Updates to MRT extension.
Trac #21120
01/30/2013 dgkoch add issue 6 and clear interactions
renamed to EXT_draw_buffers based on feedback
changed resolution of issue 3.
git-svn-id: https://angleproject.googlecode.com/svn/branches/dx11proto@1812 736b8ea6-26fd-11df-bfd4-992fa37f6226
diff --git a/extensions/ANGLE_multiple_render_targets.txt b/extensions/ANGLE_multiple_render_targets.txt
index ba551d2..7354602 100644
--- a/extensions/ANGLE_multiple_render_targets.txt
+++ b/extensions/ANGLE_multiple_render_targets.txt
@@ -1,10 +1,10 @@
Name
- ANGLE_multiple_render_targets
+ EXT_draw_buffers
Name Strings
- GL_ANGLE_multiple_render_targets
+ GL_EXT_draw_buffers
Contributors
@@ -17,20 +17,22 @@
Daniel Koch, TransGaming Inc.
Alastair Patrick, Google Inc.
Kenneth Russell, Google Inc.
- Members of the WebGL working group
+ Greg Roth, NVIDIA Corporation
+ Ben Bowman, Imagination Technologies
+ Members of the WebGL and OpenGL ES working groups
Contact
- Daniel Koch <daniel> <at> <transgaming> <dot> <com>
+ Daniel Koch (daniel 'at' transgaming.com)
Status
- Incomplete -- do not implement!
+ Draft Complete
Version
- Last Modified Date: January 23, 2013
- Revision: #6
+ Last Modified Date: January 30, 2013
+ Revision: #7
Number
@@ -58,60 +60,60 @@
New Procedures and Functions
- void DrawBuffersANGLE(sizei n, const enum *bufs);
+ void DrawBuffersEXT(sizei n, const enum *bufs);
New Tokens
Accepted by the <pname> parameter of GetIntegerv:
- MAX_COLOR_ATTACHMENTS_ANGLE 0x8CDF
+ MAX_COLOR_ATTACHMENTS_EXT 0x8CDF
Accepted by the <pname> parameters of GetIntegerv and GetFloatv:
- MAX_DRAW_BUFFERS_ANGLE 0x8824
- DRAW_BUFFER0_ANGLE 0x8825
- DRAW_BUFFER1_ANGLE 0x8826
- DRAW_BUFFER2_ANGLE 0x8827
- DRAW_BUFFER3_ANGLE 0x8828
- DRAW_BUFFER4_ANGLE 0x8829
- DRAW_BUFFER5_ANGLE 0x882A
- DRAW_BUFFER6_ANGLE 0x882B
- DRAW_BUFFER7_ANGLE 0x882C
- DRAW_BUFFER8_ANGLE 0x882D
- DRAW_BUFFER9_ANGLE 0x882E
- DRAW_BUFFER10_ANGLE 0x882F
- DRAW_BUFFER11_ANGLE 0x8830
- DRAW_BUFFER12_ANGLE 0x8831
- DRAW_BUFFER13_ANGLE 0x8832
- DRAW_BUFFER14_ANGLE 0x8833
- DRAW_BUFFER15_ANGLE 0x8834
+ MAX_DRAW_BUFFERS_EXT 0x8824
+ DRAW_BUFFER0_EXT 0x8825
+ DRAW_BUFFER1_EXT 0x8826
+ DRAW_BUFFER2_EXT 0x8827
+ DRAW_BUFFER3_EXT 0x8828
+ DRAW_BUFFER4_EXT 0x8829
+ DRAW_BUFFER5_EXT 0x882A
+ DRAW_BUFFER6_EXT 0x882B
+ DRAW_BUFFER7_EXT 0x882C
+ DRAW_BUFFER8_EXT 0x882D
+ DRAW_BUFFER9_EXT 0x882E
+ DRAW_BUFFER10_EXT 0x882F
+ DRAW_BUFFER11_EXT 0x8830
+ DRAW_BUFFER12_EXT 0x8831
+ DRAW_BUFFER13_EXT 0x8832
+ DRAW_BUFFER14_EXT 0x8833
+ DRAW_BUFFER15_EXT 0x8834
Accepted by the <attachment> parameter of FramebufferRenderbuffer,
FramebufferTexture2D and GetFramebufferAttachmentParameteriv, and by
- the <bufs> parameter of DrawBuffersANGLE:
+ the <bufs> parameter of DrawBuffersEXT:
- COLOR_ATTACHMENT0_ANGLE 0x8CE0
- COLOR_ATTACHMENT1_ANGLE 0x8CE1
- COLOR_ATTACHMENT2_ANGLE 0x8CE2
- COLOR_ATTACHMENT3_ANGLE 0x8CE3
- COLOR_ATTACHMENT4_ANGLE 0x8CE4
- COLOR_ATTACHMENT5_ANGLE 0x8CE5
- COLOR_ATTACHMENT6_ANGLE 0x8CE6
- COLOR_ATTACHMENT7_ANGLE 0x8CE7
- COLOR_ATTACHMENT8_ANGLE 0x8CE8
- COLOR_ATTACHMENT9_ANGLE 0x8CE9
- COLOR_ATTACHMENT10_ANGLE 0x8CEA
- COLOR_ATTACHMENT11_ANGLE 0x8CEB
- COLOR_ATTACHMENT12_ANGLE 0x8CEC
- COLOR_ATTACHMENT13_ANGLE 0x8CED
- COLOR_ATTACHMENT14_ANGLE 0x8CEE
- COLOR_ATTACHMENT15_ANGLE 0x8CEF
+ COLOR_ATTACHMENT0_EXT 0x8CE0
+ COLOR_ATTACHMENT1_EXT 0x8CE1
+ COLOR_ATTACHMENT2_EXT 0x8CE2
+ COLOR_ATTACHMENT3_EXT 0x8CE3
+ COLOR_ATTACHMENT4_EXT 0x8CE4
+ COLOR_ATTACHMENT5_EXT 0x8CE5
+ COLOR_ATTACHMENT6_EXT 0x8CE6
+ COLOR_ATTACHMENT7_EXT 0x8CE7
+ COLOR_ATTACHMENT8_EXT 0x8CE8
+ COLOR_ATTACHMENT9_EXT 0x8CE9
+ COLOR_ATTACHMENT10_EXT 0x8CEA
+ COLOR_ATTACHMENT11_EXT 0x8CEB
+ COLOR_ATTACHMENT12_EXT 0x8CEC
+ COLOR_ATTACHMENT13_EXT 0x8CED
+ COLOR_ATTACHMENT14_EXT 0x8CEE
+ COLOR_ATTACHMENT15_EXT 0x8CEF
- The COLOR_ATTACHMENT0_ANGLE constant is equal to the
+ The COLOR_ATTACHMENT0_EXT constant is equal to the
COLOR_ATTACHMENT0 constant.
- Each COLOR_ATTACHMENT<i>_ANGLE adheres to COLOR_ATTACHMENT<i>_ANGLE
- = COLOR_ATTACHMENT0_ANGLE + <i>.
+ Each COLOR_ATTACHMENT<i>_EXT adheres to COLOR_ATTACHMENT<i>_EXT
+ = COLOR_ATTACHMENT0_EXT + <i>.
Changes to Chapter 3 of the OpenGL ES 2.0 Specification (Rasterization)
@@ -166,18 +168,18 @@
Insert Table 4.3 to Section 4.2.1 (and renumber subsequent tables):
- Symbolic Constant Meaning
- ----------------- ---------------------
- NONE No buffer
+ Symbolic Constant Meaning
+ ----------------- ---------------------
+ NONE No buffer
- COLOR_ATTACHMENT<i>_ANGLE (see caption) Output fragment color to image
- attached at color attachment
- point i
+ COLOR_ATTACHMENT<i>_EXT (see caption) Output fragment color to image
+ attached at color attachment
+ point i
- Table 4.3: Arguments to DrawBuffersANGLE when the context is bound to a
+ Table 4.3: Arguments to DrawBuffersEXT when the context is bound to a
framebuffer object, and the buffers they indicate. <i> in
- COLOR_ATTACHMENT<i>_ANGLE may range from zero to the value of
- MAX_COLOR_ATTACHMENTS_ANGLE minus one.
+ COLOR_ATTACHMENT<i>_EXT may range from zero to the value of
+ MAX_COLOR_ATTACHMENTS_EXT minus one.
Replace Section 4.2.1, "Selecting a Buffer for Writing" with the following:
@@ -185,11 +187,11 @@
single buffered surfaces or into the back buffer for back buffered
surfaces as determined when making the context current. To control
the color buffer into which each of the fragment color values is
- written, DrawBuffersANGLE is used.
+ written, DrawBuffersEXT is used.
The command
- void DrawBuffersANGLE(sizei n, const enum *bufs);
+ void DrawBuffersEXT(sizei n, const enum *bufs);
defines the draw buffers to which all fragment colors are written.
<n> specifies the number of buffers in <bufs>. <bufs> is a pointer
@@ -207,7 +209,7 @@
and the constant must be BACK or NONE. When draw buffer zero is
BACK, color values are written into the sole buffer for single-
buffered contexts, or into the back buffer for double-buffered
- contexts. If DrawBuffersANGLE is supplied with a constant other than
+ contexts. If DrawBuffersEXT is supplied with a constant other than
BACK and NONE, the error INVALID_OPERATION is generated.
If the GL is bound to a draw framebuffer object, then each of the
@@ -219,27 +221,27 @@
The maximum number of draw buffers is implementation-dependent. The
number of draw buffers supported can be queried by calling
- GetIntegerv with the symbolic constant MAX_DRAW_BUFFERS_ANGLE. An
+ GetIntegerv with the symbolic constant MAX_DRAW_BUFFERS_EXT. An
INVALID_VALUE error is generated if <n> is greater than
- MAX_DRAW_BUFFERS_ANGLE.
+ MAX_DRAW_BUFFERS_EXT.
If the GL is bound to a draw framebuffer object, the <i>th buffer listed
- in <bufs> must be COLOR_ATTACHMENT<i>_ANGLE or NONE. Specifying a
- buffer out of order, BACK, or COLOR_ATTACHMENT<m>_ANGLE where <m> is
- greater than or equal to the value of MAX_COLOR_ATTACHMENTS_ANGLE,
+ in <bufs> must be COLOR_ATTACHMENT<i>_EXT or NONE. Specifying a
+ buffer out of order, BACK, or COLOR_ATTACHMENT<m>_EXT where <m> is
+ greater than or equal to the value of MAX_COLOR_ATTACHMENTS_EXT,
will generate the error INVALID_OPERATION.
- If a fragment shader writes to "gl_FragColor", DrawBuffersANGLE
- specifies the draw buffer, if any, into which the color written to
- "gl_FragColor" is written. If a fragment shader writes to
- "gl_FragData", DrawBuffersANGLE specifies a set of draw buffers
+ If a fragment shader writes to "gl_FragColor", DrawBuffersEXT
+ specifies the set of draw buffers into which the color
+ written to "gl_FragColor" is written. If a fragment shader writes to
+ "gl_FragData", DrawBuffersEXT specifies a set of draw buffers
into which each of the multiple output colors defined by these
variables are separately written. If a fragment shader writes to
neither "gl_FragColor" nor "gl_FragData" the values of the
fragment colors following shader execution are undefined, and may
differ for each fragment color.
- Indicating a buffer or buffers using DrawBuffersANGLE causes
+ Indicating a buffer or buffers using DrawBuffersEXT causes
subsequent pixel color value writes to affect the indicated
buffers. If the GL is bound to a draw framebuffer object and a draw
buffer selects an attachment that has no image attached, then that
@@ -254,7 +256,7 @@
fragment color zero is BACK if there is a default framebuffer
associated with the context, otherwise NONE. For framebuffer
objects, in the initial state the draw buffer for fragment color
- zero is COLOR_ATTACHMENT0_ANGLE.
+ zero is COLOR_ATTACHMENT0_EXT.
For both the default framebuffer and framebuffer objects, the
initial state of draw buffers for fragment colors other than zero is
@@ -262,7 +264,30 @@
The value of the draw buffer selected for fragment color <i> can be
queried by calling GetIntegerv with the symbolic constant
- DRAW_BUFFER<i>_ANGLE."
+ DRAW_BUFFER<i>_EXT."
+
+ Modify Section 4.2.3 (Clearing the Buffers) and replace the first
+ two paragraphs with the following:
+
+ "The GL provides a means for setting portions of every pixel in a
+ particular buffer to the same value. The argument to
+
+ void Clear(bitfield buf);
+
+ is the bitwise OR of a number of values indicating which buffers are
+ to be cleared. The values are COLOR_BUFFER_BIT, DEPTH_BUFFER_BIT, and
+ STENCIL_BUFFER_BIT, indicating the buffers currently enabled for color
+ writing, the depth buffer, and the stencil buffer (see below),
+ respectively. The value to which each buffer is cleared depends on
+ the setting of the clear value for that buffer. If the mask is not a
+ bitwise OR of the specified values, then the error INVALID_VALUE is
+ generated.
+
+ void ClearColor(clampf r, clampf, g, clampf b, clampf a);
+
+ sets the clear value for fixed-point color buffers. Each of the
+ specified components is clamped to [0, 1] and converted to fixed-point
+ as described in section 2.1.2 for framebuffer color components."
Replace the second paragraph of Section 4.4.1 (Binding and Managing
Framebuffer Objects) with the following:
@@ -279,14 +304,14 @@
to the unused name. The resulting framebuffer object is a new state
vector. There is a number of color attachment points, plus one each
for the depth and stencil attachment points. The number of color attachment
- points is equal to the value of MAX_COLOR_ATTACHMENTS_ANGLE."
+ points is equal to the value of MAX_COLOR_ATTACHMENTS_EXT."
Replace the third item in the bulleted list in Section 4.4.1 (Binding
and Managing Framebuffer Objects) with the following:
" * The only color buffer bitplanes are the ones defined by the
- framebuffer attachments points named COLOR_ATTACHMENT0_ANGLE through
- COLOR_ATTACHMENT<n>_ANGLE."
+ framebuffer attachments points named COLOR_ATTACHMENT0_EXT through
+ COLOR_ATTACHMENT<n>_EXT."
Modify Section 4.4.3 (Renderbuffer Objects) in the
"Attaching Renderbuffer Images to a Framebuffer" subsection as follows:
@@ -295,12 +320,12 @@
Name of attachment
---------------------------------------
- COLOR_ATTACHMENT<i>_ANGLE (see caption)
+ COLOR_ATTACHMENT<i>_EXT (see caption)
DEPTH_ATTACHMENT
STENCIL_ATTACHMENT
- Table 4.x: Framebuffer attachment points. <i> in COLOR_ATTACHMENT<i>_ANGLE
- may range from zero to the value of MAX_COLOR_ATTACHMENTS_ANGLE minus 1.
+ Table 4.x: Framebuffer attachment points. <i> in COLOR_ATTACHMENT<i>_EXT
+ may range from zero to the value of MAX_COLOR_ATTACHMENTS_EXT minus 1.
Modify the third sentence of the paragraph following the definition of
FramebufferRenderbuffer to be as follows:
@@ -321,7 +346,7 @@
item in the bulleted list in the "Framebuffer Attachment Completeness"
subsection with the following:
- " * If <attachment> is COLOR_ATTACHMENT<i>_ANGLE, then <image> must
+ " * If <attachment> is COLOR_ATTACHMENT<i>_EXT, then <image> must
have a color-renderable internal format."
Changes to Chapter 6 of the OpenGL ES 2.0 Specification (State and
@@ -337,14 +362,14 @@
Add a new section:
- 3.4.1 GL_ANGLE_multiple_render_targets Extension
+ 3.4.1 GL_EXT_draw_buffers Extension
- To use the GL_ANGLE_multiple_render_targets extension in a shader it
+ To use the GL_EXT_draw_buffers extension in a shader it
must be enabled using the #extension directive.
The shading language preprocessor #define
- GL_ANGLE_multiple_render_targets will be defined to 1, if the
- GL_ANGLE_multiple_render_targets extension is supported.
+ GL_EXT_draw_buffers will be defined to 1, if the
+ GL_EXT_draw_buffers extension is supported.
Dependencies on ANGLE_framebuffer_blit and APPLE_framebuffer_multisample:
@@ -364,19 +389,19 @@
Errors
- The INVALID_OPERATION error is generated if DrawBuffersANGLE is called
+ The INVALID_OPERATION error is generated if DrawBuffersEXT is called
when the default framebuffer is bound and any of the following conditions
hold:
- - <n> is greater than 1 and less than MAX_DRAW_BUFFERS_ANGLE,
+ - <n> is greater than 1 and less than MAX_DRAW_BUFFERS_EXT,
- <bufs> contains a value other than BACK or NONE.
- The INVALID_OPERATION error is generated if DrawBuffersANGLE is called
+ The INVALID_OPERATION error is generated if DrawBuffersEXT is called
when bound to a draw framebuffer object and any of the following
conditions hold:
- - the <i>th value in <bufs> is not COLOR_ATTACHMENT<i>_ANGLE or NONE.
+ - the <i>th value in <bufs> is not COLOR_ATTACHMENT<i>_EXT or NONE.
- The INVALID_VALUE error is generated if DrawBuffersANGLE is called
- with a value of <n> which is greater than MAX_DRAW_BUFFERS_ANGLE.
+ The INVALID_VALUE error is generated if DrawBuffersEXT is called
+ with a value of <n> which is greater than MAX_DRAW_BUFFERS_EXT.
The INVALID_ENUM error is generated by FramebufferRenderbuffer if
the <attachment> parameter is not one of the values listed in Table 4.x.
@@ -391,31 +416,36 @@
Add Table 6.X Framebuffer (State per framebuffer object):
- State Type Get Command Initial Value Description
- --------------- ---- ------------ ------------- -----------
- DRAW_BUFFER<i>_ANGLE Z10* GetIntegerv see 4.2.1 Draw buffer selected
+ State Type Get Command Initial Value Description
+ ------------------ ---- ------------ ------------- -----------
+ DRAW_BUFFER<i>_EXT Z10* GetIntegerv see 4.2.1 Draw buffer selected
for fragment color i
Add to Table 6.18 (Implementation Dependent Values)
- Get value Type Get Cmnd Minimum Value Description Sec.
- ------------------------ ---- ----------- ------------- ----------- -----
- MAX_DRAW_BUFFERS_ANGLE Z+ GetIntegerv 1 Maximum number of 4.2.1
- active draw buffers
- MAX_COLOR_ATTACHMENTS_ANGLE Z+ GetIntegerv 1 Number of framebuffer 4.4.1
- color attachment points
+ Get value Type Get Cmnd Minimum Value Description Sec.
+ -------------------- ---- ----------- ------------- ----------- -----
+ MAX_DRAW_BUFFERS_EXT Z+ GetIntegerv 1 Maximum number of 4.2.1
+ active draw buffers
+ MAX_COLOR_ATTACHMENTS_EXT Z+ GetIntegerv 1 Number of framebuffer 4.4.1
+ color attachment points
Issues
See ARB_draw_buffers for relevant issues.
- 1) Differences from NV_draw_buffers + NV_fbo_color_attachments?
+ 1) What are the differences between this extension and NV_draw_buffers
+ + NV_fbo_color_attachments?
- - adds interactions with blit_framebuffer and separate draw/read binding points
- - MAX limits are global instead of per-fbo (see Issue 2)
- - no broadcast from gl_FragColor (see Issue 3)
- - can be used to with default framebuffer to set NONE/BACK (see Issue 4)
+ RESOLVED. This extension:
+ - adds interactions with blit_framebuffer and the separate
+ draw/read binding points
+ - The draw buffer and color attachment limits are global instead
+ of per-fbo (see Issue 2)
+ - can be used to with default framebuffer to set NONE/BACK (see Issue 4)
+ - retains the ordering restrictions on color attachments that are
+ imposed by ES 3.0.
- 2) Should the MAX_DRAW_BUFFERS_ANGLE and MAX_COLOR_ATTACHMENTS_ANGLE limits
+ 2) Should the MAX_DRAW_BUFFERS_EXT and MAX_COLOR_ATTACHMENTS_EXT limits
be per-framebuffer values or implementation dependent constants?
DISCUSSION: In ARB_draw_buffers this was per-context (see Issue 2).
@@ -436,10 +466,10 @@
single-sampled attachments are present.
RESOLVED. Make this global context state as this is most consistent
- with GLES 3.0 and updated GL drivers. Unfortunately this means that a
- D3D9-based implementation of this extension is not possible since D3D9
- does not support multisampled MRTs. Perhaps such an implementation could
- report FBO incomplete in this situation, but that seems less than desirable.
+ with GLES 3.0 and updated GL drivers. In an implementation cannot
+ support multisampling in conjunction with multiple color attachments,
+ perhaps such an implementation could report FBO incomplete in this
+ situation, but this is less than desirable.
3) Should we support broadcast from gl_FragColor to all gl_FragData[x]
or should it be synonymous with gl_FragData[0]?
@@ -454,10 +484,18 @@
writes to gl_FragColor with replicated writes to all possible gl_FragData
locations when this extension is enabled.
- RESOLVED: Broadcast from gl_FragColor to all enabledMRT buffers is not
- supported. A shader author must write gl_FragData[x] if they want to use MRT
-
- 4) Should we allow DrawBuffersANGLE to be called when the default FBO is bound?
+ RESOLVED: Writes to gl_FragColor are broadcast to all enabled color
+ buffers. ES 3.0 using ESSL 1.0 doesn't support broadcast because
+ ESSL 1.0 was not extended to have multiple color outputs (but that is
+ what this extension adds). ESSL 3.0 doesn't support the broadcast because
+ it doesn't have the gl_FragColor variable at all, and only has user-
+ defined out variables. This extension extends ESSL 1.0 to have multiple
+ color outputs. Broadcasting from gl_FragColor to all enabled color
+ buffers is the most consistent with existing draw buffer extensions to
+ date (both NV_draw_buffers and desktop GL).
+
+ 4) Should we allow DrawBuffersEXT to be called when the default FBO is
+ bound?
DISCUSSION: NV_draw_buffers specifies that DrawBuffersNV errors with
INVALID_OPERATION when the default FBO is bound. OpenGL ES 3.0 allows
@@ -466,7 +504,7 @@
An implementation that does not natively support disabling the drawbuffer
on the default FBO could emulate this by disabling color writes.
- RESOLVED: Allow DrawBuffersANGLE to be called for the default FBO. This
+ RESOLVED: Allow DrawBuffersEXT to be called for the default FBO. This
is more forward looking and is compatible with ES 3.0.
5) What are the requirements on the color attachment sizes and formats?
@@ -478,8 +516,17 @@
This extension does not lift those requirements, and failing to meet
them will result in an incomplete FBO.
+ 6) Does this have any interactions with glClear?
+
+ RESOLVED: Yes. When multiple color buffers are enabled for writing,
+ glClear clears all of the color buffers. Added language clarifying
+ that glClear and glClearColor may affect multiple color buffers.
+
Revision History
+ 01/30/2013 dgkoch add issue 6 and clear interactions
+ renamed to EXT_draw_buffers based on feedback
+ changed resolution of issue 3.
01/23/2013 dgkoch add resolutions to issues 2-4.
add issue 5.
Add Table 4.x and update various explicit
