NAME

       glDrawElementsIndirect - render indexed primitives from array data, taking parameters from
       memory

C SPECIFICATION

       void glDrawElementsIndirect(GLenum mode, GLenum type, const void *indirect);

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 the draw parameters.

DESCRIPTION

       glDrawElementsIndirect specifies multiple indexed geometric primitives with very few
       subroutine calls.  glDrawElementsIndirect behaves similarly to
       glDrawElementsInstancedBaseVertexBaseInstance(), execpt that the parameters to
       glDrawElementsInstancedBaseVertexBaseInstance() are stored in memory at the address given
       by indirect.

       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;

               void glDrawElementsIndirect(GLenum mode, GLenum type, const void * indirect)
               {
                   const DrawElementsIndirectCommand *cmd  = (const DrawElementsIndirectCommand *)indirect;
                   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_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(),

COPYRIGHT

       Copyright © 2010 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