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GL_ATI_draw_buffers
ATI_draw_buffers
Name Strings
GL_ATI_draw_buffers
Contributors
Benj Lipchak
Contact
Rob Mace, ATI Research (mace 'at' ati.com)
Status
Complete.
Version
Last Modified Date: December 30, 2002
Revision: 8
Number
277
Dependencies
The extension is written against the OpenGL 1.3 Specification.
OpenGL 1.3 is required.
ARB_fragment_program affects the definition of this extension.
Overview
This extension extends ARB_fragment_program to allow multiple output
colors, and provides a mechanism for directing those outputs to
multiple color buffers.
Issues
(1) How many GL_DRAW_BUFFER#_ATI enums should be reserved?
RESOLVED: We only need 4 currently, but for future expandability
it would be nice to keep the enums in sequence. We'll specify
16 for now, which will be more than enough for a long time.
void DrawBuffersATI(sizei n, const enum *bufs);
Accepted by the <pname> parameters of GetIntegerv, GetFloatv,
and GetDoublev:
MAX_DRAW_BUFFERS_ATI 0x8824
DRAW_BUFFER0_ATI 0x8825
DRAW_BUFFER1_ATI 0x8826
DRAW_BUFFER2_ATI 0x8827
DRAW_BUFFER3_ATI 0x8828
DRAW_BUFFER4_ATI 0x8829
DRAW_BUFFER5_ATI 0x882A
DRAW_BUFFER6_ATI 0x882B
DRAW_BUFFER7_ATI 0x882C
DRAW_BUFFER8_ATI 0x882D
DRAW_BUFFER9_ATI 0x882E
DRAW_BUFFER10_ATI 0x882F
DRAW_BUFFER11_ATI 0x8830
DRAW_BUFFER12_ATI 0x8831
DRAW_BUFFER13_ATI 0x8832
DRAW_BUFFER14_ATI 0x8833
DRAW_BUFFER15_ATI 0x8834
Additions to Chapter 2 of the OpenGL 1.3 Specification (OpenGL
Operation)
None
Additions to Chapter 3 of the OpenGL 1.3 Specification (Rasterization)
Modify Section 3.11.2, Fragment Program Grammar and Semantic
Restrictions
(replace <resultBinding> grammar rule with these rules)
<resultBinding> ::= "result" "." "color" <optOutputColorNum>
| "result" "." "depth"
<optOutputColorNum> ::= ""
| "[" <outputColorNum> "]"
<outputColorNum> ::= <integer> from 0 to MAX_DRAW_BUFFERS_ATI-1
Modify Section 3.11.3.4, Fragment Program Results
(modify Table X.3)
Binding Components Description
----------------------------- ---------- ----------------------------
result.color[n] (r,g,b,a) color n
result.depth (*,*,*,d) depth coordinate
Table X.3: Fragment Result Variable Bindings. Components labeled
"*" are unused. "[n]" is optional -- color <n> is used if
specified; color 0 is used otherwise.
(modify third paragraph) If a result variable binding matches
"result.color[n]", updates to the "x", "y", "z", and "w" components
of the result variable modify the "r", "g", "b", and "a" components,
respectively, of the fragment's corresponding output color. If
"result.color[n]" is not both bound by the fragment program and
written by some instruction of the program, the output color <n> of
the fragment program is undefined.
Add a new Section 3.11.4.5.3
3.11.4.5.3 Draw Buffers Program Option
If a fragment program specifies the "ATI_draw_buffers" option,
it will generate multiple output colors, and the result binding
"result.color[n]" is allowed, as described in section 3.11.3.4,
and with modified grammar rules as set forth in section 3.11.2.
If this option is not specified, a fragment program that attempts
to bind "result.color[n]" will fail to load, and only "result.color"
will be allowed.
Additions to Chapter 4 of the OpenGL 1.3 Specification (Per-Fragment
Operations and the Frame Buffer)
Modify Section 4.2.1, Selecting a Buffer for Writing (p. 168)
(modify the title and first paragraph, p. 168)
4.2.1 Selecting Color Buffers for Writing
The first such operation is controlling the color buffers into
which each of the output colors are written. This is accomplished
with either DrawBuffer or DrawBuffersATI. DrawBuffer defines the
set of color buffers to which output color 0 is written.
(insert paragraph between first and second paragraph, p. 168)
DrawBuffer will set the draw buffer for output colors other than 0
to NONE. DrawBuffersATI defines the draw buffers to which all
output colors are written.
void DrawBuffersATI(sizei n, const enum *bufs);
<n> specifies the number of buffers in <bufs>. <bufs> is a pointer
to an array of symbolic constants specifying the buffer to which
each output color is written. The constants may be NONE,
FRONT_LEFT, FRONT_RIGHT, BACK_LEFT, BACK_RIGHT, and AUX0 through
AUXn, where n + 1 is the number of available auxiliary buffers. The
draw buffers being defined correspond in order to the respective
output colors. The draw buffer for output colors beyond <n> is set
to NONE.
If the "ATI_draw_buffers" fragment program option, is not being used
then DrawBuffersATI specifies a set of draw buffers into which output
color 0 is written.
The maximum number of draw buffers is implementation dependent and
must be at least 1. The number of draw buffers supported can
be queried with the state MAX_DRAW_BUFFERS_ATI.
The constants FRONT, BACK, LEFT, RIGHT, and FRONT_AND_BACK that
refer to multiple buffers are not valid for use in DrawBuffersATI
and will result in the error INVALID_OPERATION.
If DrawBuffersATI is supplied with a constant (other than NONE)
that does not indicate any of the color buffers allocated to
the GL context, the error INVALID_OPERATION will be generated. If
<n> is greater than MAX_DRAW_BUFFERS_ATI, the error
INVALID_OPERATION will be generated.
(replace last paragraph, p. 169)
The state required to handle color
buffer selection is an integer for each supported output color. In
the initial state, draw buffer for output color 0 is FRONT if there
are no back buffers; otherwise it is BACK. The initial state of
draw buffers for output colors other then 0 is NONE.
Additions to Chapter 5 of the OpenGL 1.3 Specification (Special
Functions)
None
Additions to Chapter 6 of the OpenGL 1.3 Specification (State and
State Requests)
None
Dependencies on ARB_fragment_program
If ARB_fragment_program is not supported then all changes to
section 3.11 are removed.
Interactions with possible future extensions
If there is some other future extension that defines multiple
color outputs then this extension and glDrawBuffersATI could be
used to define the destinations for those outputs. This extension
need not be used only with ARB_fragment_program.
Errors
The error INVALID_OPERATION is generated by DrawBuffersATI if a
color buffer not currently allocated to the GL context is specified.
The error INVALID_OPERATION is generated by DrawBuffersATI if <n>
is greater than the state MAX_DRAW_BUFFERS_ATI.
The error INVALID_OPERATION is generated by DrawBuffersATI if value in
<bufs> does not correspond to one of the allowed buffers.
New State
(table 6.19, p227) add the following entry:
Get Value Type Get Command Initial Value Description Section Attribute
------------------------------- ------ ------------- ------------- -------------------- ------------ ------------
DRAW_BUFFERi_ATI Z10* GetIntegerv see 4.2.1 Draw buffer selected 4.2.1 color-buffer
for output color i
New Implementation Dependent State
Get Value Type Get Command Minimum Value Description Sec. Attribute
--------- ---- ----------- ------------- ------------------- ----- ---------
MAX_DRAW_BUFFERS_ATI Z+ GetIntegerv 1 Maximum number of 4.2.1 -
active draw buffers
Revision History
Date: 12/30/2002
Revision: 8
- Clarified that DrawBuffersATI will set the set of draw buffers to
write color output 0 to when the "ATI_draw_buffer" fragments
program option is not in use.
Date: 9/27/2002
Revision: 7
- Fixed confusion between meaning of color buffer and draw buffer
in last revision.
- Fixed mistake in when an error is generated based on the <n>
argument of DrawBuffersATI.
Date: 9/26/2002
Revision: 6
- Cleaned up and put in sync with latest ARB_fragment_program
revision (#22). Some meaningless changes made just in the name
of consistency.
Date: 9/11/2002
Revision: 5
- Added section 3.11.4.5.3.
- Added enum numbers to New Tokens.
Date: 9/9/2002
Revision: 4
- Changed error from MAX_OUTPUT_COLORS to MAX_DRAW_BUFFERS_ATI.
- Changed 3.10 section numbers to 3.11 to match change to
ARB_fragment_program spec.
- Changed ARB_fragment_program from required to affects, and
added section on interactions with it and future extensions
that define multiple color outputs.
Date: 9/6/2002
Revision: 3
- Changed error to INVALID OPERATION.
- Cleaned up typos.
Date: 8/19/2002
Revision: 2
- Added a paragraph that specifically points out that the
constants that refer to multiple buffers are not allowed with
DrawBuffersATI.
- Changed bufs to <bufs> in a couple of places.
Date: 8/16/2002
Revision: 1
- First draft for circulation.
Implementation Support
List of OpenGL implementations supporting the GL_ATI_draw_buffers extension
Original File
Original text file for the GL_ATI_draw_buffers extension
Page generated on Sun Nov 20 18:40:34 2005