Difference between revisions of "Compositor"

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{{forum|47|Effects & Shaders}}
 +
 
{{infobox subsystem
 
{{infobox subsystem
|image      = Canvas-view-element-prototype-by-icecode gl.png
+
|image      = ALS Compositor pipeline.jpg
|name        = Compositor Subsystem
+
|name        = Compositor Framework
|started    = 01/2018
+
|started    = 01/2018 (Available since FlightGear 2020.4)
|description = Dynamic rendering pipeline configured via the property tree
+
|description = Dynamic rendering pipeline configured via the [[Property tree]] and [[PropertyList XML File|XML]]
|status      = experimental as of 02/2018
+
|status      = Stable (merged and actively maintained)
|maintainers = none
+
|developers  = Fernando García Liñán <ref>https://sourceforge.net/u/fgarlin/profile/</ref>
|developers  = Icecode
+
|changelog = https://sourceforge.net/u/fgarlin/profile/feed.rss
 +
|folders =  
 +
* {{simgear file|simgear/scene/viewer}}
 +
* {{flightgear file|src/Viewer}}
 +
* {{fgdata file|Compositor}}
 
}}
 
}}
  
A '''Compositor''' is a rendering pipeline configured by the [[Property Tree]]. Every configurable element of the pipeline wraps an OpenGL/OSG object and exposes its parameters to the property tree. This way, the rendering pipeline becomes dynamically-reconfigurable at runtime.
+
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 [[Howto:Configure camera view windows|CameraGroup settings]]. If no Compositor file is specified for a physical camera, the one given by the <code>--compositor=</code> startup command will be used. If such startup option is not used either, FlightGear will look for a valid Compositor file in <tt>$FG_ROOT/Compositor/default.xml</tt>.
  
Related efforts: [[Howto:Canvas_View_Camera_Element]]
+
The Compositor introduces a new dedicated fgdata directory for new/custom rendering pipelines: {{Fgdata file|Compositor}}.
  
== Use Cases ==
+
== Background ==
 +
{{See also|Supporting multiple renderers|Howto:Canvas View Camera Element}}
  
== Elements ==
+
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 <ref>{{cite web
 +
  |url    = https://sourceforge.net/p/flightgear/mailman/message/28946515/
 +
  |title  = <nowiki> Re: [Flightgear-devel] [Rembrandt] the plan </nowiki>
 +
  |author = <nowiki> Mathias Fröhlich </nowiki>
 +
  |date  = Mar 7th, 2012
 +
  |added  =  Mar 7th, 2012
 +
  |script_version = 0.36
 +
  }}</ref> and at the time plans were discussed to unify this with the ongoing Rembrandt implementation (no longer maintained).
  
=== Buffers ===
+
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 <ref>{{cite web
 +
  |url    = https://sourceforge.net/p/flightgear/mailman/message/28944773/
 +
  |title  = <nowiki> Re: [Flightgear-devel] [Rembrandt] the plan </nowiki>
 +
  |author = <nowiki> Frederic Bouvier </nowiki>
 +
  |date  = Mar 7th, 2012
 +
  |added  = Mar 7th, 2012
 +
  |script_version = 0.36
 +
  }}</ref>
  
A buffer represents a texture or, more generically, a region of GPU memory. Textures can be of any type allowed by OpenGL: 1D, 2D, rectangle, 2Darray, 3D or cubemap.
+
Zan's original patches can still be found in his newcameras branches which allow the user to define the rendering pipeline in preferences.xml: {{gitorious source|proj=fg|repo=zans-flightgear|branch=newcameras|text=FlightGear}}, {{gitorious source|proj=fg|repo=zans-simgear|branch=newcameras|text=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. <ref>{{cite web
 +
  |url    =  https://sourceforge.net/p/flightgear/mailman/message/28944733/
 +
  |title  =  <nowiki> [Flightgear-devel] [Rembrandt] the plan </nowiki>
 +
  |author =  <nowiki> Lauri Peltonen </nowiki>
 +
  |date  =  Mar 7th, 2012
 +
  |added  =  Mar 7th, 2012
 +
  |script_version = 0.36
 +
  }}</ref>
  
A typical [[PropertyList XML File|property tree structure]] describing a buffer may be as follows:
+
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. <ref>{{forum link|type=search|title=Zan's Rembrandt and Canvas work|keywords=zan+rembrandt+canvas}}</ref>
  
 +
The new '''Compositor''' is an improved re-implementation of Zan's original work using not just XML, but also [[Property Tree|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, [[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.
 +
* Fully configurable via an XML interface without compromising performance (ala Effects, using [[PropertyList XML File|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 [[Conditions|<condition> block]].
 +
 +
== How to enable the Compositor ==
 +
 +
The Compositor is now the default renderer framework in FlightGear since 2020/11/17. It will be included as part of version 2020.4 onwards.
 +
 +
If you compile FlightGear from source, you can already try the Compositor. Make sure you are pulling the latest version of the 'next' branch.
 +
 +
If you want to enable shadows on all objects, use these options as startup parameters (in QT GUI or in the commandline) <code>--prop:bool:/sim/rendering/shadows/enabled=true</code> and <code>--prop:int:/sim/rendering/shadows/sun-atlas-size=2048</code>. If you feel like 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 <tt>/sim/debug/show-light-volumes</tt> to true.
 +
 +
{|cellpadding=10|
 +
|valign=top style="width: 20%;"|
 
<syntaxhighlight lang="xml">
 
<syntaxhighlight lang="xml">
      <buffer>
+
<light>
            <name>buffer-name</name>
+
  <name>my-spotlight</name>
    <type>2d</type>
+
  <type>spot</type>
    <width>512</width>
+
  <position>
    <height>512</height>
+
    <x-m>-7.7476</x-m>
    <scale-factor>1.0</scale-factor>
+
    <y-m>0</y-m>
    <internal-format>rgba8</internal-format>
+
    <z-m>-1.7990</z-m>
    <source-format>rgba</source-format>
+
  </position>
            <source-type>ubyte</source-type>
+
  <direction>
      </buffer>
+
    <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>
 
</syntaxhighlight>
 
</syntaxhighlight>
 +
|valign=top style="width: 80%;"|
 +
* <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>'''position'''</tt>. The position of the light source in model space and in meters.
 +
* <tt>'''direction'''</tt>. Only available in <tt>spot</tt> lights. It indicates the direction of the spotlight. This parameter can be specified in three different ways:
 +
{| class="wikitable" style="border: 1px solid darkgray;"
 +
! scope="col" style="width:33%;" |Direction vector
 +
! scope="col" style="width:33%;" |Look-at point
 +
! scope="col" style="width:33%;" |Rotation angles
 +
|-
 +
| style="padding: 10px" | A vector in model space that specifies the direction. Doesn't have to be normalized.
 +
<syntaxhighlight lang="xml">
 +
<x>-1.0</x>
 +
<y>0</y>
 +
<z>-0.013</z>
 +
</syntaxhighlight>
 +
| style="padding: 10px" | The spotlight will calculate its direction by looking at this position from the light position. The point is in model space and in meters.
 +
<syntaxhighlight lang="xml">
 +
<lookat-x-m>-8.031</lookat-x-m>
 +
<lookat-y-m>0</lookat-y-m>
 +
<lookat-z-m>-2</lookat-z-m>
 +
</syntaxhighlight>
 +
| style="padding: 10px" | 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).
 +
<syntaxhighlight lang="xml">
 +
<pitch-deg>90</pitch-deg>
 +
<roll-deg>0</roll-deg>
 +
<heading-deg>0</heading-deg>
 +
</syntaxhighlight>
 +
|}
 +
* <tt>'''ambient'''</tt>, <tt>'''diffuse'''</tt> and <tt>'''specular'''</tt>. Four-component vectors that specify the light color.
 +
* <tt>'''attenuation'''</tt>. Three-component vector where <code><c></code> specifies the constant factor, <code><l></code> specifies the linear factor and <code><nowiki><q></nowiki></code> specifies the quadratic factor. These factors are plugged into the OpenGL light attenuation formula [[File:Spotlight_attenuation.png]] where d is the distance of the fragment to the light source. See this [http://wiki.ogre3d.org/tiki-index.php?page=-Point+Light+Attenuation table] for a list of attenuation values based on the range of the light.
 +
* <tt>'''range-m'''</tt>. 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.
 +
* <tt>'''spot-cutoff'''</tt>. Only available in <tt>spot</tt> 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.
 +
* <tt>'''spot-exponent'''</tt>. Only available in <tt>spot</tt> lights. Higher spot exponents result in a more focused light source, regardless of the spot cutoff angle.
 +
* <tt>'''debug-color'''</tt> ('''Optional'''). Sets the color of the debug light volume. By default it's red.
 +
|}
  
=== Passes ===
+
=== Shadows ===
  
A pass wraps around an [http://public.vrac.iastate.edu/vancegroup/docs/OpenSceneGraphReferenceDocs-3.0/a00089.html osg::Camera]. As of February 2018, there are two types of passes supported:
+
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:
  
* '''scene'''. Renders a scene. The scene can be an already loaded scene graph node (terrain, aircraft etc.) or a path to a custom 3D model.
+
* Use the <code><noshadow></code> 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.
* '''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.
+
* Try to mark as many cockpit objects as possible as <tt>interior</tt>.
 +
<syntaxhighlight lang="xml">
 +
<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>
 +
</syntaxhighlight>
 +
* 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.
  
Passes can render to a buffer (Render to Texture), to several buffers (Multiple Render Targets) or directly to the OSG context. This allows chaining of multiple passes, sharing buffers between them.
+
== Porting and developing Effects/Shaders ==
  
Example XML for a ''quad'' type pass:
+
Effects can now have different implementations depending on the Compositor pipeline being used. For example, a grass Effect implemented for a high quality pipeline might have much more detail than one that targets low specification machines. Still, they both implement the "look" of grass, so they share the same Effect file (grass.eff).
  
 +
The Compositor chooses which implementation of an Effect to render based on the <tt><scheme></tt> of the techniques.
 
<syntaxhighlight lang="xml">
 
<syntaxhighlight lang="xml">
      <pass>
+
<technique n="15">
          <type>quad</type>
+
  <scheme>test-scheme</scheme>
          <name>pass-name</name>
+
  [...]
 
+
</technique>
          <effect>Effects/test.eff</effect>
+
   
+
          <output-buffer>
+
              <buffer>buffer-name</buffer>
+
              <component>color</component>
+
          </output-buffer>
+
      </pass>
+
 
</syntaxhighlight>
 
</syntaxhighlight>
  
== Canvas integration ==
+
In this case the technique will be chosen if the Compositor pipeline <tt><scene></tt> pass uses the <tt>test-scheme</tt> Effect scheme. Consequently, porting an Effect to a pipeline will require knowing which Effect schemes it uses and writing a technique for each one. The only exception to this is the Classic pipeline, which uses techniques with no scheme.
  
[[File:Canvas&Compositor test.png|thumb|A fullscreen quad with a shader that colors everything magenta is rendered to a buffer, which is displayed by a Canvas Image.]]
+
== Creating a custom rendering pipeline ==
  
Apart from serving as a debugging tool for visualizing the contents of a buffer, integrating the Compositor with [[Canvas]] allows aircraft developers to access RTT capabilities. Compositor buffers can be accessed within Canvas via a new custom Canvas Image protocol '''buffer://'''. For example, the path <code>buffer://test-compositor/test-buffer</code> displays the buffer test-buffer declared in test-compositor.
+
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.
  
<syntaxhighlight lang="nasal">
+
=== Buffers ===
var (width,height) = (612,612);
+
 
var title = 'Compositor&Canvas test';
+
A buffer represents a texture or, more generically, a region of GPU memory.
var window = canvas.Window.new([width,height],"dialog")
+
 
.set('title',title);
+
{| class="wikitable" style="text-align: center; font-size: 85%; width: auto; table-layout: fixed;
var myCanvas = window.createCanvas().set("background", canvas.style.getColor("bg_color"));
+
! scope="col" | Parameter Name
var root = myCanvas.createGroup();
+
! scope="col" | Optional
var path = "buffer://test-compositor/test-buffer";
+
! scope="col" | Value
var child = root.createChild("image")
+
! scope="col" | Default Value
    .setTranslation(50, 50)
+
! scope="col" | Description
    .setSize(512, 512)
+
|-
    .setFile(path);
+
! scope="row"| <tt>name</tt>
</syntaxhighlight>
+
| {{No}}
 +
| string
 +
|
 +
| Passes will be able to address the buffer by this name
 +
|-
 +
! scope="row"| <tt>type</tt>
 +
| {{No}}
 +
| <tt>1d, 2d, 2d-array, 2d-multisample, 3d, rect, cubemap</tt>
 +
|
 +
| Any texture type allowed by OpenGL
 +
|-
 +
! scope="row"| <tt>width</tt>
 +
| {{No}}
 +
| 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
 +
|
 +
| Texture width
 +
|-
 +
! scope="row"| <tt>screen-width-scale</tt>
 +
| {{Yes}}
 +
| float
 +
| <tt>1.0</tt>
 +
| If <tt>screen</tt> was used, this controls the width scaling factor
 +
|-
 +
! scope="row"| <tt>height</tt>
 +
| {{No}}
 +
| 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
 +
|
 +
| Texture height
 +
|-
 +
! scope="row"| <tt>screen-height-scale</tt>
 +
| {{Yes}}
 +
| float
 +
| <tt>1.0</tt>
 +
| 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 ===
 +
 
 +
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:
 +
 
 +
{| class="wikitable" style="text-align: center; font-size: 85%; width: auto; table-layout: fixed;
 +
! scope="col" | Parameter Name
 +
! scope="col" | Optional
 +
! scope="col" | Value
 +
! scope="col" | Default Value
 +
! scope="col" | Description
 +
|-
 +
! 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:
 +
 
 +
{| class="wikitable" style="text-align: center; font-size: 85%; width: auto; table-layout: fixed;
 +
! scope="col" | Parameter Name
 +
! scope="col" | Optional
 +
! scope="col" | Value
 +
! scope="col" | Default Value
 +
! scope="col" | Description
 +
|-
 +
! scope="row"| <tt>buffer</tt>
 +
| {{No}}
 +
| Valid buffer name
 +
|
 +
| The name of the buffer to output to
 +
|-
 +
! scope="row"| <tt>component</tt>
 +
| {{No}}
 +
| <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:
 +
 
 +
{| class="wikitable" style="text-align: center; font-size: 85%; width: auto; table-layout: fixed;
 +
! scope="col" | Parameter Name
 +
! scope="col" | Optional
 +
! scope="col" | Value
 +
! scope="col" | Default Value
 +
! 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.
 +
 
 +
==== scene ====
 +
Renders the scene from the point of view given by the CameraGroup.
 +
{| class="wikitable" style="text-align: center; font-size: 85%; width: auto; table-layout: fixed;
 +
! scope="col" | Parameter Name
 +
! scope="col" | Optional
 +
! scope="col" | Value
 +
! scope="col" | Default Value
 +
! scope="col" | Description
 +
|-
 +
! 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}}
 +
| float
 +
| 0.0 uses the value given by the CameraGroup
 +
| Sets a custom near and far values. Useful for implementing depth partition and limiting the depth range on cubemap passes
 +
|-
 +
! 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
 +
|-
 +
! scope="row"| <tt>use-shadow-pass</tt>
 +
| {{Yes}}
 +
| string
 +
| Empty
 +
| Name of a shadow mapping pass. Exposes shadow mapping related uniforms to the shaders of the current pass
 +
|}
 +
 
 +
Scene passes can also use the tag <code><clustered-shading></code> to enable clustered shading (lights). The following parameters are available:
 +
 
 +
{| class="wikitable" style="text-align: center; font-size: 85%; width: auto; table-layout: fixed;
 +
! scope="col" | Parameter Name
 +
! scope="col" | Optional
 +
! scope="col" | Value
 +
! scope="col" | Default Value
 +
! scope="col" | Description
 +
|-
 +
! scope="row"| <tt>tile-size</tt>
 +
| {{Yes}}
 +
| int
 +
| 128
 +
| Size of each clustered shading tile
 +
|-
 +
! scope="row"| <tt>num-threads</tt>
 +
| {{Yes}}
 +
| int
 +
| 1
 +
| Number of threads to use during the light culling process. Keep in mind that a high thread count when there aren't many lights will worsen performance due to the thread creation overhead
 +
|-
 +
! scope="row"| <tt>depth-slices</tt>
 +
| {{Yes}}
 +
| int
 +
| 1
 +
| Number of slices to partition the view frustum in the Z axis. Higher numbers will cull lights more aggressively, increasing performance if there are many lights further out that don't contribute much to the overall scene's lighting
 +
|}
 +
 
 +
==== 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.
 +
{| class="wikitable" style="text-align: center; font-size: 85%; width: auto; table-layout: fixed;
 +
! scope="col" | Parameter Name
 +
! scope="col" | Optional
 +
! 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
 +
|}
 +
 
 +
==== csm ====
 +
Implements Cascaded Shadow Mapping by rendering the scene from a light's point of view (the Sun by default). For now it only supports directional light sources. There has to be one <tt>csm</tt> pass for each cascade.
 +
{| class="wikitable" style="text-align: center; font-size: 85%; width: auto; table-layout: fixed;
 +
! scope="col" | Parameter Name
 +
! scope="col" | Optional
 +
! scope="col" | Value
 +
! scope="col" | Default Value
 +
! scope="col" | Description
 +
|-
 +
! scope="row"| <tt>light-name</tt>
 +
| {{Yes}}
 +
| Valid light name that exists in the scene graph
 +
| <tt>FGLightSource</tt> (Sun)
 +
| The name of the <tt>osg::LightSource</tt> to use for this shadow map
 +
|-
 +
! scope="row"| <tt>render-at-night</tt>
 +
| {{Yes}}
 +
| bool
 +
| true
 +
| Whether to render the shadows at night or not
 +
|-
 +
! scope="row"| <tt>near-m, far-m</tt>
 +
| {{No}}
 +
| float (meters)
 +
|
 +
| They specify the depth range of the shadow map
 +
|}
  
 
== Known Issues ==
 
== Known Issues ==
 +
See [https://sourceforge.net/p/flightgear/codetickets/search/?q=%21status%3AInvalid+%26%26+%21status%3ADuplicate+%26%26+%21status%3AFixed+%26%26+%21status%3ADone++%26%26+labels%3ACompositor open SourceForge tickets with the Compositor label].
 +
 +
== References ==
 +
{{Appendix}}
 +
 +
== Related content ==
 +
=== Wiki articles ===
 +
* [[Canvas View Camera Element]]
 +
* [[CompositeViewer Support]]
 +
* [[Uniform Buffer Objects]]
 +
* [[FlightGear CIGI Support (Common Image Generator Interface)]]
 +
 +
=== Forum topics ===
 +
* {{forum link|t=36269|text=The Compositor}}
 +
* {{forum link|t=35095|text=Clustered Forward Rendering}} (12/2018)
 +
* {{forum link|t=33045|text=Getting started with RTT}}
  
* Canvas doesn't update its texture unless .update() is invoked in Nasal. Is this a feature?
+
[[Category:Compositor]]
* The scene graph and the viewer are still managed by FGRenderer. Maybe hijacking the init sequence is a good idea?
+
* Effects need that buffers are created before reading the .eff file. Maybe some kind of listener is needed ala Rembrandt?
+

Latest revision as of 12:52, 17 November 2020

Compositor Framework
ALS Compositor pipeline.jpg
Started in 01/2018 (Available since FlightGear 2020.4)
Description Dynamic rendering pipeline configured via the Property tree and XML
Contributor(s) Fernando García Liñán [1]
Status Stable (merged and actively maintained)
Folders
Changelog https://sourceforge.net/u/fgarlin/profile/feed.rss

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 [2] 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 [3]

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. [4]

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. [5]

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

The Compositor is now the default renderer framework in FlightGear since 2020/11/17. It will be included as part of version 2020.4 onwards.

If you compile FlightGear from source, you can already try the Compositor. Make sure you are pulling the latest version of the 'next' branch.

If you want to enable shadows on all objects, use these options as startup parameters (in QT GUI or in the commandline) --prop:bool:/sim/rendering/shadows/enabled=true and --prop:int:/sim/rendering/shadows/sun-atlas-size=2048. If you feel like 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.
  • spot-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.
  • spot-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.

Porting and developing Effects/Shaders

Effects can now have different implementations depending on the Compositor pipeline being used. For example, a grass Effect implemented for a high quality pipeline might have much more detail than one that targets low specification machines. Still, they both implement the "look" of grass, so they share the same Effect file (grass.eff).

The Compositor chooses which implementation of an Effect to render based on the <scheme> of the techniques.

<technique n="15">
  <scheme>test-scheme</scheme>
  [...]
</technique>

In this case the technique will be chosen if the Compositor pipeline <scene> pass uses the test-scheme Effect scheme. Consequently, porting an Effect to a pipeline will require knowing which Effect schemes it uses and writing a technique for each one. The only exception to this is the Classic pipeline, which uses techniques with no scheme.

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 float 0.0 uses the value given by the CameraGroup Sets a custom near and far values. Useful for implementing depth partition and limiting the depth range on cubemap passes
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
use-shadow-pass Yes string Empty Name of a shadow mapping pass. Exposes shadow mapping related uniforms to the shaders of the current pass

Scene passes can also use the tag <clustered-shading> to enable clustered shading (lights). The following parameters are available:

Parameter Name Optional Value Default Value Description
tile-size Yes int 128 Size of each clustered shading tile
num-threads Yes int 1 Number of threads to use during the light culling process. Keep in mind that a high thread count when there aren't many lights will worsen performance due to the thread creation overhead
depth-slices Yes int 1 Number of slices to partition the view frustum in the Z axis. Higher numbers will cull lights more aggressively, increasing performance if there are many lights further out that don't contribute much to the overall scene's lighting

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

csm

Implements Cascaded Shadow Mapping by rendering the scene from a light's point of view (the Sun by default). For now it only supports directional light sources. There has to be one csm pass for each cascade.

Parameter Name Optional Value Default Value Description
light-name Yes Valid light name that exists in the scene graph FGLightSource (Sun) The name of the osg::LightSource to use for this shadow map
render-at-night Yes bool true Whether to render the shadows at night or not
near-m, far-m No float (meters) They specify the depth range of the shadow map

Known Issues

See open SourceForge tickets with the Compositor label.

References

References

Related content

Wiki articles

Forum topics