2010-2014
Khronos Group.
glDrawElementsIndirect
3G

# 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_TRIANGLE_STRIP`, `GL_TRIANGLE_FAN`, and `GL_TRIANGLES`, 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 glDrawElementsInstanced, execpt that the parameters to glDrawElementsInstanced 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  reservedMustBeZero;
            uint  reservedMustBeZero2;
        } DrawElementsIndirectCommand;

`glDrawElementsIndirect` is equivalent to:

        void glDrawElementsIndirect(GLenum mode, GLenum type, const void * indirect)
        {
            const DrawElementsIndirectCommand *cmd  = (const DrawElementsIndirectCommand *)indirect;
            glDrawElementsInstanced(mode,
                                    cmd->count,
                                    type,
                                    cmd->firstIndex + size-of-type,
                                    cmd->primCount);
        }

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 either of the `reservedMustBeZero` or `reservedMustBeZero2` members of the parameter structure are 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.

## 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.

## API Version Support

`glDrawElementsIndirect`

## See Also

glDrawArrays, glDrawArraysInstanced, glDrawArraysIndirect, glDrawElements, glDrawRangeElements,

## Copyright

Copyright 2010-2014 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/.