAMETERS

17       mode  In glEvalMesh1, specifies whether to  compute  a  one-dimensional
18             mesh of points or lines.  Symbolic constants GL_POINT and GL_LINE
19             are accepted.
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21       i1, i2
22             Specify the first and last integer values for grid  domain  vari‐
23             able i.
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C SPECIFICATION

26       void glEvalMesh2( GLenum mode,
27                         GLint i1,
28                         GLint i2,
29                         GLint j1,
30                         GLint j2 )
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32

PARAMETERS

34       mode   In  glEvalMesh2,  specifies whether to compute a two-dimensional
35              mesh  of  points,  lines,  or  polygons.    Symbolic   constants
36              GL_POINT, GL_LINE, and GL_FILL are accepted.
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38       i1, i2 Specify  the first and last integer values for grid domain vari‐
39              able i.
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41       j1, j2 Specify the first and last integer values for grid domain  vari‐
42              able j.
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DESCRIPTION

45       glMapGrid and glEvalMesh are used in tandem to efficiently generate and
46       evaluate a series of evenly-spaced map domain values.  glEvalMesh steps
47       through  the  integer  domain  of a one- or two-dimensional grid, whose
48       range is the domain of the evaluation  maps  specified  by  glMap1  and
49       glMap2.   mode  determines whether the resulting vertices are connected
50       as points, lines, or filled polygons.
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52       In the one-dimensional case, glEvalMesh1, the mesh is generated  as  if
53       the following code fragment were executed:
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55              glBegin( type );
56              for ( i = i1; i <= i2; i += 1 )
57                 glEvalCoord1( i⋅Δu+u1 );
58              glEnd();

where

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61              Δu=(u2−u1)/n
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64and  n,  u1,  and  u2 are the arguments to the most recent glMapGrid1 command.

type is GL_POINTS if mode is GL_POINT, or GL_LINES if mode is GL_LINE.

66
67The one absolute numeric requirement is that if i=n, then the  value  computed
68from i⋅Δu+u1 is exactly u2.
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70In the two-dimensional case, glEvalMesh2, let
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72       Δu=(u2−u1)/n
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74       Δv=(v2−v1)/m,
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76where n, u1, u2, m, v1, and v2 are the arguments to the most recent glMapGrid2
77command.  Then, if mode is GL_FILL, the glEvalMesh2 command is equivalent to:
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79       for ( j = j1; j < j2; j += 1 ) {
80          glBegin( GL_QUAD_STRIP );
81          for ( i = i1; i <= i2; i += 1 ) {
82             glEvalCoord2( i⋅Δu+u1, j⋅Δv+v1 );
83             glEvalCoord2( i⋅Δu+u1, (j+1)⋅Δv+v1 );
84          }
85          glEnd();
86       }
87
88If mode is GL_LINE, then a call to glEvalMesh2 is equivalent to:
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90       for ( j = j1; j <= j2; j += 1 ) {
91          glBegin( GL_LINE_STRIP );
92          for ( i = i1; i <= i2; i += 1 )
93             glEvalCoord2( i⋅Δu+u1, j⋅Δv+v1 );
94          glEnd();
95       }
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97       for ( i = i1;  i <= i2; i += 1 ) {
98          glBegin( GL_LINE_STRIP );
99          for ( j = j1; j <= j1; j += 1 )
100             glEvalCoord2( i⋅Δu+u1, j⋅Δv+v1 );
101          glEnd();
102       }
103
104And finally, if mode is GL_POINT, then a call to glEvalMesh2 is equivalent to:
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106       glBegin( GL_POINTS );
107       for ( j = j1; j <= j2; j += 1 )
108          for ( i = i1; i <= i2; i += 1 )
109             glEvalCoord2( i⋅Δu+u1, j⋅Δv+v1 );
110       glEnd();
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112In all three cases, the only absolute numeric requirements are  that  if  i=n,
113then the value computed from i⋅Δu+u1 is exactly u2, and if j=m, then the value
114computed from j⋅Δv+v1 is exactly v2.
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ERRORS

117       GL_INVALID_ENUM is generated if mode is not an accepted value.
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119       GL_INVALID_OPERATION is generated if glEvalMesh is executed between the
120       execution of glBegin and the corresponding execution of glEnd.
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ASSOCIATED GETS

123       glGet with argument GL_MAP1_GRID_DOMAIN
124       glGet with argument GL_MAP2_GRID_DOMAIN
125       glGet with argument GL_MAP1_GRID_SEGMENTS
126       glGet with argument GL_MAP2_GRID_SEGMENTS
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