Signature
Parameters
| Variables | Description |
|---|---|
| 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 the address of a structure containing an array of draw parameters.
|
| drawcount |
Specifies the number of elements in the array addressed by
indirect
.
|
| stride |
Specifies the distance in basic machine units between elements of the draw parameter array.
|
Description
glMultiDrawElementsIndirect
specifies multiple indexed geometric primitives
with very few subroutine calls.
glMultiDrawElementsIndirect
behaves
similarly to a multitude of calls to
glDrawElementsInstancedBaseVertexBaseInstance
,
execpt that the parameters to
glDrawElementsInstancedBaseVertexBaseInstance
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 a structure
that takes the form (in C):
typedef struct {
uint count;
uint instanceCount;
uint firstIndex;
uint baseVertex;
uint baseInstance;
} DrawElementsIndirectCommand;
A single call to
glMultiDrawElementsIndirect
is equivalent, assuming no errors
are generated to:
GLsizei n;
for (n = 0; n < drawcount; n++) {
const DrawElementsIndirectCommand *cmd;
if (stride != 0) {
cmd = (const DrawElementsIndirectCommand *)((uintptr)indirect + n * stride);
} else {
cmd = (const DrawElementsIndirectCommand *)indirect + n;
}
glDrawElementsInstancedBaseVertexBaseInstance(mode,
cmd->count,
type,
cmd->firstIndex * size-of-type,
cmd->instanceCount,
cmd->baseVertex,
cmd->baseInstance);
}
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
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_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 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 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.
Version Support
| glMultiDrawElementsIndirect |
See Also
Copyright
Copyright
2010-2014 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/
.