GLAPI/glDrawElementsIndirect: Difference between revisions

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== Function Definition ==
== Function Definition ==


   void '''glDrawElementsIndirect'''(GLenum ''mode'', GLenum ''type'', const void *''indirect'');
   void '''glDrawElementsIndirect'''(GLenum {{param|mode}}, GLenum {{param|type}}, const void *{{param|indirect}});


; mode
; mode
: Specifies what kind of primitives to render. Symbolic constants {{code|GL_POINTS}}, {{code|GL_LINE_STRIP}}, {{code|GL_LINE_LOOP}}, {{code|GL_LINES}}, {{code|GL_LINE_STRIP_ADJACENCY}}, {{code|GL_LINES_ADJACENCY}}, {{code|GL_TRIANGLE_STRIP}}, {{code|GL_TRIANGLE_FAN}}, {{code|GL_TRIANGLES}}, {{code|GL_TRIANGLE_STRIP_ADJACENCY}}, {{code|GL_TRIANGLES_ADJACENCY}}, and {{code|GL_PATCHES}} are accepted.
: Specifies what kind of primitives to render. Symbolic constants {{enum|GL_POINTS}}, {{enum|GL_LINE_STRIP}}, {{enum|GL_LINE_LOOP}}, {{enum|GL_LINES}}, {{enum|GL_LINE_STRIP_ADJACENCY}}, {{enum|GL_LINES_ADJACENCY}}, {{enum|GL_TRIANGLE_STRIP}}, {{enum|GL_TRIANGLE_FAN}}, {{enum|GL_TRIANGLES}}, {{enum|GL_TRIANGLE_STRIP_ADJACENCY}}, {{enum|GL_TRIANGLES_ADJACENCY}}, and {{enum|GL_PATCHES}} are accepted.
; type
; type
: Specifies the type of data in the buffer bound to the {{code|GL_ELEMENT_ARRAY_BUFFER}} binding.
: Specifies the type of data in the buffer bound to the {{enum|GL_ELEMENT_ARRAY_BUFFER}} binding.
; indirect
; indirect
: Specifies the address of a structure containing the draw parameters.
: Specifies a byte offset (cast to a pointer type) into the buffer bound to {{enum|GL_DRAW_INDIRECT_BUFFER}}, which designates the starting point of the structure containing the draw parameters.


== Description ==
== Description ==


'''glDrawElementsIndirect''' specifies multiple indexed geometric primitives with very few subroutine calls. '''glDrawElementsIndirect''' behaves similarly to [[GLAPI/glDrawElementsInstancedBaseVertexBaseInstance|glDrawElementsInstancedBaseVertexBaseInstance]], execpt that the parameters to [[GLAPI/glDrawElementsInstancedBaseVertexBaseInstance|glDrawElementsInstancedBaseVertexBaseInstance]] are stored in memory at the address given by ''indirect''.
'''glDrawElementsIndirect''' specifies multiple indexed geometric primitives with very few subroutine calls. '''glDrawElementsIndirect''' behaves similarly to {{apifunc|glDrawElementsInstancedBaseVertexBaseInstance}}, execpt that the parameters to {{apifunc|glDrawElementsInstancedBaseVertexBaseInstance}} are stored in the buffer bound to {{enum|GL_DRAW_INDIRECT_BUFFER}}, offset by {{param|indirect}} bytes.


The parameters addressed by ''indirect'' are packed into a structure that takes the form (in C):  
The parameters referenced by {{param|indirect}} are packed into a structure that takes the form (in C):  


<source lang="cpp">
<source lang="cpp">
     typedef  struct {
     typedef  struct {
         uint  count;
         uint  count;
         uint  primCount;
         uint  instanceCount;
         uint  firstIndex;
         uint  firstIndex;
         uint  baseVertex;
         uint  baseVertex;
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     } DrawElementsIndirectCommand;
     } DrawElementsIndirectCommand;
</source>
</source>
'''glDrawElementsIndirect''' is equivalent to:
'''glDrawElementsIndirect''' is equivalent to:


<source lang="cpp">
<source lang="cpp">
Line 44: Line 43:
                                                       cmd->count,
                                                       cmd->count,
                                                       type,
                                                       type,
                                                       cmd->firstIndex + size-of-type,
                                                       cmd->firstIndex * size-of-type,
                                                       cmd->primCount,
                                                       cmd->instanceCount,
                                                       cmd->baseVertex,
                                                       cmd->baseVertex,
                                                       cmd->baseInstance);
                                                       cmd->baseInstance);
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</source>
</source>


If a buffer is bound to the {{code|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.
{{param|indirect}} is interpreted as an offset, in basic machine units, into the buffer bound to {{enum|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 {{enum|GL_ELEMENT_ARRAY_BUFFER}} binding, an error will be generated.
 
Note that indices stored in client memory are not supported. If no buffer is bound to the {{code|GL_ELEMENT_ARRAY_BUFFER}} binding, an error will be generated.
 
The results of the operation are undefined if the {{code|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.
Vertex attributes that are modified by '''glDrawElementsIndirect''' have an unspecified value after '''glDrawElementsIndirect''' returns. Attributes that aren't modified remain well defined.
Line 61: Line 56:
== Notes ==
== 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.
The {{param|baseInstance}} member of the {{param|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 ==
== Errors ==


{{code|GL_INVALID_ENUM}} is generated if ''mode'' is not an accepted value.
{{enum|GL_INVALID_ENUM}} is generated if {{param|mode}} is not an accepted value.
 
{{enum|GL_INVALID_OPERATION}} is generated if no buffer is bound to the {{enum|GL_ELEMENT_ARRAY_BUFFER}} binding, or if such a buffer's data store is currently mapped.


{{code|GL_INVALID_OPERATION}} is generated if no buffer is bound to the {{code|GL_ELEMENT_ARRAY_BUFFER}} binding, or if such a buffer's data store is currently mapped.
{{enum|GL_INVALID_OPERATION}} is generated if buffer object zero is bound to {{enum|GL_DRAW_INDIRECT_BUFFER}} binding and the buffer object's data store is currently mapped.


{{code|GL_INVALID_OPERATION}} is generated if a non-zero buffer object name is bound to an enabled array or to the {{code|GL_DRAW_INDIRECT_BUFFER}} binding and the buffer object's data store is currently mapped.
{{enum|GL_INVALID_OPERATION}} is generated if a non-zero buffer object name is bound to an enabled array or to the {{enum|GL_DRAW_INDIRECT_BUFFER}} binding and the buffer object's data store is currently mapped.


{{code|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.
{{enum|GL_INVALID_OPERATION}} is generated if a geometry shader is active and {{param|mode}} is incompatible with the input primitive type of the geometry shader in the currently installed program object.


{{code|GL_INVALID_OPERATION}} is generated if ''mode'' is {{code|GL_PATCHES}} and no tessellation control shader is active.
{{enum|GL_INVALID_OPERATION}} is generated if {{param|mode}} is {{enum|GL_PATCHES}} and no tessellation control shader is active.


== See Also ==
== See Also ==


[[GLAPI/glDrawArrays|glDrawArrays]], [[GLAPI/glDrawArraysInstanced|glDrawArraysInstanced]], [[GLAPI/glDrawArraysIndirect|glDrawArraysIndirect]], [[GLAPI/glDrawElements|glDrawElements]], [[GLAPI/glDrawRangeElements|glDrawRangeElements]],
{{apifunc|glBindVertexArray}}, {{apifunc|glDrawArraysIndirect}}, {{apifunc|glDrawElements}}, {{apifunc|glDrawElementsBaseVertex}}, {{apifunc|glDrawElementsInstanced}}, {{apifunc|glDrawElementsInstancedBaseInstance}}, {{apifunc|glDrawElementsInstancedBaseVertex}}, {{apifunc|glDrawElementsInstancedBaseVertexBaseInstance}}, {{apifunc|glDrawRangeElements}}, {{apifunc|glDrawRangeElementsBaseVertex}}, {{apifunc|glMultiDrawElements}}, {{apifunc|glMultiDrawElementsBaseVertex}}, {{apifunc|glMultiDrawElementsIndirect}}


== Copyright ==
== Copyright ==

Latest revision as of 15:54, 8 May 2020

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/.

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