2012-2013
Khronos Group.
glMultiDrawArraysIndirect
3G

# glMultiDrawArraysIndirect

render multiple sets of primitives from array data, taking parameters from memory

## C Specification

                    void glMultiDrawArraysIndirect
                    GLenum mode
                    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.

`indirect`

  Specifies the address of an array of structures containing the draw parameters.

`drawcount`

  Specifies the the number of elements in the array of draw parameter structures.

`stride`

  Specifies the distance in basic machine units between elements of the draw parameter array.

## Description

`glMultiDrawArraysIndirect` specifies multiple geometric primitives with very few subroutine calls. `glMultiDrawArraysIndirect` behaves similarly to a multitude of calls to glDrawArraysInstancedBaseInstance, execept that the parameters to each call to glDrawArraysInstancedBaseInstance 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 an array of structures, each element of which takes the form (in C):

        typedef  struct {
            uint  count;
            uint  instanceCount;
            uint  first;
            uint  baseInstance;
        } DrawArraysIndirectCommand;

A single call to `glMultiDrawArraysIndirect` is equivalent, assuming no errors are generated to:

        GLsizei n;
        for (n = 0; n < drawcount; n++) {
            const DrawArraysIndirectCommand *cmd;
            if (stride != 0) {
                cmd = (const DrawArraysIndirectCommand  *)((uintptr)indirect + n * stride);
            } else  {
                cmd = (const DrawArraysIndirectCommand  *)indirect + n;
            }

            glDrawArraysInstancedBaseInstance(mode, cmd->first, cmd->count, cmd->instanceCount, cmd->baseInstance);
        }

If a buffer is bound to the `GL_DRAW_INDIRECT_BUFFER` binding at the time of a call to `glMultiDrawArraysIndirect`, `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.

In contrast to glDrawArraysInstancedBaseInstance, the `first` member of the parameter structure is unsigned, and out-of-range indices do not generate an error.

Vertex attributes that are modified by `glMultiDrawArraysIndirect` have an unspecified value after `glMultiDrawArraysIndirect` returns. Attributes that aren't modified remain well defined.

## Notes

The `baseInstance` member of the `DrawArraysIndirectCommand` 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.

`glMultiDrawArraysIndirect` is available only if the GL version is 4.3 or greater.

## 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 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, glDrawElements, glDrawRangeElements, glDrawArraysIndirect, glMultiDrawElementsIndirect

## Copyright

Copyright 2012-2013 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/.