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angle/extensions/ANGLE_multiview.txt

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Name
ANGLE_multiview
Name Strings
GL_ANGLE_multiview
Contributors
Martin Radev, NVIDIA Corporation
Olli Etuaho, NVIDIA Corporation
Corentin Wallez, Google
Geoff Lang, Google
Jamie Madill, Google
Contact
Olli Etuaho (oetuaho 'at' nvidia.com)
Status
Incomplete
Version
Last Modified Date: December 8, 2018
Author Revision: 1
Number
OpenGL ES Extension XX
Dependencies
OpenGL ES 3.0 is required.
Overview
Multi-view rendering, achieved through the functionality exposed by
ANGLE, expects the user to issue for each view almost the same
drawing commands and state changes sequentially. This rendering
method scales with the number of views and can be detrimental for
performance in scenes with many draw calls.
This extension addresses the issue by adding means for multi-view
side-by-side rendering onto a single 2D texture and layered
rendering onto the many layers of a 2D texture array. The new vertex
and fragment shader built-in - ViewID_OVR - is added which signifies
the view for which the current vertex or fragment is being
processed, so that per-view transformations can be applied.
IP Status
No known IP claims.
New Tokens
Accepted by the <pname> parameter of GetFramebufferAttachmentParameteriv:
FRAMEBUFFER_ATTACHMENT_TEXTURE_NUM_VIEWS_ANGLE 0x9630
FRAMEBUFFER_ATTACHMENT_TEXTURE_VIEWPORT_OFFSETS_ANGLE 0x969B
FRAMEBUFFER_ATTACHMENT_TEXTURE_BASE_VIEW_INDEX_ANGLE 0x9632
FRAMEBUFFER_ATTACHMENT_TEXTURE_MULTIVIEW_LAYOUT_ANGLE 0x969C
Returned in <params> by GetFramebufferAttachmentParameteriv:
FRAMEBUFFER_MULTIVIEW_SIDE_BY_SIDE_ANGLE 0x969D
FRAMEBUFFER_MULTIVIEW_LAYERED_ANGLE 0x969E
Accepted by the <pname> parameter of GetIntegerv:
MAX_VIEWS_ANGLE 0x9631
Returned by CheckFramebufferStatus:
FRAMEBUFFER_INCOMPLETE_VIEW_TARGETS_ANGLE 0x9633
New Procedures and Functions
void FramebufferTextureMultiviewLayeredANGLE(enum target,
enum attachment,
uint texture,
int level,
int baseViewIndex,
sizei numViews);
void FramebufferTextureMultiviewSideBySideANGLE(enum target,
enum attachment,
uint texture,
int level,
sizei numViews,
const int *viewportOffsets);
Additions to Chapter 2 of the OpenGL ES 3.0 Specification (OpenGL ES Operation)
Modify section 2.9.3 Drawing commands, p. 28
Append to the end of the section:
"
If any drawing command is called the number of views specified in the
program must match the number of views in the draw framebuffer. If
there is a mismatch, an INVALID_OPERATION error is generated.
If the active draw framebuffer has a side-by-side multi-view layout
and the scissor test is not enabled, the result of any draw command
is undefined, but is not followed by program termination.
"
Modify section 2.15.2 Transform Feedback Primitive Capture, p. 91
In the list just after "The error INVALID_OPERATION is generated:"
do the following:
- Add another bullet point:
"
* by any Draw* command if the number of views in the draw
framebuffer is greater than 1 and there is an active and not
paused transform feedback object.
"
Additions to Chapter 3 of the OpenGL ES 3.0 Specification (Rasterization)
Modify section 3.8.5 (Alternate Texture Image Specification Commands),
p. 145
Add at the end of the section:
"Calling CopyTexSubImage3D, CopyTexImage2D, or CopyTexSubImage2D will
result in an INVALID_FRAMEBUFFER_OPERATION error if the multi-view
layout of the current read framebuffer is
FRAMEBUFFER_MULTIVIEW_SIDE_BY_SIDE_ANGLE or the number of views in the
current read framebuffer is more than one."
Additions to Chapter 4 of the OpenGL ES 3.0 Specification
(Per-Fragment Operations and the Framebuffer)
Modify section 4.1.6 (Occlusion queries), p. 177
Replace the first sentence with:
"Occlusion queries use query objects to track whether any fragments
or samples pass the depth test for any of the views."
Append to the sentence
"While that occlusion query is active, the samples-boolean state is
set to TRUE if any fragment or sample passes the depth test"
the text
" for any of the views."
Modify section 4.2.3 (Clearing the Buffers), p. 190
Add a new subsection at the end:
"4.2.3.2 Clearing Multi-view Buffers
Clearing commands are applied to each view in the current multi-view
framebuffer object and have the same constraints as described
in section 4.2.3 Clearing the Buffers.
If the active draw framebuffer has a side-by-side multi-view layout
and the scissor test is not enabled, the clearing command clears
the whole content of the specified buffers.
"
Modify section 4.3.2 (Reading pixels), p. 193
Add to the end of the section:
" ReadPixels generates an INVALID_FRAMEBUFFER_OPERATION error if
the multi-view layout of the current read framebuffer is
FRAMEBUFFER_MULTIVIEW_SIDE_BY_SIDE_ANGLE or the number of views in the
current read framebuffer is more than one."
Modify section 4.3.3 (Copying pixels), p. 198
After the paragraph
"Calling BlitFramebuffer will result in an INVALID_OPERATION error
if filter is LINEAR and read buffer contains integer data."
add a new paragraph:
"Calling BlitFramebuffer will result in an INVALID_FRAMEBUFFER_OPERATION
error if the multi-view layout of the current draw framebuffer is not NONE,
or the multi-view layout of the current read framebuffer is
FRAMEBUFFER_MULTIVIEW_SIDE_BY_SIDE_ANGLE, or the number of views in the
current read framebuffer is more than one."
Modify section 4.4.2 (Attaching Images to Framebuffer Objects), p. 202
Add the following bullet point:
"* Layers of a two-dimensional array texture which can be used for
multi-view rendering."
Modify section 4.4.2.4 (Attaching Texture Images to a Framebuffer), p. 207
Add just before the sentence "Effects of Attaching a Texture Image":
"
The command
SelectView( id );
does not exist in the GL, but it is used to describe the multi-view
functionality in the rest of this section. The effect of this function
is to select the view specified by <id> and set the value to the vertex
and fragment shader built-in gl_ViewID_OVR.
The command
void FramebufferTextureMultiviewLayeredANGLE(enum target,
enum attachment,
uint texture,
int level,
int baseViewIndex,
sizei numViews);
can be used to attach a 2D texture array object as one of the logical
buffers of a framebuffer object which is to be used for layered
multi-view rendering.
basicViewIndex specifies the View-id offset.
numViews specifies the number of views associated with the attachment.
Any <Draw> command, while a layered multi-view framebuffer is bound,
has the same effect as:
for( int id = 0; i < numViews; id++ ) {
for ( framebufferAttachment : framebuffer.getAllAttachments() )
{
attachment = framebufferAttachment.attachment
texture = framebufferAttachment.texture
level = framebufferAttachment.level
baseViewIndex = framebufferAttachment.baseViewIndex
FramebufferTextureLayer( target, attachment, texture, level,
baseViewIndex + id );
}
SelectView( id );
<Draw>
}
Errors:
An INVALID_ENUM error is generated if target is not DRAW_FRAMEBUFFER,
READ_FRAMEBUFFER, or FRAMEBUFFER.
An INVALID_OPERATION error is generated if attachment is
COLOR_ATTACHMENTm where m is greater than or equal to the value
of MAX_COLOR_ATTACHMENTS.
An INVALID_ENUM error is generated if attachment is not one of
the attachments in table 4.6, and attachment is not
COLOR_ATTACHMENTm where m is greater than or equal to the value
of MAX_COLOR_ATTACHMENTS.
An INVALID_OPERATION error is generated if zero is bound to target.
An INVALID_VALUE error is generated if texture is not zero, and
level is less than zero or greater than log2 of the value of
MAX_TEXTURE_SIZE.
An INVALID_OPERATION error is generated if texture is not zero,
and does not name an existing texture object of type TEXTURE_2D_ARRAY.
An INVALID_OPERATION error is generated if texture is not zero,
and names a texture with a compressed texture format.
An INVALID_VALUE error is generated if texture is not zero, and
baseViewIndex+numViews is greater than GL_MAX_ARRAY_TEXTURE_LAYERS.
An INVALID_VALUE error is generated if texture is not zero, and
numViews is less than 1 or greater than MAX_VIEWS_ANGLE.
An INVALID_VALUE error is generated if texture is not zero, and
baseViewIndex is less than 0.
The command
void FramebufferTextureMultiviewSideBySideANGLE(enum target,
enum attachment,
uint texture,
int level,
sizei numViews,
const int *viewportOffsets);
can be used to attach a 2D texture object as one of the logical buffers
of a framebuffer object which is to be used for side-by-side multi-view
rendering.
numViews specifies the number of views associated with the attachment.
viewportOffsets specifies the address of an array of integers containing
the x and y viewport offset of each view.
Any <Draw> command, while a side-by-side multi-view framebuffer is bound,
has the same effect as:
// Retrieve viewport and scissor state.
Rectangle viewport
GetIntegerv(VIEWPORT, viewport)
Rectangle scissor
GetIntegerv(SCISSOR_BOX, scissor)
for ( int id = 0; id < numViews; id++ )
{
// Setup view state.
for ( framebufferAttachment : framebuffer.getAllAttachments() )
{
attachment = framebufferAttachment.attachment
texture = framebufferAttachment.texture
level = framebufferAttachment.level
FramebufferTexture2D( target, attachment, TEXTURE_2D, texture,
level )
}
Viewport(viewport.x + viewportOffsets[id].x,
viewport.y + viewportOffsets[id].y,
viewport.width, viewport.height)
Scissor(scissor.x + viewportOffsets[id].x,
scissor.y + viewportOffsets[id].y,
scissor.width, scissor.height)
SelectView(id)
// Draw.
<Draw>
}
// Restore viewport and scissor state.
Viewport(viewport.x, viewport.y, viewport.width, viewport.height)
Scissor(scissor.x, scissor.y, scissor.width, scissor.height)
Errors:
An INVALID_ENUM error is generated if target is not DRAW_FRAMEBUFFER,
READ_FRAMEBUFFER, or FRAMEBUFFER.
An INVALID_OPERATION error is generated if attachment is
COLOR_ATTACHMENTm where m is greater than or equal to the value
of MAX_COLOR_ATTACHMENTS.
An INVALID_ENUM error is generated if attachment is not one of
the attachments in table 4.6, and attachment is not
COLOR_ATTACHMENTm where m is greater than or equal to the value
of MAX_COLOR_ATTACHMENTS.
An INVALID_OPERATION error is generated if zero is bound to target.
An INVALID_VALUE error is generated if texture is not zero and
level is less than zero or greater than log2 of the value of
MAX_TEXTURE_SIZE.
An INVALID_OPERATION error is generated if texture is not zero,
and does not name an existing texture object of type TEXTURE_2D.
An INVALID_OPERATION error is generated if texture is not zero,
and names a texture with a compressed texture format.
An INVALID_VALUE error is generated if texture is not zero, and
numViews is less than 1 or greater than MAX_VIEWS_ANGLE.
An INVALID_VALUE error is generated if texture is not zero, and
any of the first numViews * 2 values in viewportOffsets is negative.
Having overlapping scissor rectangles after viewport offsets are
applied causes undefined behavior.
"
Add the following bullet points in the list after
"Effects of Attaching a Texture Image":
" * The value of FRAMEBUFFER_ATTACHMENT_TEXTURE_NUM_VIEWS_ANGLE is
set to <numViews>.
* The value of FRAMEBUFFER_ATTACHMENT_TEXTURE_MULTIVIEW_LAYOUT_ANGLE
is set to:
** FRAMEBUFFER_MULTIVIEW_SIDE_BY_SIDE_ANGLE if the texture
is attached via a call to
FramebufferTextureMultiviewSideBySideANGLE.
** FRAMEBUFFER_MULTIVIEW_LAYERED_ANGLE if the texture is
attached via a call to FramebufferTextureMultiviewLayeredANGLE.
** NONE otherwise.
* The value of FRAMEBUFFER_ATTACHMENT_TEXTURE_BASE_VIEW_INDEX_ANGLE
is set to <baseViewIndex> if FramebufferTextureMultiviewLayeredANGLE
is called. Otherwise, the default value remains.
* The value of FRAMEBUFFER_ATTACHMENT_TEXTURE_VIEWPORT_OFFSETS_ANGLE
is set to <viewportOffsets>.
"
Modify section 4.4.4.1 (Framebuffer Attachment Completeness), p. 213
Add a bullet point to the end of the list:
"If the value of FRAMEBUFFER_ATTACHMENT_OBJECT_TYPE is TEXTURE and
the value of FRAMEBUFFER_ATTACHMENT_OBJECT_NAME names a two-dimensional
array texture, then the sum of FRAMEBUFFER_ATTACHMENT_TEXTURE_NUM_VIEWS_ANGLE
and FRAMEBUFFER_ATTACHMENT_TEXTURE_BASE_VIEW_INDEX_ANGLE must be less
than the number of layers in the texture."
Modify section 4.4.4.2 (Whole Framebuffer Completeness), p. 214
Add a bullet point after "{ FRAMEBUFFER_INCOMPLETE_MULTISAMPLE }":
"
* All populated framebuffer attachments have the same number of views,
same multi-view layout and same viewport offsets.
{ FRAMEBUFFER_INCOMPLETE_VIEW_TARGETS_ANGLE }
"
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 6.1.13 (Framebuffer Object Queries), p. 242
Add a bullet point to the first list:
" * If <pname> is FRAMEBUFFER_ATTACHMENT_TEXTURE_NUM_VIEWS_ANGLE,
then <params> will contain the number of views for the specified
attachment.
* If <pname> is FRAMEBUFFER_ATTACHMENT_TEXTURE_VIEWPORT_OFFSETS_ANGLE,
then <params> will contain the viewport offsets for the specified
attachment. It is undefined behavior to provide an array with size
less than 2 x <num views>.
* If <pname> is FRAMEBUFFER_ATTACHMENT_TEXTURE_MULTIVIEW_LAYOUT_ANGLE,
then <params> will contain FRAMEBUFFER_MULTIVIEW_SIDE_BY_SIDE_ANGLE,
FRAMEBUFFER_MULTIVIEW_LAYERED_ANGLE or NONE.
* If <pname> is FRAMEBUFFER_ATTACHMENT_TEXTURE_BASE_VIEW_INDEX_ANGLE,
then <params> will contain the base view index offset for the
specified attachment."
Changes to table 6.14, p. 259 (Framebuffer (state per attachment point))
Get Value Type Get Command Value Description Sec.
--------- ----- ----------- ------- ----------- ----
FRAMEBUFFER_ATTACHMENT_TEXTURE_NUM_VIEWS_ANGLE Z+ GetFramebuffer-
Attachment- 1 Number of views 4.4.2.4
Parameteriv
FRAMEBUFFER_ATTACHMENT_TEXTURE_VIEWPORT_OFFSETS_ANGLE n x Z^{2} GetFramebuffer- 0,0 Viewport offset 4.4.2.4
Attachment- of each view
Parameteriv
FRAMEBUFFER_ATTACHMENT_TEXTURE_MULTIVIEW_LAYOUT_ANGLE Z+ GetFramebuffer- NONE Layout type - 4.4.2.4
Attachment- non-multiview,
Parameteriv layered or
side-by-side
FRAMEBUFFER_ATTACHMENT_TEXTURE_BASE_VIEW_INDEX_ANGLE Z GetFramebuffer- 0 Base view offset 4.4.2.4
Attachment-
Parameteriv
Changes to table 6.28, p. 273 (Implementation Dependent Values):
Add the following entry after MAX_VIEWPORT_DIMS:
Get Value Type Get Command Value Description Sec.
--------- ----- ----------- ------- ----------- ----
MAX_VIEWS_ANGLE Z+ GetIntegerv 4 Maximum number of 4.4
views
Additions to the OpenGL ES 3.0 Shading Language Specification
Including the following line in a shader can be used to control the
language features described in this extension:
#extension GL_OVR_multiview : <behavior>
where <behavior> is as specified in section 3.5.
New preprocessor #defines are added to the OpenGL Shading Language:
#define GL_OVR_multiview 1
Modify section 4.3.8.1 (Input Layout Qualifiers)
Replace the first sentence by:
"Input variable declarations in the vertex shader can have input
layout qualifiers."
Add the following text just before the sentence "Fragment shaders
cannot ...":
"The number of views to which to the program must render to is
specified through the num_views layout qualifier:
layout-qualifier-id
num_views = integer-constant
For example, the following declaration in a vertex shader
layout (num_views=4) in;
is used to specify that the program renders to 4 views.
If num_views is less than 1 or greater than the maximum number of
supported views, a compile-time error is generated.
If the layout qualifier is declared multiple times and not all
declarations specify the same number of views, a compile-time error
is generated."
Modify section 7.1 (Vertex Shader Special Variables)
Add to the list of built-ins just after the entry for gl_InstanceID:
" in highp uint gl_ViewID_OVR;"
Add a description for gl_ViewID_OVR just after the paragraph for
gl_InstanceID:
"The variable gl_ViewID_OVR is a vertex shader input variable that
holds the view id which designates the view which the current
vertex is being processed for."
Modify section 7.2 (Fragment Shader Special Variables)
Add to the list of built-ins just after the entry for gl_InstanceID:
" in highp uint gl_ViewID_OVR;"
Add a description for gl_ViewID_OVR just after the paragraph for
gl_PointCoord:
"The variable gl_ViewID_OVR is a fragment shader input variable that
holds the view id which designates the view which the current
fragment is being processed for."
Additions to Chapter 10 of the OpenGL ES 3.1 Specification
(Vertex Specification and Drawing Commands)
Modify section 10.5 (Drawing Commands Using Vertex Arrays), p. 254
Append to the list of errors for the command DrawArraysIndirect:
"* An INVALID_OPERATION if the number of views in the draw framebuffer
is greater than 1."
Append to the list of errors for the command DrawElementsIndirect:
"* An INVALID_OPERATION if the number of views in the draw framebuffer
is greater than 1."
Additions to the AGL/EGL/GLX/WGL Specifications
None
Interactions with EXT_disjoint_timer_query
An INVALID_OPERATION error is generated by any Draw* command and the Clear
command if there is an active query object for target TIME_ELAPSED_EXT and
the number of views in the draw framebuffer is greater than 1.
Errors
None
Issues
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