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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 (C) 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				    06/10/2014			 GLMULTIDRAWELEMENTSI(3G)
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