glEvalMesh

glMapGrid and glEvalMesh are used in tandem to efficiently generate and evaluate a series of evenly-spaced map domain values. glEvalMesh 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:

where

and $\mathit{n}$ , ${\mathit{u}}_1$ , and ${\mathit{u}}_2$ 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 .

The one absolute numeric requirement is that if $\mathit{i}=\mathit{n}$ , then the value computed from $\mathit{i}\mathit{u}+{\mathit{u}}_1$ is exactly ${\mathit{u}}_2$ .

In the two-dimensional case, glEvalMesh2 , let .cp

where $\mathit{n}$ , ${\mathit{u}}_1$ , ${\mathit{u}}_2$ , $\mathit{m}$ , ${\mathit{v}}_1$ , and ${\mathit{v}}_2$ are the arguments to the most recent glMapGrid2 command. Then, if mode is GL_FILL , the glEvalMesh2 command is equivalent to:

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

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

In all three cases, the only absolute numeric requirements are that if $\mathit{i}=\mathit{n}$ , then the value computed from $\mathit{i}\mathit{u}+{\mathit{u}}_1$ is exactly ${\mathit{u}}_2$ , and if $\mathit{j}=\mathit{m}$ , then the value computed from $\mathit{j}\mathit{v}+{\mathit{v}}_1$ is exactly ${\mathit{v}}_2$ .

GL_INVALID_ENUM is generated if mode is not an accepted value.

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

glGet with argument GL_MAP1_GRID_DOMAIN

glGet with argument GL_MAP2_GRID_DOMAIN

glGet with argument GL_MAP1_GRID_SEGMENTS

glGet with argument GL_MAP2_GRID_SEGMENTS

glBegin , glEvalCoord , glEvalPoint , glMap1 , glMap2 , glMapGrid

Copyright 1991-2006 Silicon Graphics, Inc. This document is licensed under the SGI Free Software B License. For details, see http://oss.sgi.com/projects/FreeB/ .