246 lines
9.1 KiB
Text
246 lines
9.1 KiB
Text
Effects describe the graphical appearance of 3d objects and scenery in
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FlightGear. The main motivation for effects is to support OpenGL
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shaders and to provide different implementations for graphics hardware
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of varying capabilities. Effects are similar to DirectX effects files
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and Ogre3D material scripts.
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An effect is a property list. The property list syntax is extended
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with new "vec3d" and "vec4d" types to support common computer graphics
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values. Effects are read from files with a ".eff" extension or can be
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created on-the-fly by FlightGear at runtime. An effect consists of a
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"parameters" section followed by "technique" descriptions. The
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"parameters" section is a tree of values that describe, abstractly,
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the graphical appearence of objects that use the effect. Techniques
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refer to these parameters and use them to set OpenGL state or to set
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parameters for shader programs.
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Parameters can be declared to have a dynamic variance, which means
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that if their value is changed the corresponding value in the
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technique will be changed too. [TO BE IMPLEMENTED]
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A technique can contain a predicate that describes the OpenGL
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functionality required to support the technique. The first
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technique with a valid predicate in the list of techniques is used
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to set up the graphics state of the effect. A technique with no
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predicate is always assumed to be valid. The predicate is written in a
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little expression language that supports the following primitives:
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and, or, equal, less, less-equal
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glversion - returns the version number of OpenGL
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extension-supported - returns true if an OpenGL extension is supported
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property - returns the boolean value of a property
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A technique can consist of several passes. A pass is basically an Open
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Scene Graph StateSet. Ultimately all OpenGL and OSG modes and state
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attributes will be setable in a technique. The following are
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are currently implemented:
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lighting - true, false
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shade-model - flat, smooth
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cull-face - front, back, front-back
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rendering-hint - (OSG) opaque, transparent
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render-bin - children: bin-number, bin-name
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material - children: ambient, ambient-front, ambient-back, diffuse,
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diffuse-front, diffuse-back, specular, specular-front,
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specular-back, emissive, emissive-front, emissive-back, shininess,
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shininess-front, shininess-back, color-mode
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blend - true, false
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alpha-test - true, false
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texture-unit - has several child properties:
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unit - The number of an OpenGL texture unit
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type - This is either an OpenGL texture type or the name of a
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builtin texture. Currently supported OpenGL types are 1d, 2d,
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3d which have the following common parameters:
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image (file name)
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filter
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mag-filter
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wrap-s
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wrap-t
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wrap-r
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The following builtin types are supported:
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white - 1 pixel white texture
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noise - a 3d noise texture
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environment
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mode
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color
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program
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vertex-shader
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fragment-shader
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uniform
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name
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type - float, float-vec3, float-vec4, sampler-1d, sampler-2d,
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sampler-3d
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polygon-mode
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front - fill, line, point
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back - fill, line, point
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One feature not fully illustrated in the sample below is that
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effects can inherit from each other. The parent effect is listed in
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the "inherits-from" form. The child effect's property tree is
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overlaid over that of the parent. Nodes that have the same name and
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property index -- set by the "n=" attribute in the property tag --
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are recursively merged. Leaf property nodes from the child have
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precedence. This means that effects that inherit from the example
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effect below could be very short, listing just new
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parameters and adding nothing to the techniques section;
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alternatively, a technique could be altered or customized in a
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child, listing (for example) a different shader program. Terrain
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materials work in this way: for each material type in materials.xml
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an effect is created that inherits from a single default terrain
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effect. The parameters section of the effect is filled in using the
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ambient, diffuse, specular, emissive, shininess, and transparent
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fields of the material. Seperate effects are created for each texture
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variant of a material.
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Material animations will be implemented by creating a new effect
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that inherits from one in a model, overriding the parameters that
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will be animated.
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<PropertyList>
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<effect>
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<name>city</name>
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<!-- <inherits-from>another-effect</inherits-from> -->
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<parameters>
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<material>
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<ambient type="vec4d">
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0.0 0.0 0.0 1.0
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</ambient>
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<diffuse type="vec4d">
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.5 .5 .5 1.0
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</diffuse>
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<specular type="vec4d">
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0.3 0.3 0.3 1.0
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</specular>
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<emissive type="vec4d" variance="dynamic">
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0.0 0.0 0.0 1.0
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</emissive>
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<shininess>1.2</shininess>
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</material>
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<texture n="0">
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<image>city.png</image>
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<filter>linear-mipmap-linear</filter>
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<!-- also repeat -->
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<wrap-s>clamp</wrap-s>
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<wrap-t>clamp-to-edge</wrap-t>
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<!--
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<wrap-r>clamp-to-border</wrap-r>
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-->
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<!-- float, signed-integer, integer -->
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<internal-format>normalized</internal-format>
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</texture>
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<texture n="1">
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<image>detail.png</image>
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<filter>linear-mipmap-linear</filter>
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<!-- also repeat -->
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<wrap-s>clamp</wrap-s>
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<wrap-t>clamp-to-edge</wrap-t>
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<!--
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<wrap-r>clamp-to-border</wrap-r>
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-->
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<!-- float, signed-integer, integer -->
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<internal-format>normalized</internal-format>
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</texture>
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<bump-height type="double">.05</bump-height>
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<pattern-rotation type="vec4d">0 0 1 1.5708</pattern-rotation>
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</parameters>
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<technique>
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<predicate>
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<!-- This is the general way to test for shader support -->
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<or>
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<less-equal>
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<value type="float">2.0</value>
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<glversion/>
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</less-equal>
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<and>
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<extension-supported>GL_ARB_shader_objects</extension-supported>
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<extension-supported>GL_ARB_shading_language_100</extension-supported>
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<extension-supported>GL_ARB_vertex_shader</extension-supported>
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<extension-supported>GL_ARB_fragment_shader</extension-supported>
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</and>
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</or>
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</predicate>
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<pass>
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<lighting>true</lighting>
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<material>
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<ambient><use>material/ambient</use></ambient>
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<diffuse><use>material/diffuse</use></diffuse>
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<specular><use>material/specular</use></specular>
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<shininess><use>material/shininess</use></shininess>
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</material>
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<texture-unit>
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<unit>0</unit>
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<image><use>texture[0]/image</use></image>
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<filter><use>texture[0]/filter</use></filter>
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<wrap-s><use>texture[0]/wrap-s</use></wrap-s>
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<wrap-t><use>texture[0]/wrap-t</use></wrap-t>
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<internal-format>
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<use>texture[0]/internal-format</use>
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</internal-format>
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</texture-unit>
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<texture-unit>
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<unit>1</unit>
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<image><use>texture[1]/image</use></image>
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<filter><use>texture[1]/filter</use></filter>
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<wrap-s><use>texture[1]/wrap-s</use></wrap-s>
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<wrap-t><use>texture[1]/wrap-t</use></wrap-t>
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<internal-format>
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<use>texture[1]/internal-format</use>
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</internal-format>
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</texture-unit>
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<uniform>
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<name>bumpHeight</name>
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<type>float</type>
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<use>bump-height</use>
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</uniform>
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<uniform>
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<name>patternRotation</name>
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<type>float-vec4</type>
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<use>pattern-rotation</use>
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</uniform>
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<uniform>
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<name>baseTexture</name>
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<type>sampler-2d</type>
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<value>0</value>
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</uniform>
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<uniform>
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<name>detailTexture</name>
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<type>sampler-2d</type>
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<value>1</value>
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</uniform>
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<shader-program>
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<!-- These two vertex shaders are linked together -->
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<vertex-shader>
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"Shaders/util.vert"
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</vertex-shader>
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<vertex-shader>
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"Shaders/foo.vert"
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</vertex-shader>
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<fragment-shader>
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"Shaders/foo.frag"
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</fragment-shader>
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</shader-program>
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</pass>
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</technique>
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<!-- This technique is always valid -->
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<technique>
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<pass>
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<lighting>true</lighting>
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<material>
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<ambient><use>material/ambient</use></ambient>
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<diffuse><use>material/diffuse</use></diffuse>
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<specular><use>material/specular</use></specular>
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</material>
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<texture-unit>
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<unit>0</unit>
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<image><use>texture[0]/image</use></image>
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<filter><use>texture[0]/filter</use></filter>
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<wrap-s><use>texture[0]/wrap-s</use></wrap-s>
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<wrap-t><use>texture[0]/wrap-t</use></wrap-t>
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<internal-format>
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<use>texture[0]/internal-format</use>
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</internal-format>
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</texture-unit>
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</pass>
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</technique>
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</effect>
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</PropertyList>
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