ANGLE_framebuffer_multisample

GL_ANGLE_framebuffer_multisample

Contributors to EXT_framebuffer_multisample
Daniel Koch, TransGaming Inc.
Shannon Woods, TransGaming Inc.
Kenneth Russell, Google Inc.
Vangelis Kokkevis, Google Inc.

Daniel Koch, TransGaming Inc. (daniel 'at' transgaming 'dot' com)

Implemented in ANGLE ES2

Last Modified Date: Aug 6, 2010 
Author Revision: #3

OpenGL ES Extension #84

Requires OpenGL ES 2.0.

Requires GL_ANGLE_framebuffer_blit (or equivalent functionality).

The extension is written against the OpenGL ES 2.0 specification. 

OES_texture_3D affects the definition of this extension.

This extension extends the framebuffer object framework to
enable multisample rendering.

The new operation RenderbufferStorageMultisampleANGLE() allocates
storage for a renderbuffer object that can be used as a multisample
buffer.  A multisample render buffer image differs from a
single-sample render buffer image in that a multisample image has a
number of SAMPLES that is greater than zero.  No method is provided
for creating multisample texture images.

All of the framebuffer-attachable images attached to a framebuffer
object must have the same number of SAMPLES or else the framebuffer
object is not "framebuffer complete".  If a framebuffer object with
multisample attachments is "framebuffer complete", then the
framebuffer object behaves as if SAMPLE_BUFFERS is one.

The resolve operation is affected by calling 
BlitFramebufferANGLE (provided by the ANGLE_framebuffer_blit
extension) where the source is a multisample application-created
framebuffer object and the destination is a single-sample
framebuffer object (either application-created or window-system
provided).

void RenderbufferStorageMultisampleANGLE(
        enum target, sizei samples,
        enum internalformat,
        sizei width, sizei height);

None.

Accepted by the <pname> parameter of GetRenderbufferParameteriv:

    RENDERBUFFER_SAMPLES_ANGLE                  0x8CAB

Returned by CheckFramebufferStatus:

    FRAMEBUFFER_INCOMPLETE_MULTISAMPLE_ANGLE    0x8D56

Accepted by the <pname> parameter of GetBooleanv, GetIntegerv,
and GetFloatv:

    MAX_SAMPLES_ANGLE                           0x8D57

Add to the last paragraph of 3.7.2 (Alternate Texture Image Specification)
(as modified by ANGLE_framebuffer_blit) the following:

"Calling CopyTexSubImage3DOES, CopyTexImage2D or CopyTexSubImage2D will
result in INVALID_OPERATION being generated if the object bound to
READ_FRAMEBUFFER_BINDING_ANGLE is "framebuffer complete" and the value
of SAMPLE_BUFFERS is greater than zero."

Add to 4.3.1 (Reading Pixels), right before the subsection titled
"Obtaining Pixels from the Framebuffer":

"ReadPixels generates INVALID_OPERATION if READ_FRAMEBUFFER_BINDING_ANGLE
(section 4.4) is non-zero, the read framebuffer is framebuffer
complete, and the value of SAMPLE_BUFFERS for the read framebuffer
is greater than zero."

In 4.3.2 (Copying Pixels), add to the section describing BlitFramebuffer
that was added by ANGLE_framebuffer_blit.

"If SAMPLE_BUFFERS for the read framebuffer is greater than zero and
SAMPLE_BUFFERS for the draw framebuffer is zero, the samples
corresponding to each pixel location in the source are converted to
a single sample before being written to the destination.

If SAMPLE_BUFFERS for the draw framebuffer is greater than zero, 
no copy is performed and an INVALID_OPERATION error is generated.

If SAMPLE_BUFFERS for the read framebuffer is greater than zero and
<mask> includes DEPTH_BUFFER_BIT or STENCIL_BUFFER_BIT, no copy is 
performed and an INVALID_OPERATION error is generated.

If SAMPLE_BUFFERS for the read framebuffer is greater than zero and 
the format of the read and draw framebuffers are not identical, no
copy is performed and an INVALID_OPERATION error is generated.

If SAMPLE_BUFFERS for the read framebuffer is greater than zero, the
dimensions of the source and destination rectangles provided to 
BlitFramebufferANGLE must be identical and must specify the complete 
source and destination buffers, otherwise no copy is performed and 
an INVALID_OPERATION error is generated."

Modification to 4.4.3 (Renderbuffer Objects)

Add, just above the definition of RenderbufferStorage:

"The command

    void RenderbufferStorageMultisampleANGLE(
        enum target, sizei samples,
        enum internalformat,
        sizei width, sizei height);

establishes the data storage, format, dimensions, and number of
samples of a renderbuffer object's image.  <target> must be
RENDERBUFFER.  <internalformat> must be one of the color-renderable,
depth-renderable, or stencil-renderable formats described in table 4.5.
<width> and <height> are the dimensions in pixels of the renderbuffer.  If
either <width> or <height> is greater than the value of 
MAX_RENDERBUFFER_SIZE, or if <samples> is greater than MAX_SAMPLES_ANGLE, 
then the error INVALID_VALUE is generated. If OpenGL ES is unable to 
create a data store of the requested size, the error OUT_OF_MEMORY 
is generated.

Upon success, RenderbufferStorageMultisampleANGLE deletes any existing
data store for the renderbuffer image and the contents of the data
store after calling RenderbufferStorageMultisampleANGLE are undefined.
RENDERBUFFER_WIDTH is set to <width>, RENDERBUFFER_HEIGHT is
set to <height>, and RENDERBUFFER_INTERNAL_FORMAT is set to
<internalformat>.

If <samples> is zero, then RENDERBUFFER_SAMPLES_ANGLE is set to zero.
Otherwise <samples> represents a request for a desired minimum
number of samples. Since different implementations may support
different sample counts for multisampled rendering, the actual
number of samples allocated for the renderbuffer image is
implementation dependent.  However, the resulting value for
RENDERBUFFER_SAMPLES_ANGLE is guaranteed to be greater than or equal
to <samples> and no more than the next larger sample count supported
by the implementation.

An OpenGL ES implementation may vary its allocation of internal component
resolution based on any RenderbufferStorageMultisampleANGLE parameter (except
target), but the allocation and chosen internal format must not be a
function of any other state and cannot be changed once they are
established. The actual resolution in bits of each component of the 
allocated image can be queried with GetRenderbufferParameteriv."

Modify the definiton of RenderbufferStorage as follows:

"The command

    void RenderbufferStorage(enum target, enum internalformat,
                                sizei width, sizei height);

 is equivalent to calling RenderbufferStorageMultisampleANGLE with
 <samples> equal to zero."

In section 4.4.5 (Framebuffer Completeness) in the subsection
titled "Framebuffer Completeness" add an entry to the bullet list:

* The value of RENDERBUFFER_SAMPLES_ANGLE is the same for all attached
  images.
  { FRAMEBUFFER_INCOMPLETE_MULTISAMPLE_ANGLE }

Also add a paragraph to the end of the section after the definition
of CheckFramebufferStatus:

"The values of SAMPLE_BUFFERS and SAMPLES are derived from the
attachments of the currently bound framebuffer object.  If the
current DRAW_FRAMEBUFFER_BINDING_ANGLE is not "framebuffer complete",
then both SAMPLE_BUFFERS and SAMPLES are undefined.  Otherwise,
SAMPLES is equal to the value of RENDERBUFFER_SAMPLES_ANGLE for the
attached images (which all must have the same value for
RENDERBUFFER_SAMPLES_ANGLE).  Further, SAMPLE_BUFFERS is one if
SAMPLES is non-zero.  Otherwise, SAMPLE_BUFFERS is zero.

In section 6.1.3 (Enumeraged Queries), modify the third paragraph 
of the description of GetRenderbufferParameteriv as follows:

"Upon successful return from GetRenderbufferParameteriv, if
<pname> is RENDERBUFFER_WIDTH, RENDERBUFFER_HEIGHT,
RENDERBUFFER_INTERNAL_FORMAT, or RENDERBUFFER_SAMPLES_ANGLE, then <params> 
will contain the width in pixels, height in pixels, internal format, or 
number of samples, respectively, of the image of the renderbuffer 
currently bound to <target>."

ANGLE_framebuffer_blit is required.  Technically, ANGLE_framebuffer_blit
would not be required to support multisampled rendering, except for
the fact that it provides the only method of doing a multisample
resovle from a multisample renderbuffer.

On an OpenGL ES implementation, in the absense of OES_texture_3D,
omit references to CopyTexSubImage3DOES.

The error INVALID_OPERATION is generated if ReadPixels or 
CopyTex{Sub}Image* is called while READ_FRAMEBUFFER_BINDING_ANGLE
is non-zero, the read framebuffer is framebuffer complete, and the
value of SAMPLE_BUFFERS for the read framebuffer is greater than
zero.

If both the draw and read framebuffers are framebuffer complete and
the draw framebuffer has a value of SAMPLE_BUFFERS that is greater 
than zero, then the error INVALID_OPERATION is generated if 
BlitFramebufferANGLE is called.

If both the draw and read framebuffers are framebuffer complete and
the read framebuffer has a value of SAMPLE_BUFFERS that is greater
than zero, the error INVALID_OPERATION is generated if 
BlitFramebufferANGLE is called and any of the following conditions
are true:
 - <mask> includes DEPTH_BUFFER_BIT or STENCIL_BUFFER_BIT.
 - the source or destination rectangles do not specify the entire
   source or destination buffer.

If both the draw and read framebuffers are framebuffer complete and
either has a value of SAMPLE_BUFFERS that is greater than zero, then
the error INVALID_OPERATION is generated if BlitFramebufferANGLE is
called and the formats of the draw and read framebuffers are not
identical.

If either the draw or read framebuffer is framebuffer complete and
has a value of SAMPLE_BUFFERS that is greater than zero, then the
error INVALID_OPERATION is generated if BlitFramebufferANGLE is called
and the specified source and destination dimensions are not
identical.

If RenderbufferStorageMultisampleANGLE is called with <target> not
equal to RENDERBUFFER, the error INVALID_ENUM is generated.

If RenderbufferStorageMultisampleANGLE is called with an 
<internalformat> that is not listed as one of the color-, depth- 
or stencil-renderable formats in Table 4.5, then the error
INVALID_ENUM is generated.

If RenderbufferStorageMultisampleANGLE is called with <width> or 
<height> greater than MAX_RENDERBUFFER_SIZE, then the error 
INVALID_VALUE is generated.

If RenderbufferStorageMultisampleANGLE is called with a value of
<samples> that is greater than MAX_SAMPLES_ANGLE or less than zero,
then the error INVALID_VALUE is generated.

The error OUT_OF_MEMORY is generated when
RenderbufferStorageMultisampleANGLE cannot create storage of the
specified size.

Add to table 6.22 (Renderbuffer State)

Get Value                          Type    Get Command                 Initial Value  Description             Section
-------------------------------    ------  --------------------------  -------------  --------------------    -------
RENDERBUFFER_SAMPLES_ANGLE         Z+      GetRenderbufferParameteriv  0              number of samples       4.4.3


Add to table 6.yy (Framebuffer Dependent Vaues) (added by 
ANGLE_framebuffer_blit), the following new framebuffer dependent state.

Get Value          Type  Get Command     Minimum Value    Description             Section
-----------------  ----  -----------     -------------    -------------------     -------
MAX_SAMPLES_ANGLE  Z+    GetIntegerv     1                Maximum number of       4.4.3
                                                          samples supported
                                                          for multisampling

Issues from EXT_framebuffer_multisample have been removed.
 
1) What should we call this extension?

   Resolved: ANGLE_framebuffer_blit.  

   This extension is a result of a collaboration between Google and 
   TransGaming for the open-source ANGLE project. Typically one would
   label a multi-vendor extension as EXT, but EXT_framebuffer_mulitsample 
   is already the name for this on Desktop GL.  Additionally this
   isn't truely a multi-vendor extension because there is only one
   implementation of this.  We'll follow the example of the open-source
   MESA project which uses the project name for the vendor suffix.
 
2) How does this extension differ from EXT_framebuffer_multisample?

   This is designed to be a proper subset of EXT_framebuffer_multisample
   functionality as applicable to OpenGL ES 2.0.

   Functionality that is unchanged: 
    - creation of multisample renderbuffers.
    - whole buffer multi-sample->single-sample resolve.
    - no format conversions, stretching or flipping supported on multisample blits.

   Additional restrictions on BlitFramebufferANGLE:
    - multisample resolve is only supported on color buffers.
    - no blits to multisample destinations (no single->multi or multi-multi).
    - only entire buffers can be resolved.

Revision 1, 2010/07/08
  - copied from revision 7 of EXT_framebuffer_multisample
  - removed language that was not relevant to ES2 
  - rebase changes against the Open GL ES 2.0 specification
  - added ANGLE-specific restrictions
Revision 2, 2010/07/19
  - fix missing error code
Revision 3, 2010/08/06
  - add additional contributors, update implementation status
  - disallow negative samples