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.

GL_LINE_STRIP_ADJACENCY, GL_LINES_ADJACENCY, GL_TRIANGLE_STRIP_ADJACENCY, GL_TRIANGLES_ADJACENCY and GL_PATCHES are available only if the GL ES version is 3.2 or greater.

Errors

GL_INVALID_ENUM is generated if mode is not an accepted value.

GL_INVALID_OPERATION is generated if zero is bound to the GL_VERTEX_ARRAY_BINDING, GL_DRAW_INDIRECT_BUFFER, or GL_ELEMENT_ARRAY_BUFFER binding, or to any enabled vertex array.

GL_INVALID_OPERATION is generated if the command would source data beyond the end of any bound buffer object.

GL_INVALID_VALUE is generated if indirect is not a multiple of the size, in basic machine units, of GLuint.

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.

API Version Support

See Also

glDrawArrays, glDrawArraysInstanced, glDrawArraysIndirect, glDrawElements, glDrawRangeElements,

Copyright

Copyright © 2010-2019 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. https://opencontent.org/openpub/.