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

void glEvalMesh1( GLenummode, GLinti1, GLinti2)

modeIn glEvalMesh1, specifies whether to compute a one-dimensional mesh of points or lines. Symbolic constants GL_POINT and GL_LINE are accepted.i1,i2Specify the first and last integer values for grid domain variable i.

void glEvalMesh2( GLenummode, GLinti1, GLinti2, GLintj1, GLintj2)

modeIn 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.i1,i2Specify the first and last integer values for grid domain variable i.j1,j2Specify the first and last integer values for grid domain variable j.

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.modedetermines 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 · du + u1) glEnd(); where du = (u2-u1)/n and n, u1, and u2 are the arguments to the most recent glMapGrid1 command. type is GL_POINT ifmodeis GL_POINT, or GL_LINES ifmodeis GL_LINE. The one absolute numeric requirement is that if i = n, then the value computed from i·du + u1 is exactly u2. In the two-dimensional case, glEvalMesh2, let du = (u2-u1)/n dv = (v2-v1)/m where n, u1, u2, m, v1, and v2 are the arguments to the most recent glMapGrid2 comand. Then, ifmodeis 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·du + u1, j·dv + v1); glEvalCoord2(i·du + u1, (j+1)·dv + v1); } glEnd(); } Ifmodeis 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·du + u1, j·dv + v1); glEnd(); } for (i =i1; i <=i2; i += 1) { glBegin(GL_LINE_STRIP); for (j =j1; j <=j1; j += 1) glEvalCoord2(i·du + u1, j·dv + v1); glEnd(); } And finally, ifmodeis 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·du + u1, j·dv + v1); } } glEnd(); In all three cases, the only absolute numeric requirements are that if i = n, then the value computed from i·du + u1 is exactly u2, and if j = m, then the value computed from j·dv + v1 is exactly v2.

GL_INVALID_ENUM is generated ifmodeis not an accepted value. GL_INVALID_OPERATION is generated if glEvalMesh is called between a call to glBegin and the corresponding call to 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

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Fri Dec 6 11:18:03 EST 1996
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