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Effect Framework

10,173 bytes added, 02:25, 8 September 2019
Uniforms passed to shaders outside the xml effect framework: Some new info from Icecode
{{forum|47|Effects & Shaders}}
{{Rendering}}
The effect framework as per version 2019.1
 
Effects describe the graphical appearance of 3d objects and scenery in
FlightGear. The main motivation for effects is to support OpenGL
shaders and to provide different implementations for graphics hardware
of varying capabilities. Effects are similar to DirectX effects files
and Ogre3D material scripts.
 
An effect is a property list. The property list syntax is extended
with new "vec3d" and "vec4d" types to support common computer graphics
values. Effects are read from files with a ".eff" extension or can be
created on-the-fly by FlightGear at runtime. An effect consists of a
"parameters" section followed by "technique" descriptions. The
"parameters" section is a tree of values that describe, abstractly,
the graphical characteristics of objects that use the effect. Techniques
refer to these parameters and use them to set OpenGL state or to set
parameters for shader programs. The names of properties in the
parameter section can be whatever the effects author chooses, although
some standard parameters are set by FlightGear itself. On the other
hand, the properties in the techniques section are all defined by the
FlightGear.
=Default Effects in Terrain Materials and Models=
system. The parameters created are:
* material active, ambient, diffuse, specular, emissive, shininess, color mode * # blend active, source, destination * # shade-model * # cull-face * rendering-hint * texture type, image, filter, wrap-s, wrap-t
=Specifying Custom Effects=
In the terrain materials.xml, an "effect" property specifies the name
of the model to use.
 
In model .xml files, A richer syntax is supported. [TO BE DETERMINED]
Material animations will be implemented by creating a new effect
=Examples=
The $FGDATA/Effects directory contains the effects definitions; look there for
examples. Effects/crop.eff is a good example of a complex effect.
Note that parameters can use the <use> tags to enable properties to specify the values.
 
==Generate==
 
Often shader effects need tangent vectors to work properly. These
tangent vectors, usually called tangent and binormal, are computed
on the CPU and given to the shader as vertex attributes. These
vectors are computed on demand on the geometry using the effect if
the 'generate' clause is present in the effect file. Exemple :
 
<syntaxhighlight lang="xml">
<generate>
<tangent type="int">6</tangent>
<binormal type="int">7</binormal>
<normal type="int">8</normal>
</generate>
</syntaxhighlight>
 
Valid subnodes of 'generate' are 'tangent', 'binormal' or 'normal'.
The integer value of these subnode is the index of the attribute
that will hold the value of the vec3 vector.
 
The generate clause is located under PropertyList in the xml file.
 
In order to be available for the vertex shader, these data should
be bound to an attribute in the program clause, like this :
 
<syntaxhighlight lang="xml">
<program>
<vertex-shader>my_vertex_shader</vertex-shader>
<attribute>
<name>my_tangent_attribute</name>
<index>6</index>
</attribute>
<attribute>
<name>my_binormal_attribute</name>
<index>7</index>
</attribute>
</program>
</syntaxhighlight>
 
attribute names are whatever the shader use. The index is the one
declared in the 'generate' clause. So because generate/tangent has
value 6 and my_tangent_attribute has index 6, my_tangent_attribute
holds the tangent value for the vertex.
==Technique==
===predicate===
Condition for this A technique can contain a predicate that describes the OpenGLfunctionality required to be support the technique. The firsttechnique with a valid predicate in the list of techniques is usedto set up the graphics state of the effect. If this fails it will try A technique with nopredicate is always assumed to be valid. The predicate is written in alittle expression language that supports the next following primitives: and, or, equal, less, less-equalglversion - returns the version number of OpenGLextension-supported - returns true if an OpenGL extension is supportedproperty - returns the boolean value of a propertyfloat-property - returns the float value of a property, useful inside equal, less or less-equal nodesshader-language - returns the version of GLSL supported, or 0 if there is none. The proper way to test whether to enable a shader-based technique is:<syntaxhighlight lang="xml"> <predicate> <and> <property>/sim/rendering/shader-effects</property> <less-equal> <value type="float">1.0</value> <shader-language/> </less-equal> </and> </predicate></syntaxhighlight> There is also a property set by the user to indicate what is the level of quality desired. This level of quality can be checked in the effectpredicatelike this :<syntaxhighlight lang="xml"> <predicate> <and> <property>/sim/rendering/shader-effects</property> <less-equal> <value type="float">2.0</value> <float-property>/sim/rendering/quality-level</float-property> </less-equal> <!-- other predicate conditions --> </and> </predicate></syntaxhighlight> The range of /sim/rendering/quality-level is [0..5] * 2.0 is the threshold for relief mapping effects, * 4.0 is the threshold for geometry shader usage.
Example:
<syntaxhighlight lang="xml">
<predicate>
<and>
</and>
</predicate>
</syntaxhighlight>
===pass===
What A technique can consist of several passes. A pass is passed to the shaders/basically an OpenScene Graph StateSet. Ultimately all OpenGL and OSGmodes and stateattributes will be accessable in techniques.State attributes -- that(Not sureis, but think multiple passes technique properties that have children and are possiblenot just booleanmodes -- have an <active> parameter which enables or disables theattribute.)In this way a technique can declare parameters it needs,but not enable the attribute at all if it is not needed; the decisioncan be based on a parameter in the parameters section of theeffect. For example, effects that support transparent and opaquegeometry could have as part of a technique:
Note that entries <syntaxhighlight lang="xml"> <blend> <active><use>blend/active</use></active> <source>src-alpha</source> <destination>one-minus-src-alpha</destination> </blend></syntaxhighlight> So if the blend/active parameter is true blending will be activatedusing the usual blending equation; otherwise blending is disabled. Values are assigned to technique properties in several ways:  * They can appear directly in the techniques section as a constant. For example:<syntaxhighlight lang="xml"> <uniform> <name>ColorsTex</name> <type>sampler-1d</type> <value type="int">2</value> </uniform></syntaxhighlight> * The name of a property in the parameters section can be referenced using a "use " clause. For example, in the technique section:<syntaxhighlight lang="xml"> <material> <ambient><use> tags to enable material/ambient</use></ambient> </material></syntaxhighlight> Then, in the parameters section of the effect:<syntaxhighlight lang="xml"> <parameters> <material> <ambient type="vec4d">0.2 0.2 0.2 1.0</ambient> </material> </parameters></syntaxhighlight> It's worth pointing out that the "material" property in a technique specifies part of OpenGL's state, whereas "material" in the parameters section is just a name, part of a hierarchical namespace.  * A property in the parameters section doesn't need to specify contain a constant value; it can also contain a "use" property. Here the value of the use clause is the name of a node in an external property tree which will be used as the source of a value. If the name begins with '/', the node is in FlightGear's global property tree; otherwise, it is in a local property tree, usually belonging to a model [NOT IMPLEMENTED YET]. For example:<syntaxhighlight lang="xml"> <parameters> <chrome-light><use>/rendering/scene/chrome-light</use></chrome-light> </parameters></syntaxhighlight> The type is determined by what is expected by the technique attribute that will ultimately receive the value. [There is no way to get vector valuesout of the main property system yet; this will be fixed shortly.] Values that are declared this way are dynamically updated if the property node changes.
====lighting====
Children values: dst-alpha, dst-color, one, one-minus-dst-alpha, one-minus-dst-color, one-minus-src-alpha, one-minus-src-color, src-alpha, src-alpha-saturate, src-color, constant-color, one-minus-constant-color, constant-alpha, one-minus-constant-alpha, zero
 
Example:
<syntaxhighlight lang="xml">
<blend>
<active>true</active>
<source>one-minus-dst-alpha</source>
<destination>src-alpha-saturate</destination>
</blend>
</syntaxhighlight>
====shade-model====
====cull-face====
front, back, front-back, off
 
====rendering-hint====
Sent to OSG.
 
default, opaque, transparent
====texture-unit====
Example:
 
<syntaxhighlight lang="xml">
<texture-unit>
<unit>3</unit>
<image>Textures/Terrain/void.png</image>
<type>2d</type>
<filter>linear-mipmap-linear</filter>
<mag-filter>linear-mipmap-linear</mag-filter>
<wrap-s>repeat</wrap-s>
<wrap-t>repeat</wrap-t>
<wrap-r>repeat</wrap-r>
<internal-format>normalized</internal-format>
<mipmap-control>
<function-r>average</function-r>
<function-g>min</function-g>
<function-b>sum</function-b>
<function-a>product</function-a>
</mitmap-control>
<environment>
<mode>decal</mode>
<color>0.0 0.1 0.6 1.0</color>
</environment>
<point-sprite>true</point-sprite>
<texenv-combine>operand0-rgb</texenv-combine>
<texgen>
<mode>S</mode>
<planes>0.075, 0.0, 0.0, 0.5</planes>
</texgen>
</texture-unit>
</syntaxhighlight>
====vertex-program-two-side====
true or false
 
====polygon-mode====
children: front, back
 
Valid values: fill, line, point
====vertex-program-point-size====
====uniform====
Data accessible by shaders.
=====name=====
=====type=====name: the name type: bool, int, float, float-vec3, float-vec4, sampler-1d, sampler-2d, sampler-3d, sampler-1d-shadow, sampler-2d-shadow, sampler-cube
====alpha-test====
=====active=====: true, false
=====comparison=====: never, less, equal, lequal, greater, notequal, gequal, always
=====reference=====?: 0 to 1
====render-bin====
Sent to OSG.
=====bin-number=====
bin-number: This is an integer defining the order stuff will be rendered in, it can be negative also. bin-name: RenderBin, DepthSortedBin =====binrendering-namehint====Sent to OSG. default, opaque, transparent This basically just sets Renderbin: opaque =bin 10, depthsortedbinRenderBintransparent = bin 0, DepthSortedBinrenderbin default = inherit renderbin details from parent node
====program====
* geometry-output-type - points, line-strip, triangle-strip
===Generate=== Often shader effects need tangent vectors to work properly. These tangent vectors, usually called tangent and binormal, are computed on the CPU and given to the shader as vertex attributes. These vectors are computed on demand on the geometry using the effect if the 'generate' clause is present in the effect file. Exemple example:
<syntaxhighlight lang="xml">
<generateprogram> <tangent typevertex-shader n="int0">6Shaders/lcd.vert</tangentvertex-shader> <binormal typefragment-shader n="int0">7Shaders/lcd.frag</binormalfragment-shader> <normal typefragment-shader n="int1">8Shaders/noise.frag</fragment-shader> <fragment-shader n="2">Shaders/filters-ALS.frag</normalfragment-shader> </generateprogram>
</syntaxhighlight>
Valid subnodes of 'generate' are 'tangent', 'binormal' or 'normal'.The integer value of these subnode is the index of the attribute that will hold the value of the vec3 vector. The generate clause is located under PropertyList in the xml file. In order to be available See this page for the vertex shader, these data should be bound to an attribute in the program clause, like this more about shaders<syntaxhighlight lang="xml"> <program> <vertex-shader>my_vertex_shader</vertex-shader> <attribute> <name>my_tangent_attribute</name> <index>6</index> </attribute> <attribute> <name>my_binormal_attribute</name> <index>7</index> </attribute> </program></syntaxhighlight> attribute names are whatever the shader use. The index is the one declared [[Howto:Shader programming in the 'generate' clause. So because generate/tangent has value 6 and my_tangent_attribute has index 6, my_tangent_attribute holds the tangent value for the vertex.FlightGear]]
=Uniforms passed to shaders outside the xml effect framework=
mat4 osg_ViewMatrixInverse
 
mat4 osg_ViewMatrix
 
vec2 fg_BufferSize
{| class="wikitable"!Name!Type!Purpose|-|<tt>fg_ViewMatrix</tt>|<tt>mat4</tt>|In fullscreen pass only, view matrix used to transform from world to view space. Same as osg_ViewMatrix, but for fullscreen pass.|-|<tt>fg_ViewMatrixInverse</tt>|<tt>mat4</tt>|In fullscreen pass only, view matrix inverse used to transform from view to world space. Same as osg_ViewMatrixInverse but for fullscreen pass.|-|<tt>fg_ProjectionMatrixInverse</tt>|<tt>mat4</tt>|In fullscreen pass only, projection matrix inverse|-|<tt>fg_CameraPositionCart</tt>|<tt>vec3</tt>|Position of the camera in world space, expressed in cartesian coordinates|-|<tt>fg_CameraPositionGeod</tt>|<tt>vec3</tt>|Position of the camera in world space, expressed in geodesic coordinates (longitude in radians, latitude in radians, elevation in meters)|-|<tt>fg_SunAmbientColor</tt>|<tt>vec4</tt>|For fullscreen pass only, sun information as lightsource[0] is not available in fullscreen pass.|-|<tt>fg_SunDiffuseColor</tt>|<tt>vec4</tt>|For fullscreen pass only, sun information as lightsource[0] is not available in fullscreen pass.|-|<tt>fg_SunSpecularColor</tt>|<tt>vec4</tt>|For fullscreen pass only, sun information as lightsource[0] is not available in fullscreen pass.|-|<tt>fg_SunDirection</tt>|<tt>vec3</tt>|For fullscreen pass only, sun information as lightsource[0] is not available in fullscreen pass.|-|<tt>fg_FogColor</tt>|<tt>vec4</tt>||-|<tt>fg_FogDensity</tt>|<tt>float </tt>||-|<tt>fg_ShadowNumber</tt>|<tt>int</tt>||-|<tt>fg_ShadowDistances</tt>|<tt>vec4</tt>||-|<tt>fg_DepthInColor</tt>|<tt>bool</tt>|Tells if the depth is stored in a depth texture or a color texture|-|<tt>fg_Planes</tt>|<tt>vec3</tt>|Used to convert the value of the depth buffer to a depth that can be used to compute the eye space position of the fragment|-|<tt>fg_BufferSize</tt>|<tt>vec2</tt>|Dimensions of the buffer, used to convert gl_FragCoord into the range [0..1][0..1]|-|<tt>osg_ViewMatrix</tt>|<tt>mat4</tt>|Defined by OSG, used only when working on actual geometry. Transforms from world to view space.|-|<tt>osg_ViewMatrixInverse</tt>|<tt>mat4</tt>|Defined by OSG, used only when working on actual geometry. Transforms from view to world space.|-|<tt>osg_SimulationTime</tt>|<tt>float</tt>|Defined by OSG|-|<tt>osg_FrameTime</tt>|<tt>float</tt>|Defined by OSG|-|<tt>osg_DeltaFrameTime</tt>|<tt>float</tt>|Defined by OSG|-|<tt>osg_FrameTime</tt>|<tt>float</tt>|Defined by OSG|-|<tt>osg_FrameNumber</tt>|<tt>int</tt>|Defined by OSG|}
[[Category:Shader development]]
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