glDrawElementsIndirect - OpenGL ES 3.1 Reference Pages

## 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_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, except that the parameters to glDrawElementsInstanced are stored in memory at the address given by `indirect` and the ith element transferred by the corresponding draw call will be taken from element `indices`[i] + `baseVertex` of each enabled array. If the resulting value is larger than the maximum value representable by `type`, it is as if the calculation were upconverted to 32-bit unsigned integers (with wrapping on overflow conditions). The operation is undefined if the sum would be negative.It also supports the addition of a value baseVertex to each index.

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

        typedef  struct {
            uint  count;
            uint  instanceCount;
            uint  firstIndex;
            int   baseVertex;
            uint  reservedMustBeZero;
        } DrawElementsIndirectCommand;

`glDrawElementsIndirect` is equivalent to:

        void glDrawElementsIndirect(GLenum mode, GLenum type, const void * indirect)
        {
            const DrawElementsIndirectCommand *cmd  = (const DrawElementsIndirectCommand *)indirect;
            glDrawElementsInstancedBaseVertex(mode,
                                              cmd->count,
                                              type,
                                              cmd->firstIndex * size-of-type,
                                              cmd->instanceCount,
                                              cmd->baseVertex);
        }

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

`glDrawElementsInstancedBaseVertex` isn't actually present in OpenGL ES, but is used to describe this functionality.

## 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

| OpenGL ES API Version
--- | ---
Function Name | 2.0 | 3.0 | 3.1
`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/.