Author: eilemann@gmail.com
State: Implemented in 0.9.1
Overview
This features adds support for a new type of decomposition and recomposition, whereby each contributing channel renders one or multiple subsamples for full-scene anti-aliasing (FSAA) or depth-of-field (DOF).
Applications might already do multi-pass software FSAA/DOF, either during rendering or when the application is idle. Equalizer does not yet have a notion of idle/non-idle rendering.
Design
The application will do the adding of the frustum jitter, since it is the one which knows how many FSAA and/or DOF samples are desired. Therefore it needs to know in Channel::frameDraw which sample out of how many it should render.
The default implementation of Channel::applyFrustum will use the subpixel sample description to compute an FSAA jitter using a pre-defined lookup table. It will add this jitter to the frustum supplied by getFrustum.
Applications which have their own SWAA settings will use the subpixel sample description to calculate how many passes with which samples have to be rendered, e.g., if it desires to render 16 samples on a 4-time decomposition, the application will render 4 passes out of a 16-value jitter lookup table on each channel.
It is the application's responsibility to provide a blended result of the sub-passes on each channel. This should not be an overhead, since the application could already compute the accumulation and averaging before.
Compositing
API
class SubPixel
{
public:
uint32_t index;
uint32_t size;
}
vmml::Vector2f Channel::getJitter() const;
vmml::Vector2i Channel::getSubpixel() const;
File Format
compound
{
subpixel [ index size ]
}
Implementation
Idle SWAA in eqPly
class FrameData
bool _idleMode // idle AA mode
class Config
uint32_t _nbFramesAA // number of frames left
class Channel
Accum* _accum // accumulation buffer
uint32_t _jitterStep // current jitter step decrementing
uint32_t _totalSteps // total steps to be done
uint32_t _subpixelStep // number of ressources (subpixel.size)
bool _needsTransfer // combining idle AA with AA compound
PixelViewport _currentPVP // current saved pvp
-------------------------------------------------------------------
Config::startFrame
if view is idle AA
assert( nbFramesAA > 0 )
--nbFramesAA
set idleMode
else
nbFrames = 0
clear idleMode
commit frame data
Config::handleEvent
event = get IDLE_AA event
nbFramesAA = MAX( nbFramesAA, event->jitter )
Channel::frameStart
if view is not in idle AA mode
clear accum
reset idle AA
Channel::frameViewStart
save _currentPVP
Channel::frameDraw
[...]
_subpixelStep = MAX( _subpixelStep, getSubPixel().size )
set _needsTransfer
Channel::frameAssemble
if getPVP != _currentPVP
if accum doesn't use an FBO
warning, idle AA not implemented
stop idle AA
do normal assembly
set _needsTransfer
else
if all input frames have SubPixel::ALL
do normal assembly
set _needsTransfer
else
for each input frame
assemble each frame with subpixel decomp
accumulate
clear _needsTransfer
Channel::frameViewFinish
if PVP has changed
resize accum buffer
clear accum
reset idle AA
else if idle mode && _needsTransfer
if first idle step
reset accum buffer
accumulate back buffer to accum buffer
display average result in back buffer
Channel::frameFinish
if idle mode && _jitterStep > 0
_jitterStep -= subpixelStep
create IDLE_AA event
send event to the config
Channel::applyFrustum
if idle mode && _jitterStep > 0
jitter = _getJitter();
apply jitter vector to frustum
else
do normal apply frustum
Channel::_getJitterStep
idx = channelID * _totalSteps;
idx += ( _jitterStep * primeNumber[channelID] ) % subset_size
return ( idx % sampleSize, idx / sampleSize )
Channel::_getJitter
compute pixel size and subpixel size on near plane (frustum)
generate random sample position in _getJitterStep() subpixel
AA compound in Equalizer
AA compounds without idle AA:
eq::Channel::applyFrustum / applyOrtho
-> add jitter
eq::Channel::frameAssemble
Step 1: Do accumulation using GPU:
for each jitter decomp in input frames
assemble all input frames with jitter decomp
accumulate result
return result
Step 2: Opt: Do accumulate using CPU (later)
AA compounds with idle AA:
See also Issue 6.
-> extend compositor functions so the accumulation buffer (and state?) can be
given as parameter
Server
loader add subpixel token Compound::InheritData add subpixel param Compound::updateInheritData update subpixel CompoundUpdateOutput::_updateOutput update subpixel ChannelUpdateVisitor::_setupRenderContext update subpixel FrameData::setSubPixel
Client
FrameData::Data
add subpixel param
Channel::getSubPixel
Channel::applyFrustum
if subpixel decomp
lookup on precomputed jitter tables
if no table is found
compute the sample randomly
apply the jitter vector
Compositor::obtainAcum
get accum object from ObjectManager
if accum doesn't exist
create new accum object
else
resize accum
Compositor::assembleFramesSorted/Unsorted
if input frames have different subpixel decomp
if accum doesn't exist
obtain accum from compositor
clear accum
extract similar subpixel decomp
assemble frames (recursion on assembleFramesSorted/Unsorted)
accumulate frames
display result
[...]
Issues
1. Do we need a one-dimensional or two-dimensional subpixel description for each source channel?
This depends on Q2. My feeling is a one-dimensional attribute is easier.
2. How do I compute my current jitter area?
The number of jitter areas, i.e, the number of FSAA or DOF samples, is an application parameter. The current jitter area within each Channel::frameDraw is a function of the current idle step and the channel's subpixel description.
Open Issue: the function itself. The jitter values for all channels in the first pass should be evenly distributed over the total subpixel grid.
Idea: Divide the sample grid into the number of channels to get a subset of pixels for each channel. For each pass, compute (pass_number * rnd_prime_number) % size to get kind of a randomized distribution. The size parameter is the size of the pixel subset for the current channel.
3. How do I disable FSAA when it's not supported?
Depending on the OpenGL version, we run either the glAccum method either the FBO's one. On MacOSX, a different implementation of glAccum is needed.
4. How do I compute the jitter steps for FSAA compound?
The destination channel asks for a new frame instead that the config starts a new frame itself. Each destination channel sends an event to the config which takes the maximum number of steps needed and enables to start a new frame.
5. How do I decrement the jitter steps done in the current frame?
The destination channel might render 0..n jitter steps and receive 0..n jitter steps as input frames during compositing.
We could assume that a subpixel decomposition parameter is set for the destination channel. If the destination channel does a frameDraw, he will decrement the jitter step by the subpixel decomposition size in frameDraw, otherwise he will decrement it by the subpixel decomposition size of the input frames in frameAssemble:
Channel::frameStart
_subpixelSteps = 0;
Channel::frameDraw
_subpixelSteps = EQ_MAX( _subpixelSteps, subpixel.size );
Channel::frameAssemble
for each input frame
_subpixelSteps = EQ_MAX( _subpixelSteps, frame.subpixel.size );
Channel::frameFinish
_jitterSteps -= _subpixelSteps;
send event
6. How does the accumulation in frameAssemble work together with the one in frameViewFinish?
Without any scalability, each destination channel accumulates in idle mode the results of different frames into an accumulation buffer. With scalability, frameAssemble might accumulate the results of different, jittered input frames.
A simple, but non-optimal solution is to assemble and average all jitter steps in frameAssemble, and to transfer the result into the accumulation buffer n times in frameViewFinish:
Channel::frameAssemble
accumulate all input frames in separate accum buffer
return accum buffer to frame buffer
Channel::frameViewFinish
copy frame buffer _subpixelSteps times into accum buffer
_stepsDone += _subpixelSteps;
return accum buffer
In the optimal case, frameAssemble and frameViewFinish should share the accumulation buffer:
Channel::frameDraw
set _needsTransfer
Channel::frameViewStart
save current pvp
Channel::frameAssemble
if( current pvp != saved pvp )
use separate accum buffer
return accum buffer after assembly
set _needsTransfer
Q: what if glAccum is used? Disable idle AA for this channel?
if( all input frames have Subpixel::ALL )
do normal assembly
set _needsTransfer
else if for each jitter decomp in input frames
assemble all input frames with jitter decomp
accumulate result
clear _needsTransfer
Channel::frameViewFinish
if _needsTransfer
accumulate FB into accum buffer
return accum buffer
