GLAPI/glMultiDrawArraysIndirect

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glMultiDrawArraysIndirect
Core in version 4.4
Core since version 4.3
Core ARB extension ARB_multi_draw_indirect

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

Function Definition

 void glMultiDrawArraysIndirect(GLenum mode​, const void *indirect​, GLsizei drawcount​, GLsizei stride​);
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

glBindVertexArray, glDrawArrays, glDrawArraysIndirect, glDrawArraysInstanced, glDrawArraysInstancedBaseInstance, glMultiDrawArrays, 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/.