glEvalPoint.3G man page

glEvalPoint — generate and evaluate a single point in a mesh

C Specification

void glEvalPoint1(GLint i);

void glEvalPoint2(GLint i, GLint j);

Parameters

i

Specifies the integer value for grid domain variable i.

j

Specifies the integer value for grid domain variable j (glEvalPoint2 only).

Description

glMapGrid() and glEvalMesh() are used in tandem to efficiently generate and evaluate a series of evenly spaced map domain values. glEvalPoint can be used to evaluate a single grid point in the same gridspace that is traversed by glEvalMesh(). Calling glEvalPoint1 is equivalent to calling

glEvalCoord1( 
	          
     	          
     	              
     	                  i
     	                  ⋅
     	                  Δ
     	                  u
     	              
     	              +
     	              
     	                  u
     	                  1
     	              
     	          
               );

where Δ u = u 2 - u 1 n

and n, u 1, and u 2 are the arguments to the most recent glMapGrid1() command. 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, glEvalPoint2, let

Δ u = u 2 - u 1 n.PP Δ v = v 2 - v 1 m

where n, u 1, u 2, m, v 1, and v 2 are the arguments to the most recent glMapGrid2() command. Then the glEvalPoint2 command is equivalent to calling

glEvalCoord2( 
			
		        
			    
			        i
				⋅
			        Δ
		                u
			    
		            +
		            
		                u
		                1
		            
			    ,
			    
			    
			        j
				⋅
			        Δ
		                v

			    
		            +
		            
		                v
		                1
		            
			
		     );

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.

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

glEvalCoord(), glEvalMesh(), glMap1(), glMap2(), glMapGrid()

Authors

opengl.org

Referenced By

glEvalPoint1.3G(3) and glEvalPoint2.3G(3) are aliases of glEvalPoint.3G(3).

02/04/2016 opengl.org OpenGL Manual