Parameters

Parameters

Description

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:

glBegin( type );
for ( i = i1; i <= i2; i += 1 )
   glEvalCoord1( 
   		      
		      
		          
		              i
			      ·
			      Δ
		              u
		          
		          +
		          
		              u
		              1
		          
		      
		   );
glEnd();
            

where

and n, u 1 , and 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 i = n , then the value computed from i · Δ u + u 1 is exactly u 2 .

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

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

for ( j = j1; j < j2; j += 1 ) {
   glBegin( GL_QUAD_STRIP );
   for ( i = i1; i <= i2; i += 1 ) {
      glEvalCoord2( 
			
		        
			    
			        i
				·
			        Δ
		                u
			    
		            +
		            
		                u
		                1
		            
			    ,
			    
			    
			        j
				·
			        Δ
		                v

			    
		            +
		            
		                v
		                1
		            
			
		     );
      glEvalCoord2( 
			
		        
			    
			        i
				·
			        Δ
		                u
			    
		            +
		            
		                u
		                1
		            
			    ,
			    
			    
			        
				    
				        
			                    j
				            +
			                    1
				        
				    
				
				·
			        Δ
		                v
			    
		            +
		            
		                v
		                1
		            
			
		     );
   }
   glEnd();
}
            

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

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

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

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

glBegin( GL_POINTS );
for ( j = j1; j <= j2; j += 1 )
   for ( i = i1; i <= i2; i += 1 )
      glEvalCoord2( 
			
		        
			    
			        i
				·
			        Δ
		                u
			    
		            +
		            
		                u
		                1
		            
			    ,
			    
			    
			        j
				·
			        Δ
		                v
			    
		            +
		            
		                v
		                1
		            
			
		     );
glEnd();
            

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

Errors

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.

Associated Gets

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

See Also

glBegin, glEvalCoord, glEvalPoint, glMap1, glMap2, glMapGrid

Copyright

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/.