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 Name

     ANGLE_framebuffer_multisample

 Name Strings

     GL_ANGLE_framebuffer_multisample

 Contributors

     Contributors to EXT_framebuffer_multisample

     Daniel Koch, TransGaming Inc.

     Shannon Woods, TransGaming Inc.

     Kenneth Russell, Google Inc.

     Vangelis Kokkevis, Google Inc.

 Contacts

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

 Status

     Implemented in ANGLE ES2

 Version

     Last Modified Date: Aug 6, 2010 

     Author Revision: #3

 Number

     OpenGL ES Extension #84

 Dependencies

     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.

 Overview

     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).

 New Procedures and Functions

     void RenderbufferStorageMultisampleANGLE(

             enum target, sizei samples,

             enum internalformat,

             sizei width, sizei height);

 New Types

     None.

 New Tokens

     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

 Additions to Chapter 2 of the OpenGL ES 2.0 Specification (OpenGL Operation)

 Additions to Chapter 3 of the OpenGL ES 2.0 Specification (Rasterization)

     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."

 Additions to Chapter 4 of the OpenGL ES 2.0 Specification (Per-Fragment

 Operations and the Framebuffer)

     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.

 Additions to Chapter 5 of the OpenGL ES 2.0 Specification (Special Functions)

 Additions to Chapter 6 of the OpenGL ES 2.0 Specification (State and State

 Requests)

     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>."

 Dependencies on ANGLE_framebuffer_blit    

     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.

 Dependencies on OES_texture_3D

     On an OpenGL ES implementation, in the absense of OES_texture_3D,

     omit references to CopyTexSubImage3DOES.

 Errors

     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.

 New State

     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

     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 History

     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