2013
Khronos Group.
glMultiDrawElementsIndirect
3G

# 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  instanceCount;
            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->instanceCount,
                                                          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 2010-2013 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/.