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Difference between revisions of "Compositor"

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== Features ==
 
== Features ==
  
* Completely independent of other parts of the simulator, i.e. it's part of SimGear and can be used in a standalone fashion if needed, ala Canvas.
+
* Completely independent of other parts of the simulator, i.e. it's part of [[SimGear]] and can be used in a standalone fashion if needed, ala Canvas.
* Although independent, its aim is to be fully compatible with the current rendering framework in FG. This includes the Effects system, CameraGroup, Rembrandt and ALS (and obviously the Canvas).
+
* Although independent, its aim is to be fully compatible with the current rendering framework in FG. This includes the [[Effects]] system, [[Howto:Configure camera view windows|CameraGroup]], [[Rembrandt]] and [[ALS]] (and obviously the [[Canvas]]).
 
* Its functionality overlaps Rembrandt: what can be done with Rembrandt can be done with the Compositor, but not vice versa.
 
* Its functionality overlaps Rembrandt: what can be done with Rembrandt can be done with the Compositor, but not vice versa.
* Fully configurable via an XML interface without compromising performance (ala Effects, using PropertyList files).
+
* Fully configurable via an XML interface without compromising performance (ala Effects, using [[PropertyList XML File|PropertyList files]]).
 
* Flexible, expandable and compatible with modern graphics.
 
* Flexible, expandable and compatible with modern graphics.
 
* It doesn't increase the hardware requirements, it expands the hardware range FG can run on. People with integrated GPUs (Intel HD etc) can run a Compositor with a single pass that renders directly to the screen like before, while people with more powerful cards can run a Compositor that implements deferred rendering, for example.
 
* It doesn't increase the hardware requirements, it expands the hardware range FG can run on. People with integrated GPUs (Intel HD etc) can run a Compositor with a single pass that renders directly to the screen like before, while people with more powerful cards can run a Compositor that implements deferred rendering, for example.
* Static branching support. Every pipeline element can be enabled/disabled at startup via a <condition> block.
+
* Static branching support. Every pipeline element can be enabled/disabled at startup via a [[Conditions|<condition> block]].
  
 
== How to enable the Compositor ==
 
== How to enable the Compositor ==
  
 
Currently the Compositor can only be enabled at compile time via the <code>-DENABLE_COMPOSITOR=ON</code> CMake flag in FlightGear. SimGear doesn't require any extra parameters. Once you have a binary with the Compositor enabled and you run it, you will be presented with the default rendering pipeline. At the time of writing, this is the low spec rendering pipeline. If you want to try the ALS pipeline, start FlightGear with the command line argument: <code>--compositor=Compositor/ALS/als</code>
 
Currently the Compositor can only be enabled at compile time via the <code>-DENABLE_COMPOSITOR=ON</code> CMake flag in FlightGear. SimGear doesn't require any extra parameters. Once you have a binary with the Compositor enabled and you run it, you will be presented with the default rendering pipeline. At the time of writing, this is the low spec rendering pipeline. If you want to try the ALS pipeline, start FlightGear with the command line argument: <code>--compositor=Compositor/ALS/als</code>
 +
 +
If you want to enable shadows on all objects in the ALS pipeline use these options as a startup parameters (in QT GUI or in the commandline) <code>--prop:bool:/sim/rendering/als/shadows/enabled=true</code> and <code>--prop:int:/sim/rendering/als/shadows/sun-atlas-size=2048</code>. If you feel like the shadows are too low-quality (specially in the cockpit), increase the shadow resolution to 4096 or 8192 instead of 2048.
  
 
== Notes for aircraft developers ==
 
== Notes for aircraft developers ==
Line 84: Line 86:
 
The Compositor introduces a new way of defining lights that is renderer agnostic, so every rendering pipeline will be able to access the lights that have been implemented like this. As of 2019/11, the only pipeline that supports dynamic lights is the ALS pipeline. The resulting light volumes can be visualized for debugging purposes by setting the property <tt>/sim/debug/show-light-volumes</tt> to true.
 
The Compositor introduces a new way of defining lights that is renderer agnostic, so every rendering pipeline will be able to access the lights that have been implemented like this. As of 2019/11, the only pipeline that supports dynamic lights is the ALS pipeline. The resulting light volumes can be visualized for debugging purposes by setting the property <tt>/sim/debug/show-light-volumes</tt> to true.
  
{|cellpadding=20|
+
{|cellpadding=10|
 
|valign=top style="width: 20%;"|
 
|valign=top style="width: 20%;"|
 
<syntaxhighlight lang="xml">
 
<syntaxhighlight lang="xml">
Line 123: Line 125:
 
     <q>0.032</q>
 
     <q>0.032</q>
 
   </attenuation>
 
   </attenuation>
   <exponent>5</exponent>
+
   <spot-exponent>5</spot-exponent>
   <cutoff>40</cutoff>
+
   <spot-cutoff>40</spot-cutoff>
 
   <range-m>50</range-m>
 
   <range-m>50</range-m>
 
</light>
 
</light>
 
</syntaxhighlight>
 
</syntaxhighlight>
 
|valign=top style="width: 80%;"|
 
|valign=top style="width: 80%;"|
* <tt>'''name'''</tt>. An <code><animation></code> will be able to reference the light by this name. Most animations will work as expected (rotate, translate, spin etc).
+
* <tt>'''name'''</tt>. An {{tag|animation}} will be able to reference the light by this name. Most animations will work as expected (rotate, translate, spin etc).
 
* <tt>'''type'''</tt>. <tt>spot</tt> or <tt>point</tt>.
 
* <tt>'''type'''</tt>. <tt>spot</tt> or <tt>point</tt>.
 
* <tt>'''position'''</tt>. The position of the light source in model space and in meters.
 
* <tt>'''position'''</tt>. The position of the light source in model space and in meters.
Line 178: Line 180:
 
</model>
 
</model>
 
</syntaxhighlight>
 
</syntaxhighlight>
* Unlike in Rembrandt, polygons facing the Sun are the ones used to generate the shadow map. That means that single sided or non-closed objects should be rendered correctly.
+
* Unlike in Rembrandt, polygons facing the Sun are the ones used to generate the shadow map, so single sided surfaces and non-closed objects should be rendered correctly.
  
 
== Pipelines ==
 
== Pipelines ==
Line 199: Line 201:
 
* Should the terrain cast shadows? The terrain is rarely steep enough to cast shadows. Apart from that, the terrain in FlightGear messes with automatic near/far computations for the shadow passes since the geometry is not tessellated enough. Also, the terrain LOD is not good enough to have decent cull times at far cascades.
 
* Should the terrain cast shadows? The terrain is rarely steep enough to cast shadows. Apart from that, the terrain in FlightGear messes with automatic near/far computations for the shadow passes since the geometry is not tessellated enough. Also, the terrain LOD is not good enough to have decent cull times at far cascades.
 
* Adding a "internal only" shadow flag for aircraft developers. This allows farther shadow cascades to cull complex objects that are only visible in the nearest cascades. (Very important optimization for aircrafts with complex cockpit geometry).
 
* Adding a "internal only" shadow flag for aircraft developers. This allows farther shadow cascades to cull complex objects that are only visible in the nearest cascades. (Very important optimization for aircrafts with complex cockpit geometry).
 +
* Vegetation shadows will be done by the "legacy" method currently in use. Shadow mapping on vegetation is much more expensive in terms of performance and the current algorithm does the job well enough. <ref>https://forum.flightgear.org/viewtopic.php?f=47&p=357606</ref>
  
 
==== Post-processing ====
 
==== Post-processing ====
Line 213: Line 216:
  
 
* Using RenderBins. After a single scene cull traversal, surfaces which belong to a special RenderBin type (DepthSortedBin) are removed or moved to another camera. This is how Rembrandt does it and it is the most backwards compatible approach since RenderBins can be changed directly inside Effects.
 
* Using RenderBins. After a single scene cull traversal, surfaces which belong to a special RenderBin type (DepthSortedBin) are removed or moved to another camera. This is how Rembrandt does it and it is the most backwards compatible approach since RenderBins can be changed directly inside Effects.
 
<syntaxhighlight lang="cpp">
 
void removeTransparentBins(simgear::EffectCullVisitor *cv,
 
                          osgUtil::RenderBin::RenderBinList &transparent_bins)
 
{
 
    osgUtil::RenderStage *stage = cv->getRenderStage();
 
    osgUtil::RenderBin::RenderBinList &rbl = stage->getRenderBinList();
 
    for (auto rbi = rbl.begin(); rbi != rbl.end(); ) {
 
        if (rbi->second->getSortMode() == osgUtil::RenderBin::SORT_BACK_TO_FRONT) {
 
            transparent_bins.insert(std::make_pair(rbi->first, rbi->second));
 
            rbl.erase(rbi++);
 
        } else {
 
            ++rbi;
 
        }
 
    }
 
}
 
</syntaxhighlight>
 
 
* Using cull masks. Two separate traversals are done: one for opaque objects and another for translucent objects. This requires offering aircraft developers another way of tagging a surface as transparent. A trivial approach would be to add a new <animation> type called 'transparent', but that wouldn't be backwards compatible. Maybe we can add some kind of system where we can change cull masks inside Effects? Would that be too hacky or out of place?
 
* Using cull masks. Two separate traversals are done: one for opaque objects and another for translucent objects. This requires offering aircraft developers another way of tagging a surface as transparent. A trivial approach would be to add a new <animation> type called 'transparent', but that wouldn't be backwards compatible. Maybe we can add some kind of system where we can change cull masks inside Effects? Would that be too hacky or out of place?
  
 
== Creating a custom rendering pipeline ==
 
== Creating a custom rendering pipeline ==
  
Since the Compositor is completely data-driven, new rendering pipelines can be created by writing a custom XML pipeline definition. This section tries to document most of the available parameters, but the best and most up-to-date resource is the Compositor parsing code in SimGear ({{simgear file|simgear/scene/viewer}}).
+
Since the Compositor is completely data-driven, new rendering pipelines can be created by writing a custom XML pipeline definition. This section tries to document most of the available parameters, but the best and most up-to-date resource is the Compositor parsing code in SimGear ({{simgear file|simgear/scene/viewer}}). See existing pipelines in {{fgdata file|Compositor}} for practical examples on how to use these parameters.
  
 
=== Buffers ===
 
=== Buffers ===
  
A buffer represents a texture or, more generically, a region of GPU memory. It can have the following parameters:
+
A buffer represents a texture or, more generically, a region of GPU memory.
  
; name
+
{| class="wikitable" style="text-align: center; font-size: 85%; width: auto; table-layout: fixed;
: Passes will be able to address the buffer by this name.
+
! scope="col" | Parameter Name
; type
+
! scope="col" | Optional
: Any texture type allowed by OpenGL: 1d, 2d, 2d-array, 2d-multisample, 3d, rect or cubemap.
+
! scope="col" | Value
; width
+
! scope="col" | Default Value
: Texture width. It's possible to write 'screen' to use the physical viewport width.
+
! scope="col" | Description
; screen-width-scale (Optional)
+
|-
: If 'screen' was used, this controls the width scaling factor.
+
! scope="row"| <tt>name</tt>
; height
+
| {{No}}
: Texture height. It's possible to write 'screen' to use the physical viewport height.
+
| string
; screen-height-scale (Optional)
+
|
: If 'screen' was used, this controls the height scaling factor.
+
| Passes will be able to address the buffer by this name
; depth
+
|-
: Texture depth.
+
! scope="row"| <tt>type</tt>
; format
+
| {{No}}
: Specifies the texture format. It corresponds to the ''internalformat'', ''format'' and ''type'' arguments of the OpenGL function ''glTexImage2D''. See {{simgear file|simgear/scene/viewer/CompositorBuffer.cxx}} for the latest available values.
+
| <tt>1d, 2d, 2d-array, 2d-multisample, 3d, rect, cubemap</tt>
; min-filter and mag-filter (Optional)
+
|
: They change the minification and magnification filtering respectively. Possible values are: linear, linear-mipmap-linear, linear-mipmap-nearest, nearest, nearest-mipmap-linear and nearest-mipmap-nearest. The default value for both filters is linear.
+
| Any texture type allowed by OpenGL
; wrap-s, wrap-t and wrap-r (Optional)
+
|-
: They change the wrap mode for each coordinate. Possible values are: clamp, clamp-to-edge, clamp-to-border, repeat and mirror. The default value for every coordinate is clamp-to-border.
+
! scope="row"| <tt>width</tt>
; condition (Optional)
+
| {{No}}
: A valid boolean condition to enable the buffer at startup (doesn't work at runtime).
+
| Any unsigned integer or <tt>screen</tt> to use the physical viewport width. The <code><property></code> tag can also be used to use a property value
 
+
|
A typical [[PropertyList XML File|property tree structure]] describing a buffer may be as follows:
+
| Texture width
 
+
|-
<syntaxhighlight lang="xml">
+
! scope="row"| <tt>screen-width-scale</tt>
<buffer>
+
| {{Yes}}
  <name>color</name>
+
| float
  <type>2d</type>
+
| <tt>1.0</tt>
  <width>screen</width>
+
| If <tt>screen</tt> was used, this controls the width scaling factor
  <height>screen</height>
+
|-
  <screen-width-scale>1.5</screen-width-scale>
+
! scope="row"| <tt>height</tt>
  <screen-height-scale>1.5</screen-height-scale>
+
| {{No}}
  <internal-format>rgba8</internal-format>
+
| Any unsigned integer or <tt>screen</tt> to use the physical viewport height. The <code><property></code> tag can also be used to use a property value
  <source-format>rgba</source-format>
+
|
  <source-type>ubyte</source-type>
+
| Texture height
  <min-filter>nearest-mipmap-nearest</min-filter>
+
|-
  <mag-filter>nearest-mipmap-nearest</mag-filter>  
+
! scope="row"| <tt>screen-height-scale</tt>
  <wrap-s>repeat</wrap-s>
+
| {{Yes}}
  <wrap-t>repeat</wrap-t>
+
| float
</buffer>
+
| <tt>1.0</tt>
</syntaxhighlight>
+
| If <tt>screen</tt> was used, this controls the height scaling factor
 +
|-
 +
! scope="row"| <tt>depth</tt>
 +
| {{No}}
 +
| Any unsigned integer. The <code><property></code> tag can also be used to use a property value
 +
|
 +
| Texture depth
 +
|-
 +
! scope="row"| <tt>format</tt>
 +
| {{Yes}}
 +
| See {{simgear file|simgear/scene/viewer/CompositorBuffer.cxx}} for the latest available values
 +
| <tt>rgba8</tt>
 +
| Specifies the texture format. It corresponds to the ''internalformat'', ''format'' and ''type'' arguments of the OpenGL function ''glTexImage2D''
 +
|-
 +
! scope="row"| <tt>min-filter, mag-filter</tt>
 +
| {{Yes}}
 +
| <tt>linear, linear-mipmap-linear, linear-mipmap-nearest, nearest, nearest-mipmap-linear, nearest-mipmap-nearest</tt>
 +
| <tt>linear</tt>
 +
| Change the minification and magnification filtering respectively
 +
|-
 +
! scope="row"| <tt>wrap-s, wrap-t, wrap-r</tt>
 +
| {{Yes}}
 +
| <tt>clamp, clamp-to-edge, clamp-to-border, repeat, mirror</tt>
 +
| <tt>clamp-to-border</tt>
 +
| They change the wrap mode for each coordinate
 +
|-
 +
! scope="row"| <tt>anisotropy</tt>
 +
| {{Yes}}
 +
| float
 +
| <tt>1.0</tt>
 +
|
 +
|-
 +
! scope="row"| <tt>border-color</tt>
 +
| {{Yes}}
 +
| vec4
 +
| <tt>(0.0f, 0.0f, 0.0f, 0.0f)</tt>
 +
|
 +
|-
 +
! scope="row"| <tt>shadow-comparison</tt>
 +
| {{Yes}}
 +
| bool
 +
| <tt>true</tt>
 +
|
 +
|-
 +
! scope="row"| <tt>shadow-texture-mode</tt>
 +
| {{Yes}}
 +
| <tt>luminance, intensity, alpha</tt>
 +
| <tt>luminance</tt>
 +
|
 +
|-
 +
! scope="row"| <tt>shadow-compare-func</tt>
 +
| {{Yes}}
 +
| <tt>never, less, equal, lequal, greater, notequal, gequal, always</tt>
 +
| <tt>lequal</tt>
 +
|
 +
|}
  
 
=== Passes ===
 
=== Passes ===
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A pass wraps around an [http://public.vrac.iastate.edu/vancegroup/docs/OpenSceneGraphReferenceDocs-3.0/a00089.html osg::Camera]. Passes all have some common parameters:
 
A pass wraps around an [http://public.vrac.iastate.edu/vancegroup/docs/OpenSceneGraphReferenceDocs-3.0/a00089.html osg::Camera]. Passes all have some common parameters:
  
; clear-color, clear-accum, clear-depth and clear-stencil
+
{| class="wikitable" style="text-align: center; font-size: 85%; width: auto; table-layout: fixed;
: Default values are black, black, 1.0 and 0 respectively.
+
! scope="col" | Parameter Name
; clear-mask
+
! scope="col" | Optional
: Controls the camera clear mask. Default value is "color depth".
+
! scope="col" | Value
; effect-scheme
+
! scope="col" | Default Value
: The pass will try to use the specified effect scheme to draw every object.
+
! scope="col" | Description
; condition
+
|-
: A valid boolean condition to enable the pass at startup (doesn't work at runtime).
+
! scope="row"| <tt>clear-color, clear-accum, clear-depth and clear-stencil</tt>
 +
| {{Yes}}
 +
| vec4
 +
| black, black, <tt>1.0</tt>, <tt>0</tt> respectively
 +
| Pass clear colors
 +
|-
 +
! scope="row"| <tt>clear-mask</tt>
 +
| {{Yes}}
 +
| <tt>color, stencil, depth, accum</tt>
 +
| <tt>color depth</tt>
 +
| Pass clear mask
 +
|-
 +
! scope="row"| <tt>effect-scheme</tt>
 +
| {{Yes}}
 +
| Valid effect scheme name
 +
| None
 +
| The pass will try to use the specified effect scheme to draw every object.
 +
|}
  
Passes can render to a buffer (Render to Texture), to several buffers (Multiple Render Targets) or directly to the framebuffer. This is accomplished by the <code><attachment/></code> tag. Possible parameters of an attachment are:
+
Passes can render to a buffer (Render to Texture), to several buffers (Multiple Render Targets) or directly to the framebuffer. This is accomplished by the <code><attachment></code> tag. Possible parameters of an attachment are:
  
; buffer
+
{| class="wikitable" style="text-align: center; font-size: 85%; width: auto; table-layout: fixed;
: The name of the buffer to output to.
+
! scope="col" | Parameter Name
; component
+
! scope="col" | Optional
: FBO attachment point. Possible values are color0 to color15, depth, stencil and depth-stencil.
+
! scope="col" | Value
; level (Optional)
+
! scope="col" | Default Value
: Controls the mip map level of the texture that is attached. Default value is 0.
+
! scope="col" | Description
; face (Optional)
+
|-
: Controls the face of texture cube map or z level of 3d texture. Default value is 0.
+
! scope="row"| <tt>buffer</tt>
; mipmap-generation (Optional)
+
| {{No}}
: Controls whether mipmap generation should be done for texture. Default value is false.
+
| Valid buffer name
; multisample-samples (Optional)
+
|
: MSAA samples. Default value is 0.
+
| The name of the buffer to output to
; multisample-color-samples (Optional)
+
|-
: MSAA color samples. Default value is 0.
+
! scope="row"| <tt>component</tt>
; condition
+
| {{No}}
: A valid boolean condition to enable the attachment at startup (doesn't work at runtime).
+
| <tt>color, color0</tt> to <tt>color15, depth, stencil, depth-stencil</tt>
 +
|
 +
| FBO attachment point
 +
|-
 +
! scope="row"| <tt>level</tt>
 +
| {{Yes}}
 +
| int
 +
| <tt>0</tt>
 +
| Mipmap level of the texture that is attached
 +
|-
 +
! scope="row"| <tt>face</tt>
 +
| {{Yes}}
 +
| int
 +
| <tt>0</tt>
 +
| Face of cube map texture or z-level of 3d texture
 +
|-
 +
! scope="row"| <tt>mipmap-generation</tt>
 +
| {{Yes}}
 +
| bool
 +
| <tt>false</tt>
 +
| Whether mipmap generation should be done for texture
 +
|-
 +
! scope="row"| <tt>multisample-samples</tt>
 +
| {{Yes}}
 +
| int
 +
| <tt>0</tt>
 +
| Multisample anti-aliasing (MSAA) samples
 +
|-
 +
! scope="row"| <tt>multisample-color-samples</tt>
 +
| {{Yes}}
 +
| int
 +
| <tt>0</tt>
 +
| Multisample anti-aliasing (MSAA) color samples
 +
|}
  
Passes can also receive buffers as input and use them in their shaders. This is accomplished by the <code><binding/></code> tag, which has the following parameters:
+
Passes can also receive buffers as input and use them in their shaders. This is accomplished by the <code><binding></code> tag, which has the following parameters:
  
; buffer
+
{| class="wikitable" style="text-align: center; font-size: 85%; width: auto; table-layout: fixed;
: The name of the buffer to bind.
+
! scope="col" | Parameter Name
; unit
+
! scope="col" | Optional
: The texture unit to place the texture on. Effects will be able to access the buffer on this texture unit.
+
! scope="col" | Value
; condition
+
! scope="col" | Default Value
: A valid boolean condition to enable the binding at startup (doesn't work at runtime).
+
! scope="col" | Description
 +
|-
 +
! scope="row"| <tt>buffer</tt>
 +
| {{No}}
 +
| Valid buffer name
 +
|
 +
| The name of the buffer to bind
 +
|-
 +
! scope="row"| <tt>unit</tt>
 +
| {{No}}
 +
| int
 +
|
 +
| The texture unit to place the texture on. Effects will be able to access the buffer on this texture unit
 +
|}
  
There are specific pass types, each with their own set of custom parameters:
+
There are specific pass types, each with their own set of custom parameters.
  
 
==== scene ====
 
==== scene ====
 
Renders the scene from the point of view given by the CameraGroup.
 
Renders the scene from the point of view given by the CameraGroup.
; cull-mask
+
{| class="wikitable" style="text-align: center; font-size: 85%; width: auto; table-layout: fixed;
: A 32 bit number that specifies the cull mask to be used. See <tt>simgear/scene/util/RenderConstants.hxx</tt> to know which bits enable what.
+
! scope="col" | Parameter Name
; z-near and z-far
+
! scope="col" | Optional
: They change the depth range to be used. If both of them are zero, the default Z range in the CameraGroup is used.
+
! scope="col" | Value
; clustered-forward
+
! scope="col" | Default Value
: Enables the use of clustered forward rendering for this pass.
+
! scope="col" | Description
; cubemap-face
+
|-
: Ignores the given view and projection matrices and uses a custom one that renders the scene as if it was seen from inside a cubemap looking towards the specified face.
+
! scope="row"| <tt>cull-mask</tt>
 +
| {{Yes}}
 +
| A 32 bit number. See {{simgear file|simgear/scene/util/RenderConstants.hxx}} to know which bits enable what
 +
| <tt>0xffffffff</tt>
 +
| Specifies the cull mask to be used in the underlying <tt>osg::Camera</tt>
 +
|-
 +
! scope="row"| <tt>z-near, z-far</tt>
 +
| {{Yes}}
 +
| int
 +
| Default Z range in the CameraGroup
 +
| They change the depth range to be used
 +
|-
 +
! scope="row"| <tt>cubemap-face</tt>
 +
| {{Yes}}
 +
| int
 +
| <tt>-1</tt> (don't use cubemap)
 +
| Ignores the given view and projection matrices and uses a custom one that renders the scene as if it was seen from inside a cubemap looking towards the specified face
 +
|}
  
 
==== quad ====
 
==== quad ====
 
Renders a fullscreen quad with an optional [[Effects|effect]] applied. Useful for screen space shaders (like SSAO, Screen Space Reflections or bloom) and deferred rendering.
 
Renders a fullscreen quad with an optional [[Effects|effect]] applied. Useful for screen space shaders (like SSAO, Screen Space Reflections or bloom) and deferred rendering.
; geometry
+
{| class="wikitable" style="text-align: center; font-size: 85%; width: auto; table-layout: fixed;
: Specifies the x, y, width and height of the fullscreen quad inside the viewport using normalized coordinates.
+
! scope="col" | Parameter Name
; effect
+
! scope="col" | Optional
: The quad will use this effect.
+
! scope="col" | Value
 +
! scope="col" | Default Value
 +
! scope="col" | Description
 +
|-
 +
! scope="row"| <tt>geometry</tt>
 +
| {{Yes}}
 +
| float values for <code><x>, <y>, <width>, <height></code>
 +
| <tt>0.0, 0.0, 1.0, 1.0</tt> respectively
 +
| Size of the fullscreen quad inside the viewport using normalized coordinates.
 +
|-
 +
! scope="row"| <tt>effect</tt>
 +
| {{Yes}}
 +
| Valid Effect file
 +
| None
 +
| This Effect will be applied to the quad geometry
 +
|}
  
 
==== shadow-map ====
 
==== shadow-map ====
 
Renders the scene from a light's point of view.
 
Renders the scene from a light's point of view.
; light-num
+
{| class="wikitable" style="text-align: center; font-size: 85%; width: auto; table-layout: fixed;
: The OpenGL light number to use for this shadow map.
+
! scope="col" | Parameter Name
; near-m and far-m
+
! scope="col" | Optional
: They specify the range of the shadow map.
+
! scope="col" | Value
 
+
! scope="col" | Default Value
Example XML for a ''scene'' type pass:
+
! scope="col" | Description
 
+
|-
<syntaxhighlight lang="xml">
+
! scope="row"| <tt>light-name</tt>
<pass>
+
| {{No}}
  <name>forward-lighting</name>
+
| Valid light name that exists in the scene graph
  <type>scene</type>
+
|
  <clear-color type="vec4d">0 0 0 0</clear-color>
+
| The name of the <tt>osg::LightSource</tt> to use for this shadow map
 
+
|-
  <clustered-forward/>
+
! scope="row"| <tt>near-m, far-m</tt>
 
+
| {{No}}
  <binding>
+
| Valid Effect file
    <buffer>shadowmap</buffer>
+
|
    <unit>10</unit>
+
| They specify the depth range of the shadow map
  </binding>
+
|}
  <attachment>
+
    <buffer>color</buffer>
+
    <component>color0</component>
+
    <multisample-samples>4</multisample-samples>
+
    <multisample-color-samples>4</multisample-color-samples>
+
  </attachment>
+
  <attachment>
+
    <buffer>depth</buffer>
+
    <component>depth</component>
+
  </attachment>
+
</pass>
+
</syntaxhighlight>
+
  
 
== TODO ==
 
== TODO ==
Line 382: Line 506:
 
* Bring back distortion correction.
 
* Bring back distortion correction.
 
* Some kind of versioning system to be able to make breaking changes in the future if/when the compositor is updated in any significant way, without people having to manually update their configs.
 
* Some kind of versioning system to be able to make breaking changes in the future if/when the compositor is updated in any significant way, without people having to manually update their configs.
* Bring back Canvas integration so aircraft devs have access to the rendering pipeline. This allows to render exterior views in cockpit displays etc.
+
* Bring back [[Howto:Canvas View Camera Element|Canvas integration]] so aircraft devs have access to the rendering pipeline. This allows to render exterior views in cockpit displays etc.
 
* Automatically calculate light source attenuation based on radius and radius based on attenuation.
 
* Automatically calculate light source attenuation based on radius and radius based on attenuation.
 +
* Add 1-bit transparency to shadow mapping (maybe even full blown transparency with multiple depth buffers?).
  
 
== Known Issues ==
 
== Known Issues ==
Line 389: Line 514:
 
* Setting a buffer scale factor different from 1.0 and rendering to it might not scale the splash screen correctly.
 
* Setting a buffer scale factor different from 1.0 and rendering to it might not scale the splash screen correctly.
 
* Clustered shading crashes FG if compiled under OSG 3.6. This is related to osg::TextureBuffer changing definition from OSG 3.4 to OSG 3.6 (Images vs BufferData).
 
* Clustered shading crashes FG if compiled under OSG 3.6. This is related to osg::TextureBuffer changing definition from OSG 3.4 to OSG 3.6 (Images vs BufferData).
 +
* Relative path Effects in aircrafts don't work. This is '''not''' permanent, they will work again once the Compositor replaces the legacy renderer.
 +
* EarthView doesn't work.
 +
* There is some kind of moiré pattern at certain sunlight angles (specially at dusk/dawn).
 +
* hud.eff doesn't work under the ALS pipeline.
 +
* Spotlights sometimes disappear at certain view angles.
 +
* Vegetation appears to flicker at long distances.
  
== Related ==
+
== References ==
=== Articles ===
+
{{Appendix}}
 +
 
 +
== Related content ==
 +
=== Wiki articles ===
 
* [[Uniform Buffer Objects]]
 
* [[Uniform Buffer Objects]]
 
* [[CompositeViewer Support]]
 
* [[CompositeViewer Support]]
 
* [[FlightGear CIGI Support (Common Image Generator Interface)]]
 
* [[FlightGear CIGI Support (Common Image Generator Interface)]]
=== Discussions ===
+
 
 +
=== Forum topics ===
 +
* {{forum link|t=36269|text=The Compositor}}
 
* {{forum link|t=35095|text=Clustered Forward Rendering}} (12/2018)
 
* {{forum link|t=35095|text=Clustered Forward Rendering}} (12/2018)
 
* {{forum link|t=33045|text=Getting started with RTT}}
 
* {{forum link|t=33045|text=Getting started with RTT}}
Line 403: Line 539:
 
* {{forum link|t=18905|text=Progress on synthetic terrain}}
 
* {{forum link|t=18905|text=Progress on synthetic terrain}}
 
* {{forum link|t=17184|text=Instruments with heightmaps}}
 
* {{forum link|t=17184|text=Instruments with heightmaps}}
 
 
{{Appendix}}
 
  
 
[[Category:Core development projects]]
 
[[Category:Core development projects]]

Latest revision as of 02:01, 5 December 2019

This article describes content/features that may not yet be available in the latest stable version of FlightGear (2018.3).
You may need to install some extra components, use the latest development (Git) version or even rebuild FlightGear from source, possibly from a custom topic branch using special build settings: -DENABLE_COMPOSITOR=ON.

This feature is scheduled for FlightGear 2019.2. 100}% completed

If you'd like to learn more about getting your own ideas into FlightGear, check out Implementing new features for FlightGear.


Compositor Framework
ALS Compositor pipeline.jpg
Started in 01/2018 (Available since FlightGear 2019.2)
Description Dynamic rendering pipeline configured via the property tree and XML
Contributor(s) Fernando García Liñán
Status Stable
Folders

The Compositor aims to bring multi-pass rendering to FlightGear. It encapsulates a rendering pipeline and exposes its parameters to a Property Tree interface. At startup, FlightGear reads the pipeline definition file for each physical viewport defined on the CameraGroup settings. If no Compositor file is specified for a physical camera, the one given by the --compositor= startup command will be used. If such startup option is not used either, FlightGear will look for a valid Compositor file in $FG_ROOT/Compositor/default.xml

The Compositor introduces a new dedicated fgdata directory for new/custom rendering pipelines: fgdata/Compositor.

Background

First discussed in 03/2012 during the early Rembrandt days, Zan (Lauri Peltonen) came up with a set of patches demonstrating how to create an XML-configurable rendering pipeline.

Back then, this work was considered to look pretty promising [1] and at the time plans were discussed to unify this with the ongoing Rembrandt implementation (no longer maintained).

Adopting Zan's approach would have meant that efforts like Rembrandt (deferred rendering) could have been implemented without requiring C++ space modifications, i.e. purely in Base package space.

Rembrandt's developer (FredB) suggested to extend the format to avoid duplicating the stages when you have more than one viewport, i.e. specifying a pipeline as a template, with conditions like in effects, and have the current camera layout refer the pipeline that would be duplicated, resized and positioned for each declared viewport [2]

Zan's original patches can still be found in his newcameras branches which allow the user to define the rendering pipeline in preferences.xml: FlightGear, SimGear.

At that point, it didn't have everything Rembrandt's pipeline needs, but most likely could be easily enhanced to support those things.

Basically, the original version added support for multiple camera passes, texture targets, texture formats, passing textures from one pass to another etc, while preserving the standard rendering line if user wants that. [3]

Since the early days of Zan's groundwork, providing the (hooks) infrastructure to enable base package developers to prototype, test and develop distinct rendering pipelines without requiring C++ space modifications has been a long-standing idea, especially after the Canvas system became available in early 2012, which demonstrated how RTT-rendering buffers (FBOs) could be set up, created and manipulated procedurally (i.e. at run-time) using XML, the property tree and Nasal scripting. [4]

The new Compositor is an improved re-implementation of Zan's original work using not just XML, but also properties and a handful of Canvas concepts.

Features

  • Completely independent of other parts of the simulator, i.e. it's part of SimGear and can be used in a standalone fashion if needed, ala Canvas.
  • Although independent, its aim is to be fully compatible with the current rendering framework in FG. This includes the Effects system, CameraGroup, Rembrandt and ALS (and obviously the Canvas).
  • Its functionality overlaps Rembrandt: what can be done with Rembrandt can be done with the Compositor, but not vice versa.
  • Fully configurable via an XML interface without compromising performance (ala Effects, using PropertyList files).
  • Flexible, expandable and compatible with modern graphics.
  • It doesn't increase the hardware requirements, it expands the hardware range FG can run on. People with integrated GPUs (Intel HD etc) can run a Compositor with a single pass that renders directly to the screen like before, while people with more powerful cards can run a Compositor that implements deferred rendering, for example.
  • Static branching support. Every pipeline element can be enabled/disabled at startup via a <condition> block.

How to enable the Compositor

Currently the Compositor can only be enabled at compile time via the -DENABLE_COMPOSITOR=ON CMake flag in FlightGear. SimGear doesn't require any extra parameters. Once you have a binary with the Compositor enabled and you run it, you will be presented with the default rendering pipeline. At the time of writing, this is the low spec rendering pipeline. If you want to try the ALS pipeline, start FlightGear with the command line argument: --compositor=Compositor/ALS/als

If you want to enable shadows on all objects in the ALS pipeline use these options as a startup parameters (in QT GUI or in the commandline) --prop:bool:/sim/rendering/als/shadows/enabled=true and --prop:int:/sim/rendering/als/shadows/sun-atlas-size=2048. If you feel like the shadows are too low-quality (specially in the cockpit), increase the shadow resolution to 4096 or 8192 instead of 2048.

Notes for aircraft developers

Lights

The Compositor introduces a new way of defining lights that is renderer agnostic, so every rendering pipeline will be able to access the lights that have been implemented like this. As of 2019/11, the only pipeline that supports dynamic lights is the ALS pipeline. The resulting light volumes can be visualized for debugging purposes by setting the property /sim/debug/show-light-volumes to true.

<light>
  <name>my-spotlight</name>
  <type>spot</type>
  <position>
    <x-m>-7.7476</x-m>
    <y-m>0</y-m>
    <z-m>-1.7990</z-m>
  </position>
  <direction>
    <x>-1.0</x>
    <y>0</y>
    <z>-0.013</z>
  </direction>
  <ambient>
    <r>0.03</r>
    <g>0.03</g>
    <b>0.03</b>
    <a>1</a>
  </ambient>
  <diffuse>
    <r>0.95</r>
    <g>0.9</g>
    <b>0.9</b>
    <a>1</a>
  </diffuse>
  <specular>
    <r>0.95</r>
    <g>0.9</g>
    <b>0.9</b>
    <a>1</a>
  </specular>
  <attenuation>
    <c>1.0</c>
    <l>0.09</l>
    <q>0.032</q>
  </attenuation>
  <spot-exponent>5</spot-exponent>
  <spot-cutoff>40</spot-cutoff>
  <range-m>50</range-m>
</light>
  • name. An <animation> will be able to reference the light by this name. Most animations will work as expected (rotate, translate, spin etc).
  • type. spot or point.
  • position. The position of the light source in model space and in meters.
  • direction. Only available in spot lights. It indicates the direction of the spotlight. This parameter can be specified in three different ways:
Direction vector Look-at point Rotation angles
A vector in model space that specifies the direction. Doesn't have to be normalized.
<x>-1.0</x>
<y>0</y>
<z>-0.013</z>
The spotlight will calculate its direction by looking at this position from the light position. The point is in model space and in meters.
<lookat-x-m>-8.031</lookat-x-m>
<lookat-y-m>0</lookat-y-m>
<lookat-z-m>-2</lookat-z-m>
A three angle rotation in degrees that rotates the spotlight around the three axes. A 0 degree angle in all axes makes the spotlight point downwards (negative Z).
<pitch-deg>90</pitch-deg>
<roll-deg>0</roll-deg>
<heading-deg>0</heading-deg>
  • ambient, diffuse and specular. Four-component vectors that specify the light color.
  • attenuation. Three-component vector where <c> specifies the constant factor, <l> specifies the linear factor and <q> specifies the quadratic factor. These factors are plugged into the OpenGL light attenuation formula Spotlight attenuation.png where d is the distance of the fragment to the light source. See this table for a list of attenuation values based on the range of the light.
  • range-m. Maximum range from the light source position in meters. This value will be used by the renderers to determine if a fragment is illuminated by this source. Every fragment outside this range isn't guaranteed to be affected by the light, even if the attenuation factor isn't 0 in that particular fragment.
  • cutoff. Only available in spot lights. It specifies the maximum spread angle of a light source. Only values in the range 0 90 are accepted. If the angle between the direction of the light and the direction from the light to the fragment being lighted is greater than the spot cutoff angle, it won't be lit.
  • exponent. Only available in spot lights. Higher spot exponents result in a more focused light source, regardless of the spot cutoff angle.
  • debug-color (Optional). Sets the color of the debug light volume. By default it's red.

Shadows

The shadow mapping algorithm can be customized entirely by the rendering pipeline. This means that each one will have its own requirements when it comes to shadows. Here are some general recommendations:

  • Use the <noshadow> animation to disable shadows on objects that don't need them. An example would be billboarded lights or really small cockpit elements that don't need shadows and would cause degraded performance.
  • Try to mark as many cockpit objects as possible as interior.
<model>
  <name>interior</name>
  <usage>interior</usage>
  <path>Aircraft/JA37/Models/ja37-interior.xml</path> <!-- All the objects that should only be seen when inside the cockpit are in this file -->
</model>
  • Unlike in Rembrandt, polygons facing the Sun are the ones used to generate the shadow map, so single sided surfaces and non-closed objects should be rendered correctly.

Pipelines

Low-Spec pipeline

A fixed function forward rendering pipeline mainly targeted to low spec systems. It imitates the classic forward pipeline used before multi-pass rendering was introduced by using two near/far cameras rendering directly to the screen.

Screenshot showing OSG stats of the Compositor-based low-spec rendering pipeline.

ALS

The ALS pipeline tries to bring multipass rendering to the current ALS framework, effectively combining the best from ALS and Project Rembrandt.

Cascaded shadow mapping

The main issue with shadow mapping in FlightGear is the complexity of the scene graph. Culling times can become huge if we don't carefully select which parts of the scene graph we want to render in the shadow maps. Some possible optimizations:

  • Study the minimum shadow map distance we can get without noticeable light leaking. Select an appropiate amount of cascades (more cascades = more passes over all geometry, and in general we want to keep the amount of forward passes to a minimum). We should have at least three cascades: the first just for cockpit/internal shadows, the second for the whole aircraft and the third for the rest of the scenery geometry. A fourth can be added if the transition between the second and the third is too harsh.
  • Improve the culling masks (simgear/scene/util/RenderConstants.hxx). The CASTSHADOW_BIT flag is present in almost every object in the scene graph. Turning this flag off for trees, random buildings and other geometry intensive objects improves framerates by a very considerable amount. Should the user be able to select which objects cast shadows?
  • Should the terrain cast shadows? The terrain is rarely steep enough to cast shadows. Apart from that, the terrain in FlightGear messes with automatic near/far computations for the shadow passes since the geometry is not tessellated enough. Also, the terrain LOD is not good enough to have decent cull times at far cascades.
  • Adding a "internal only" shadow flag for aircraft developers. This allows farther shadow cascades to cull complex objects that are only visible in the nearest cascades. (Very important optimization for aircrafts with complex cockpit geometry).
  • Vegetation shadows will be done by the "legacy" method currently in use. Shadow mapping on vegetation is much more expensive in terms of performance and the current algorithm does the job well enough. [5]

Post-processing

Gamma correction, night vision and other ALS filters should happen in a quad pass. The current filter_combined() should be left for post-processing that requires as much precision as possible - e.g. dithering to prevent banding). HDR is not a planned feature for now so ALS will be using rgba8 buffers for most of its features.

Real-time dynamic reflections

Rendering dynamically to a cubemap is possible. As with shadow mapping, minimizing the object count and number of forward passes is vital to get good performance in FlightGear. Rendering to six cubemap faces requires six forward passes, but we can render to a dual paraboloid map instead, reducing this number to two.

Transparency

When shadows (and multipass rendering in general) come into play, transparent objects have to be treated differently, even when we are dealing with a forward renderer. In OSG there are two ways to separate transparent surfaces:

  • Using RenderBins. After a single scene cull traversal, surfaces which belong to a special RenderBin type (DepthSortedBin) are removed or moved to another camera. This is how Rembrandt does it and it is the most backwards compatible approach since RenderBins can be changed directly inside Effects.
  • Using cull masks. Two separate traversals are done: one for opaque objects and another for translucent objects. This requires offering aircraft developers another way of tagging a surface as transparent. A trivial approach would be to add a new <animation> type called 'transparent', but that wouldn't be backwards compatible. Maybe we can add some kind of system where we can change cull masks inside Effects? Would that be too hacky or out of place?

Creating a custom rendering pipeline

Since the Compositor is completely data-driven, new rendering pipelines can be created by writing a custom XML pipeline definition. This section tries to document most of the available parameters, but the best and most up-to-date resource is the Compositor parsing code in SimGear (simgear/simgear/scene/viewer). See existing pipelines in fgdata/Compositor for practical examples on how to use these parameters.

Buffers

A buffer represents a texture or, more generically, a region of GPU memory.

Parameter Name Optional Value Default Value Description
name No string Passes will be able to address the buffer by this name
type No 1d, 2d, 2d-array, 2d-multisample, 3d, rect, cubemap Any texture type allowed by OpenGL
width No Any unsigned integer or screen to use the physical viewport width. The <property> tag can also be used to use a property value Texture width
screen-width-scale Yes float 1.0 If screen was used, this controls the width scaling factor
height No Any unsigned integer or screen to use the physical viewport height. The <property> tag can also be used to use a property value Texture height
screen-height-scale Yes float 1.0 If screen was used, this controls the height scaling factor
depth No Any unsigned integer. The <property> tag can also be used to use a property value Texture depth
format Yes See simgear/simgear/scene/viewer/CompositorBuffer.cxx for the latest available values rgba8 Specifies the texture format. It corresponds to the internalformat, format and type arguments of the OpenGL function glTexImage2D
min-filter, mag-filter Yes linear, linear-mipmap-linear, linear-mipmap-nearest, nearest, nearest-mipmap-linear, nearest-mipmap-nearest linear Change the minification and magnification filtering respectively
wrap-s, wrap-t, wrap-r Yes clamp, clamp-to-edge, clamp-to-border, repeat, mirror clamp-to-border They change the wrap mode for each coordinate
anisotropy Yes float 1.0
border-color Yes vec4 (0.0f, 0.0f, 0.0f, 0.0f)
shadow-comparison Yes bool true
shadow-texture-mode Yes luminance, intensity, alpha luminance
shadow-compare-func Yes never, less, equal, lequal, greater, notequal, gequal, always lequal

Passes

A pass wraps around an osg::Camera. Passes all have some common parameters:

Parameter Name Optional Value Default Value Description
clear-color, clear-accum, clear-depth and clear-stencil Yes vec4 black, black, 1.0, 0 respectively Pass clear colors
clear-mask Yes color, stencil, depth, accum color depth Pass clear mask
effect-scheme Yes Valid effect scheme name None The pass will try to use the specified effect scheme to draw every object.

Passes can render to a buffer (Render to Texture), to several buffers (Multiple Render Targets) or directly to the framebuffer. This is accomplished by the <attachment> tag. Possible parameters of an attachment are:

Parameter Name Optional Value Default Value Description
buffer No Valid buffer name The name of the buffer to output to
component No color, color0 to color15, depth, stencil, depth-stencil FBO attachment point
level Yes int 0 Mipmap level of the texture that is attached
face Yes int 0 Face of cube map texture or z-level of 3d texture
mipmap-generation Yes bool false Whether mipmap generation should be done for texture
multisample-samples Yes int 0 Multisample anti-aliasing (MSAA) samples
multisample-color-samples Yes int 0 Multisample anti-aliasing (MSAA) color samples

Passes can also receive buffers as input and use them in their shaders. This is accomplished by the <binding> tag, which has the following parameters:

Parameter Name Optional Value Default Value Description
buffer No Valid buffer name The name of the buffer to bind
unit No int The texture unit to place the texture on. Effects will be able to access the buffer on this texture unit

There are specific pass types, each with their own set of custom parameters.

scene

Renders the scene from the point of view given by the CameraGroup.

Parameter Name Optional Value Default Value Description
cull-mask Yes A 32 bit number. See simgear/simgear/scene/util/RenderConstants.hxx to know which bits enable what 0xffffffff Specifies the cull mask to be used in the underlying osg::Camera
z-near, z-far Yes int Default Z range in the CameraGroup They change the depth range to be used
cubemap-face Yes int -1 (don't use cubemap) Ignores the given view and projection matrices and uses a custom one that renders the scene as if it was seen from inside a cubemap looking towards the specified face

quad

Renders a fullscreen quad with an optional effect applied. Useful for screen space shaders (like SSAO, Screen Space Reflections or bloom) and deferred rendering.

Parameter Name Optional Value Default Value Description
geometry Yes float values for <x>, <y>, <width>, <height> 0.0, 0.0, 1.0, 1.0 respectively Size of the fullscreen quad inside the viewport using normalized coordinates.
effect Yes Valid Effect file None This Effect will be applied to the quad geometry

shadow-map

Renders the scene from a light's point of view.

Parameter Name Optional Value Default Value Description
light-name No Valid light name that exists in the scene graph The name of the osg::LightSource to use for this shadow map
near-m, far-m No Valid Effect file They specify the depth range of the shadow map

TODO

  • Bring back distortion correction.
  • Some kind of versioning system to be able to make breaking changes in the future if/when the compositor is updated in any significant way, without people having to manually update their configs.
  • Bring back Canvas integration so aircraft devs have access to the rendering pipeline. This allows to render exterior views in cockpit displays etc.
  • Automatically calculate light source attenuation based on radius and radius based on attenuation.
  • Add 1-bit transparency to shadow mapping (maybe even full blown transparency with multiple depth buffers?).

Known Issues

  • Setting a buffer scale factor different from 1.0 and rendering to it might not scale the splash screen correctly.
  • Clustered shading crashes FG if compiled under OSG 3.6. This is related to osg::TextureBuffer changing definition from OSG 3.4 to OSG 3.6 (Images vs BufferData).
  • Relative path Effects in aircrafts don't work. This is not permanent, they will work again once the Compositor replaces the legacy renderer.
  • EarthView doesn't work.
  • There is some kind of moiré pattern at certain sunlight angles (specially at dusk/dawn).
  • hud.eff doesn't work under the ALS pipeline.
  • Spotlights sometimes disappear at certain view angles.
  • Vegetation appears to flicker at long distances.

References

References

Related content

Wiki articles

Forum topics