glDrawArraysIndirect

glDrawArraysIndirect: man4/glDrawArraysIndirect.xml

glDrawArraysIndirect specifies multiple geometric primitives with very few subroutine calls. glDrawArraysIndirect behaves similarly to glDrawArraysInstancedBaseInstance, execept that the parameters to glDrawArraysInstancedBaseInstance are stored in memory at the address given by indirect. The parameters addressed by indirect are packed into a structure that takes the form (in C):

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

const DrawArraysIndirectCommand *cmd = (const DrawArraysIndirectCommand *)indirect;
glDrawArraysInstancedBaseInstance(mode, cmd->first, cmd->count, cmd->primCount, cmd->baseInstance);

If a buffer is bound to the GL_DRAW_INDIRECT_BUFFER binding at the time of a call to glDrawArraysIndirect, 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 glDrawArraysIndirect have an unspecified value after glDrawArraysIndirect returns. Attributes that aren't modified remain well defined.

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.