Method GL.glEvalMesh2()

Method glEvalMesh2

void glEvalMesh2(int mode, int i1, int i2, int j1, int j2)

Description

glMapGrid and glEvalMesh1 and glEvalMesh2 are used in tandem to efficiently generate and evaluate a series of evenly-spaced map domain values. glEvalMesh1 and glEvalMesh2 steps through the integer domain of a one- or two-dimensional grid, whose range is the domain of the evaluation maps specified by glMap1 and glMap2. mode determines whether the resulting vertices are connected as points, lines, or filled polygons.

In the one-dimensional case, glEvalMesh1, the mesh is generated as if the following code fragment were executed: .nf

glBegin (type); for (i = i1; i <= i2; i += 1) glEvalCoord1(i . DELTA u + u sub 1) glEnd();

.fi where .sp .nf DELTA u = (u - u ) / 1 2 1 .fi .sp .nf and n, u, and u are the arguments to the most recent 1 2

.fi glMapGrid1 command. type is GL_POINTS if mode is GL_POINT, or GL_LINES if mode is GL_LINE.

The one absolute numeric requirement is that if i = n, then the value computed from .nf

i . DELTA u + u

is exactly u. .fi 1 2

In the two-dimensional case, glEvalMesh2, let .sp .nf DELTA u = (u - u )/n 2 1

DELTA v = (v - v )/m, 2 1

where n, u , u , m, v , and v 1 2 1 2 .fi are the arguments to the most recent glMapGrid2 command. Then, if mode is GL_FILL, the glEvalMesh2 command is equivalent to: .nf

for (j = j1; j < j2; j += 1) { glBegin (GL_QUAD_STRIP); for (i = i1; i <= i2; i += 1) { glEvalCoord2(i . DELTA u + u , j . DELTA v + v ); 1 1 glEvalCoord2(i . DELTA u + u , (j+1) . DELTA v + v ); 1 1 } glEnd(); }

.fi

If mode is GL_LINE, then a call to glEvalMesh2 is equivalent to: .nf

for (j = j1; j <= j2; j += 1) { glBegin(GL_LINE_STRIP); for (i = i1; i <= i2; i += 1) glEvalCoord2(i . DELTA u + u , j . DELTA v + v ); 1 1 glEnd(); } for (i = i1; i <= i2; i += 1) { glBegin(GL_LINE_STRIP); for (j = j1; j <= j1; j += 1) glEvalCoord2)(i . DELTA u + u , j . DELTA v + v ); 1 1 glEnd(); }

.fi

And finally, if mode is GL_POINT, then a call to glEvalMesh2 is equivalent to: .nf

glBegin (GL_POINTS); for (j = j1; j <= j2; j += 1) { for (i = i1; i <= i2; i += 1) { glEvalCoord2(i . DELTA u + u , j . DELTA v + v ); 1 1 } } glEnd(); .fi

In all three cases, the only absolute numeric requirements are that if i~=~n, then the value computed from .nf i . DELTA u + u is exactly u , 1 2 and if j~=~m, then the value computed from j . DELTA v + v is exactly v . 1 2

Parameter mode

In glEvalMesh1, specifies whether to compute a one-dimensional mesh of points or lines. Symbolic constants GL_POINT and GL_LINE are accepted.

Parameter i1

Specify the first and last integer values for grid domain variable i.

Parameter mode

In glEvalMesh2, specifies whether to compute a two-dimensional mesh of points, lines, or polygons. Symbolic constants GL_POINT, GL_LINE, and GL_FILL are accepted.

Parameter i1

Specify the first and last integer values for grid domain variable i.

Parameter j1

Specify the first and last integer values for grid domain variable j.

Throws

GL_INVALID_ENUM is generated if mode is not an accepted value.

GL_INVALID_OPERATION is generated if glEvalMesh1 and glEvalMesh2 is executed between the execution of glBegin and the corresponding execution of glEnd.