Name
EXT_draw_buffers_indexed
Name Strings
GL_EXT_draw_buffers_indexed
Contact
Daniel Koch, NVIDIA Corporation (dkoch 'at' nvidia.com)
Contributors
Graham Connor, Imagination
Ben Bowman, Imagination
Jonathan Putsman, Imagination
Contributors to EXT_draw_buffers2
Contributors to ARB_draw_buffers_blend
Status
Complete.
Version
Last Modified Date: July 14, 2014
Revision: 5
Number
OpenGL ES Extension #176
Dependencies
OpenGL ES 3.0 or EXT_draw_buffers is required.
This extension is written against the OpenGL ES 3.0 specification.
Overview
This extension builds upon the EXT_draw_buffers extension.
In EXT_draw_buffers (part of OpenGL ES 3.0), separate values could
be written to each color buffer, but the blend enable, blend functions,
blend equations and color write masks are global and apply to all color
outputs.
This extension provides the ability to independently
* enable or disable blending,
* set the blend equations,
* set the blend functions, and
* set the color write masks
per color output.
This extension introduces indexed versions of the enable,
blend equation, blend function, and color mask commands, as
well as associated indexed queries in order to control and
query these states independently on a per-color output basis.
New Procedures and Functions
void EnableiEXT(enum target, uint index);
void DisableiEXT(enum target, uint index);
void BlendEquationiEXT(uint buf, enum mode);
void BlendEquationSeparateiEXT(uint buf, enum modeRGB,
enum modeAlpha);
void BlendFunciEXT(uint buf, enum src, enum dst);
void BlendFuncSeparateiEXT(uint buf, enum srcRGB, enum dstRGB,
enum srcAlpha, enum dstAlpha);
void ColorMaskiEXT(uint buf, boolean r, boolean g,
boolean b, boolean a);
boolean IsEnablediEXT(enum target, uint index);
New Tokens
Accepted by the <target> parameter of GetBooleani_v, GetIntegeri_v, and
GetInteger64i_v:
BLEND_EQUATION_RGB
BLEND_EQUATION_ALPHA
BLEND_SRC_RGB
BLEND_SRC_ALPHA
BLEND_DST_RGB
BLEND_DST_ALPHA
COLOR_WRITEMASK
Accepted by the <target> parameter of EnableiEXT, DisableiEXT, and
IsEnablediEXT:
BLEND
Accepted by the <mode> parameter of BlendEquationiEXT and by the
<modeRGB> and <modeAlpha> parameters of BlendEquationSeparateiEXT:
FUNC_ADD
FUNC_SUBTRACT
FUNC_REVERSE_SUBTRACT
MIN
MAX
Accepted by the <src> and <dst> parameters of BlendFunciEXT and
by the <srcRGB>, <dstRGB>, <srcAlpha>, and <dstAlpha> parameters
of BlendFuncSeparateiEXT:
ZERO
ONE
SRC_COLOR
ONE_MINUS_SRC_COLOR
DST_COLOR
ONE_MINUS_DST_COLOR
SRC_ALPHA
ONE_MINUS_SRC_ALPHA
DST_ALPHA
ONE_MINUS_DST_ALPHA
CONSTANT_COLOR
ONE_MINUS_CONSTANT_COLOR
CONSTANT_ALPHA
ONE_MINUS_CONSTANT_ALPHA
SRC_ALPHA_SATURATE
(Note all of the above tokens are already defined in OpenGL ES 3.0.)
Additions to Chapter 2 of the OpenGL ES 3.0 Specification (OpenGL ES Operation)
None.
Additions to Chapter 3 of the OpenGL ES 3.0 Specification (Rasterization)
None.
Additions to Chapter 4 of the OpenGL ES 3.0 Specification (Per-Fragment
Operations and the Framebuffer)
Modify the fifth paragraph of section 4.1.7 (Blending), p. 179, to
read as follows:
"Blending is enabled or disabled for an individual draw buffer with
the commands:
void EnableiEXT(enum target, uint index);
void DisableiEXT(enum target, uint index);
<target> is the symbolic constant BLEND and <index> is an integer
<i> specifying the draw buffer associated with the symbolic constant
DRAW_BUFFER<i>. Blending can be enabled or
disabled for all draw buffers using Enable or Disable with the
symbolic constant BLEND. If blending is disabled for a particular
draw buffer, proceed to the next operation."
Modify section "Blend Equation" replacing the first paragraph beginning
on p. 179, with the following:
"Blending is controlled by the blend equation. This equation can be
simultaneously set to the same value for all draw buffers using the
commands:
void BlendEquation(enum mode);
void BlendEquationSeparate(enum modeRGB, enum modeAlpha);
or for an individual draw buffer using the indexed commands:
void BlendEquationiEXT(uint buf, enum mode);
void BlendEquationSeparateiEXT(uint buf
enum modeRGB,
enum modeAlpha);
BlendEquationSeparate and BlendEquationSeparateiEXT argument
<modeRGB> determines the RGB blend equation while <modeAlpha>
determines the alpha blend equation. BlendEquation and
BlendEquationiEXT argument <mode> determines both the RGB and alpha
blend equations. <mode>, <modeRGB>, and <modeAlpha> must be one of
FUNC_ADD, FUNC_SUBTRACT, FUNC_REVERSE_SUBTRACT, MIN, MAX.
BlendEquation and BlendEquationSeparate modify the blend equations
for all draw buffers. BlendEquationiEXT and
BlendEquationSeparateiEXT modify the blend equations associated with
an individual draw buffer. The <buf> argument is an integer <i> that
indicates that the blend equations should be modified for
DRAW_BUFFER<i>."
Modify section "Blend Functions" on p. 181, replacing the last sentence
of the first paragraph and the second paragraph with the following:
"Blend functions are simultaneously specified
for all draw buffers using the commands:
void BlendFunc(enum src, enum dst);
void BlendFuncSeparate(enum srcRGB, enum dstRGB,
enum srcAlpha, enum dstAlpha);
or for an individual draw buffer using the indexed commands:
void BlendFunciEXT(uint buf, enum src, enum dst);
void BlendFuncSeparateiEXT(uint buf, enum srcRGB,
enum dstRGB, enum srcAlpha,
enum dstAlpha);
BlendFuncSeparate and BlendFuncSeparateiEXT arguments <srcRGB> and
<dstRGB> determine the source and destination RGB blend functions,
respectively, while <srcAlpha> and <dstAlpha> determine the source
and destination alpha blend functions. BlendFunc and BlendFunciEXT
argument <src> determines both RGB and alpha source functions, while
<dst> determines both RGB and alpha destination functions.
BlendFuncSeparate and BlendFunc modify the blend functions for all
draw buffers. BlendFuncSeparateiEXT and BlendFunciEXT modify the
blend functions associated with an individual draw buffer. The <buf>
argument is an integer <i> that indicates that the blend equations
should be modified for DRAW_BUFFER<i>."
Modify section "Blending State" on p. 183, replacing the first two
paragraphs with the following:
"The state required for blending, for each draw buffer, is two
integers for the RGB and alpha blend equations, four integers
indicating the source and destination RGB and alpha blending
functions, and a bit indicating whether blending is enabled or
disabled. Additionally, four floating-point values to store the RGBA
constant blend color are required.
For all draw buffers, the initial blend equations for RGB and alpha
are both FUNC_ADD, and the initial blending functions are ONE for
the source RGB and alpha functions, and ZERO for the destination RGB
and alpha functions. Initially, blending is disabled for all draw
buffers. The initial constant blend color is (R,G,B,A) = (0,0,0,0).
The value of the blend enable for draw buffer <i> can be queried by
calling IsEnablediEXT with <target> BLEND and <index> <i>, and the
values of the blend equations and functions can be queried by calling
GetIntegeri_v with the corresponding <target> as shown in
table 6.11 and <index> <i>.
The value of the blend enable, or the blend equations and functions
for draw buffer zero may also be queried by calling IsEnabled, or
GetInteger, respectively, with the same symbolic constants but no
<index> parameter."
Modify section 4.2.2 (Fine Control of Buffer Updates) replacing the
first two paragraphs as follows:
"Writing to bits of each of the logical framebuffers after all
per-fragment operations have been performed may be "masked". The
commands:
void ColorMask(boolean r, boolean g, boolean b, boolean a);
void ColorMaskiEXT(uint buf, boolean r, boolean g,
boolean b, boolean a);
control writes to the active draw buffers.
ColorMask and ColorMaskiEXT are used to mask
the writing of R, G, B and A values to the draw buffer or buffers.
ColorMaskiEXT sets the mask for a particular draw buffer.
The mask for DRAW_BUFFER<i> is modified by passing <i> as the parameter
<buf>. <r>, <g>, <b>, and <a> indicate whether R, G, B, or A
values, respectively, are written or not (a value of TRUE means
that the corresponding value is written). The mask specified by
<r>, <g>, <b>, and <a> is applied to the color buffer associated
with DRAW_BUFFER<i>.
ColorMask sets the mask for all draw buffers to the same values as
specified by <r>, <g>, <b>, and <a>.
In the initial state, all color values are enabled for writing for all
draw buffers.
The value of the color writemask for draw buffer <i> can be queried
by calling GetBooleani_v with <target> COLOR_WRITEMASK and <index>
<i>. The value of the color writemask for draw buffer zero may also be
queried by calling GetBooleanv with the symbolic constant COLOR_WRITEMASK."
Additions to Chapter 5 of the OpenGL ES 3.0 Specification (Special Functions)
None.
Additions to Chapter 6 of the OpenGL ES 3.0 Specification (State and
State Requests)
Modify section 6.1.1 (Simple Queries) p. 226.
Replace the 3rd paragraph with the following:
"Finally,
boolean IsEnabled(enum cap);
can be used to determine if <cap> is currently enabled (as with
Enable) or disabled, and
boolean IsEnablediEXT(enum target, uint index);
can be used to determine if the index state corresponding to
<target> and <index> is enabled or disabled.
Additions to Appendix A of the OpenGL ES 3.0 Specification (Invariance)
None.
Additions to the EGL/AGL/GLX/WGL Specifications
None.
Errors
The error INVALID_VALUE is generated by BlendEquationiEXT,
BlendEquationSeparateiEXT, BlendFuncSeparateiEXT, and
BlendFunciEXT if the <buf> parameter is outside the range
[0, MAX_DRAW_BUFFERS-1].
The error INVALID_VALUE is generated by GetIntegeri_v
if <target> is BLEND_EQUATION_RGB, BLEND_EQUATION_ALPHA, BLEND_SRC_RGB,
BLEND_SRC_ALPHA, BLEND_DST_RGB, BLEND_DST_ALPHA, and <index> is outside
the range [0, MAX_DRAW_BUFFERS-1].
The error INVALID_ENUM is generated by BlendFunciEXT
if either <src>, or <dst> is not an accepted value.
The error INVALID_ENUM is generated by BlendFuncSeparateiEXT
if either <srcRGB>, <dstRGB>, <srcAlpha>, or <dstAlpha> is not
an accepted value.
The error INVALID_ENUM is generated if the <mode> parameter of
BlendEquationiEXT is not one of FUNC_ADD, FUNC_SUBTRACT,
FUNC_REVERSE_SUBTRACT, MAX, or MIN.
The error INVALID_ENUM is generated if either the <modeRGB> or
<modeAlpha> parameter of BlendEquationSeparateiEXT is not one of
FUNC_ADD, FUNC_SUBTRACT, FUNC_REVERSE_SUBTRACT, MAX, or MIN.
The error INVALID_ENUM is generated by EnableiEXT and
DisableiEXT if the <target> parameter is not BLEND.
The error INVALID_VALUE is generated by EnableiEXT and
DisableiEXT if the <target> parameter is BLEND and the <index>
parameter is outside the range [0, MAX_DRAW_BUFFERS-1].
The error INVALID_ENUM is generated by IsEnablediEXT if the
<target> parameter is not BLEND.
The error INVALID_VALUE is generated by IsEnablediEXT if
the <target> parameter is BLEND and the <index> parameter is
outside the range [0, MAX_DRAW_BUFFERS-1].
The error INVALID_VALUE is generated by ColorMaskiEXT
if the <buf> parameter is outside the range[0, MAX_DRAW_BUFFERS-1].
The error INVALID_VALUE is generated by GetBooleani_v if the <target>
parameter is COLOR_WRITEMASK and the <index> parameter is outside the
range [0, MAX_DRAW_BUFFERS-1].
New State
Modify Table 6.11 (Pixel Operations) p. 254, modifying the entries for
BLEND enable, the blend functions and blend equations, adding indexed
versions:
Initial
Get Value Type Get Command Value Description Section
-------------------- --------- ------------- -------- ------------------------------------ -------
BLEND B IsEnablediEXT False Blending enabled for draw buffer <i> 4.1.7
where <i> is specified as <index>
BLEND_SRC_RGB 4* x Z_19 GetIntegeri_v ONE Blending source RGB 4.1.7
function for draw buffer <i>
where <i> is specified as <index>
BLEND_SRC_ALPHA 4* x Z_19 GetIntegeri_v ONE Blending source A 4.1.7
function for draw buffer <i>
where <i> is specified as <index>
BLEND_DST_RGB 4* x Z_19 GetIntegeri_v ZERO Blending destination RGB 4.1.7
function for draw buffer <i>
where <i> is specified as <index>
BLEND_DST_ALPHA 4* x Z_19 GetIntegeri_v ZERO Blending destination A 4.1.7
function for draw buffer <i>
where <i> is specified as <index>
BLEND_EQUATION_RGB 4* x Z_5 GetIntegeri_v FUNC_ADD RGB blending equation 4.1.7
for draw buffer <i>
where <i> is specified as <index>
BLEND_EQUATION_ALPHA 4* x Z_5 GetIntegeri_v FUNC_ADD Alpha blending equation 4.1.7
for draw buffer <i>
where <i> is specified as <index>
Modify Table 6.12 (Framebuffer Control) p. 255, modifying the entry for
COLOR_WRITEMASK:
Get Value Type Get Command Value Description Section
--------------- -------- ------------- ------ ---------------------------------- -------
COLOR_WRITEMASK 4* x 4xB GetBooleani_v 4xTrue Color write enables (R, G, B, A) 4.2.2
for draw buffer <i>
where <i> is specified as <index>
Issues
Note: these issues apply specifically to the definition of
EXT_draw_buffers_indexed, which is based on the OpenGL EXT_draw_buffers2
and ARB_draw_buffers_blend extensions as updated in OpenGL 4.x.
Resolved issues from EXT_draw_buffers2 and ARB_draw_buffers_blend have
been removed but remain largely applicable to this extension. These
extensions can be found in the OpenGL Registry.
(1) What functionality was removed from EXT_draw_buffers2 and
ARB_draw_buffers_blend?
- removed mention of multiple buffers being associated with DRAW_BUFFER<i>
- removed mention of logical operation on color values
- removed mention of the IndexMask command
- removed errors related to glBegin/End
(2) What functionality was changed or added relative to EXT_draw_buffers2
and ARB_draw_buffers_blend?
- use EnableiEXT/DisableiEXT instead of Enable/DisableIndexedEXT
- use ColorMaskiEXT instead of ColorMaskIndexedEXT
- use IsEnablediEXT instead of IsEnabledIndexedEXT
- GetIntegeri_v is already in ES 3.0 and is re-used instead of adding
GetIntegerIndexedvEXT.
- GetBooleani_v is already in ES 3.1 and is re-used instead of adding
GetBooleanIndexedvEXT
- change the errors to be consistent and match GL 4.4.
(3) What should we call this extension?
RESOLVED: EXT_draw_buffers_indexed, because it adds the indexed "i"
variants of all the draw buffer related state setting commands.
Other options considered include:
* EXT_draw_buffers2, EXT_draw_buffers_blend: both potentially confusing due
to similarly named GL extensions, while this incorporates the functionality
of both. Furthermore, this will likely be an EXT extension and there already
is an EXT_draw_buffers2 in the GL registry. Using the same name and having
different functionality is strongly discouraged.
* EXT_draw_buffers_separate: because it allows separate control of the drawing
buffers. Potentially could be confused with the "blend_func_separate" and
"blend_equation_separate" extensions, which allow separately controlling a
of the RGB and A equations and functions.
* EXT_draw_buffers_independent: because it allows the functionality of the
separate drawing buffers to be independently controlled.
(4) Why doesn't this extension include GetBooleani_vEXT?
RESOLVED: GetBooleani_v was added in OpenGL ES 3.1 per Bug 11326 and thus
no longer needs to be added by this extension. This extension does
however extend the commands accepted by this core function.
(5) What is the correct error for all the commands which take a <buf>
or <index> parameter which should be in the range [0, MAX_DRAW_BUFFERS-1]?
RESOLVED: INVALID_VALUE is the correct error.
EXT_draw_buffers2 specified INVALID_OPERATION for the EnableIndexedEXT,
DisableIndexedEXT, IsEnabledIndexedEXT, and GetBooleanIndexedvEXT commands.
ARB_draw_buffers_blend specified INVALID_ENUM for the
Blend{Equation Func}[Separate]iARB commands.
OpenGL 4.4 specifies INVALID_VALUE for the core versions of all these
commands. This was clarified by Bug 7705, but never propagated back to
the ARB_draw_buffers_blend extension. Since we are basing the
functionality on the core versions of these commands we will use the
GL 4.x error values.
(6) What is the correct error for the Blend{Equation Func}[Separate]iEXT
commands if mode/modeRGB/modeAlpha/srcRGB/srcAlpha/dstRGB/dstAlpha is
not a legal value?
RESOLVED. INVALID_ENUM. Some versions of the GL 4.4 spec said it should be
INVALID_VALUE, but it seems that the more correct error value should
INVALID_ENUM since all of these values are specified as 'enum' in the
function signatures. This was clarified in Bug 11354.
Revision History
Rev. Date Author Changes
---- -------- -------- -----------------------------------------
5 07/14/14 dkoch Remove stray tokens from error (bug 12358)
4 03/26/14 dkoch Update contributors.
3 03/10/14 Jon Leech Change NNN suffix to EXT.
2 12/16/13 dkoch Removed GetBooleani_vEXT.
Resolved Issues 4 and 6.
Expanded out New Tokens section to clarify the
tokens accepted by the new functions.
1 12/02/13 dkoch Initial revision based on EXT_draw_buffers2 v10
and ARB_draw_buffers_blend v4 and updated with
GL 4.4 commands and language.
