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GLMULTIDRAWELEMENTSI(3G)	 OpenGL Manual	      GLMULTIDRAWELEMENTSI(3G)

NAME
       glMultiDrawElementsIndirect - render indexed primitives from array
       data, taking parameters from memory

C SPECIFICATION
       void glMultiDrawElementsIndirect(GLenum mode, GLenum type,
					const void *indirect,
					GLsizei drawcount, GLsizei stride);

PARAMETERS
       mode
	   Specifies what kind of primitives to render. Symbolic constants
	   GL_POINTS, GL_LINE_STRIP, GL_LINE_LOOP, GL_LINES,
	   GL_LINE_STRIP_ADJACENCY, GL_LINES_ADJACENCY, GL_TRIANGLE_STRIP,
	   GL_TRIANGLE_FAN, GL_TRIANGLES, GL_TRIANGLE_STRIP_ADJACENCY,
	   GL_TRIANGLES_ADJACENCY, and GL_PATCHES are accepted.

       type
	   Specifies the type of data in the buffer bound to the
	   GL_ELEMENT_ARRAY_BUFFER binding.

       indirect
	   Specifies the address of a structure containing an array of draw
	   parameters.

       drawcount
	   Specifies the number of elements in the array addressed by
	   indirect.

       stride
	   Specifies the distance in basic machine units between elements of
	   the draw parameter array.

DESCRIPTION
       glMultiDrawElementsIndirect specifies multiple indexed geometric
       primitives with very few subroutine calls.  glMultiDrawElementsIndirect
       behaves similarly to a multitude of calls to
       glDrawElementsInstancedBaseVertexBaseInstance(), execpt that the
       parameters to glDrawElementsInstancedBaseVertexBaseInstance() are
       stored in an array in memory at the address given by indirect,
       separated by the stride, in basic machine units, specified by stride.
       If stride is zero, then the array is assumed to be tightly packed in
       memory.

       The parameters addressed by indirect are packed into a structure that
       takes the form (in C):

	       typedef	struct {
		   uint	 count;
		   uint	 primCount;
		   uint	 firstIndex;
		   uint	 baseVertex;
		   uint	 baseInstance;
	       } DrawElementsIndirectCommand;

       A single call to glMultiDrawElementsIndirect is equivalent, assuming no
       errors are generated to:

	       GLsizei n;
	       for (n = 0; n < drawcount; n++)
	       {
		   const DrawElementsIndirectCommand  *cmd;
		   if (stride != 0)
		   {
		       cmd = (const DrawElementsIndirectCommand	 *)((uintptr)indirect + n * stride);
		   }
		   else
		   {
		       cmd = (const DrawElementsIndirectCommand	 *)indirect + n;
		   }

		   glDrawElementsInstancedBaseVertexBaseInstance(mode,
								 cmd->count,
								 type,
								 cmd->firstIndex + size-of-type,
								 cmd->primCount,
								 cmd->baseVertex,
								 cmd->baseInstance);
	       }

       If a buffer is bound to the GL_DRAW_INDIRECT_BUFFER binding at the time
       of a call to glDrawElementsIndirect, indirect is interpreted as an
       offset, in basic machine units, into that buffer and the parameter data
       is read from the buffer rather than from client memory.

       Note that indices stored in client memory are not supported. If no
       buffer is bound to the GL_ELEMENT_ARRAY_BUFFER binding, an error will
       be generated.

       The results of the operation are undefined if the reservedMustBeZero
       member of the parameter structure is non-zero. However, no error is
       generated in this case.

       Vertex attributes that are modified by glDrawElementsIndirect have an
       unspecified value after glDrawElementsIndirect returns. Attributes that
       aren't modified remain well defined.

NOTES
       The baseInstance member of the DrawElementsIndirectCommand structure is
       defined only if the GL version is 4.2 or greater. For versions of the
       GL less than 4.2, this parameter is present but is reserved and should
       be set to zero. On earlier versions of the GL, behavior is undefined if
       it is non-zero.

ERRORS
       GL_INVALID_ENUM is generated if mode is not an accepted value.

       GL_INVALID_VALUE is generated if stride is not a multiple of four.

       GL_INVALID_VALUE is generated if drawcount is negative.

       GL_INVALID_OPERATION is generated if no buffer is bound to the
       GL_ELEMENT_ARRAY_BUFFER binding, or if such a buffer's data store is
       currently mapped.

       GL_INVALID_OPERATION is generated if a non-zero buffer object name is
       bound to an enabled array or to the GL_DRAW_INDIRECT_BUFFER binding and
       the buffer object's data store is currently mapped.

       GL_INVALID_OPERATION is generated if a geometry shader is active and
       mode is incompatible with the input primitive type of the geometry
       shader in the currently installed program object.

       GL_INVALID_OPERATION is generated if mode is GL_PATCHES and no
       tessellation control shader is active.

SEE ALSO
       glDrawArrays(), glDrawArraysInstanced(), glDrawArraysIndirect(),
       glDrawElements(), glDrawRangeElements(), glDrawElementsIndirect(),
       glMultiDrawArraysIndirect()

COPYRIGHT
       Copyright © 2010-2012 Khronos Group. This material may be distributed
       subject to the terms and conditions set forth in the Open Publication
       License, v 1.0, 8 June 1999.  http://opencontent.org/openpub/.

AUTHORS
       opengl.org

opengl.org			  03/16/2013	      GLMULTIDRAWELEMENTSI(3G)
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