GLAPI/glDrawElementsIndirect

glDrawElementsIndirect

Core in version		4.6
Core since version		4.0
Core ARB extension	ARB_draw_indirect

glDrawElementsIndirect: render indexed primitives from array data, taking parameters from memory

Function Definition

 void glDrawElementsIndirect(GLenum mode​, GLenum type​, const void *indirect​);

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 a byte offset (cast to a pointer type) into the buffer bound to GL_DRAW_INDIRECT_BUFFER, which designates the starting point of the structure containing the draw parameters.

Description

glDrawElementsIndirect specifies multiple indexed geometric primitives with very few subroutine calls. glDrawElementsIndirect behaves similarly to glDrawElementsInstancedBaseVertexBaseInstance, execpt that the parameters to glDrawElementsInstancedBaseVertexBaseInstance are stored in the buffer bound to GL_DRAW_INDIRECT_BUFFER, offset by indirect​ bytes.

The parameters referenced 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;

glDrawElementsIndirect is equivalent to:

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

indirect​ is interpreted as an offset, in basic machine units, into the buffer bound to GL_DRAW_INDIRECT_BUFFER at the time of the call. That buffer and the parameter data stored there is read from the buffer and executed. If no buffer is bound to the GL_ELEMENT_ARRAY_BUFFER binding, an error will be generated.

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_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 buffer object zero is bound to GL_DRAW_INDIRECT_BUFFER binding and the buffer object'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

glBindVertexArray, glDrawArraysIndirect, glDrawElements, glDrawElementsBaseVertex, glDrawElementsInstanced, glDrawElementsInstancedBaseInstance, glDrawElementsInstancedBaseVertex, glDrawElementsInstancedBaseVertexBaseInstance, glDrawRangeElements, glDrawRangeElementsBaseVertex, glMultiDrawElements, glMultiDrawElementsBaseVertex, glMultiDrawElementsIndirect

Copyright

Copyright © 2010 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/.