shader-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:
- <predicate>
- <and>
- <property>/sim/rendering/shader-effects</property>
- <less-equal>
- <value type="float">1.0</value>
- <shader-language/>
- </less-equal>
- </and>
- </predicate>
+
<property>/sim/rendering/shader-effects</property>
+ <less-equal>
+ <value type="float">1.0</value>
+ <shader-language/>
+ </less-equal>
+ </and>
+ </predicate>
A technique can consist of several passes. A pass is basically an Open
effect. For example, effects that support transparent and opaque
geometry could have as part of a technique:
- <blend>
- <active><use>blend/active</use></active>
- <source>src-alpha</source>
- <destination>one-minus-src-alpha</destination>
- </blend>
+ <blend>
+
<active><use>blend/active</use></active>
+ <source>src-alpha</source>
+ <destination>one-minus-src-alpha</destination>
+ </blend>
So if the blend/active parameter is true blending will be activated
using 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:
- <uniform>
- <name>ColorsTex</name>
- <type>sampler-1d</type>
- <value type="int">2</value>
- </uniform>
- * The name of a property in the parameters section can be
- referenced using a "use" clause. For example, in the technique
- section:
- <material>
- <ambient><use>material/ambient</use></ambient>
- </material>
- Then, in the parameters section of the effect:
- <parameters>
- <material>
- <ambient type="vec4d">
- 0.2 .2 0.2 1.0
- </ambient>
- </material>
- </parameters>
-
- 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 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:
- <parameters>
- <chrome-light><use>/rendering/scene/chrome-light</use></chrome-light>
- </parameters>
- 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 values out 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.
+ constant. For example:
+ <uniform>
+ <name>ColorsTex</name>
+ <type>sampler-1d</type>
+ <value type="int">2</value>
+ </uniform>
+ * The name of a property in the parameters section can be
+ referenced using a "use" clause. For example, in the technique
+ section:
+ <material>
+ <ambient><use>material/ambient</use></ambient>
+ </material>
+ Then, in the parameters section of the effect:
+ <parameters>
+ <material>
+ <ambient type="vec4d">0.2 0.2 0.2 1.0</ambient>
+ </material>
+ </parameters>
+
+ 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 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:
+ <parameters>
+ <chrome-light><use>/rendering/scene/chrome-light</use></chrome-light>
+ </parameters>
+ 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 values out 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.
OpenGL Attributes
-----------------
The following attributes are currently implemented in techiques:
alpha-test - children: active, comparison, reference
- Valid values for comparision:
- never, less, equal, lequal, greater, notequal, gequal,
- always
+ Valid values for comparision:
+ never, less, equal, lequal, greater, notequal, gequal,
+ always
blend - children: active, source, destination, source-rgb,
- source-alpha, destination-rgb, destination-alpha
- Each operand can have the following 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
+ source-alpha, destination-rgb, destination-alpha
+ Each operand can have the following 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
cull-face - front, back, front-back
lighting - true, false
material - children: active, ambient, ambient-front, ambient-back, diffuse,
- diffuse-front, diffuse-back, specular, specular-front,
- specular-back, emissive, emissive-front, emissive-back, shininess,
- shininess-front, shininess-back, color-mode
+ diffuse-front, diffuse-back, specular, specular-front,
+ specular-back, emissive, emissive-front, emissive-back, shininess,
+ shininess-front, shininess-back, color-mode
polygon-mode - children: front, back
- Valid values:
- fill, line, point
+ Valid values:
+ fill, line, point
program
- vertex-shader
- fragment-shader
+ vertex-shader
+ geometry-shader
+ fragment-shader
+ attribute
+ geometry-vertices-out: integer, max number of vertices emitted by geometry shader
+ geometry-input-type - points, lines, lines-adjacency, triangles, triangles-adjacency
+ geometry-output-type - points, line-strip, triangle-strip
render-bin - (OSG) children: bin-number, bin-name
texture-unit - has several child properties:
unit - The number of an OpenGL texture unit
- type - This is either an OpenGL texture type or the name of a
- builtin texture. Currently supported OpenGL types are 1d, 2d,
- 3d which have the following common parameters:
+ type - This is either an OpenGL texture type or the name of a
+ builtin texture. Currently supported OpenGL types are 1d, 2d,
+ 3d which have the following common parameters:
image (file name)
- filter
- mag-filter
- wrap-s
- wrap-t
- wrap-r
- The following builtin types are supported:
- white - 1 pixel white texture
- noise - a 3d noise texture
- environment
- mode
- color
+ filter
+ mag-filter
+ wrap-s
+ wrap-t
+ wrap-r
+ The following built-in types are supported:
+ white - 1 pixel white texture
+ noise - a 3d noise texture
+ environment
+ mode
+ color
uniform
- name
- type - float, float-vec3, float-vec4, sampler-1d, sampler-2d,
- sampler-3d
+ name
+ type - float, float-vec3, float-vec4, sampler-1d, sampler-2d,
+ sampler-3d
vertex-program-two-side - true, false
overrides any default values that might be in the base effect's
parameters section.
+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 :
+
+ <generate>
+ <tangent type="int">6</tangent>
+ <binormal type="int">7</binormal>
+ <normal type="int">8</normal>
+ </generate>
+
+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 :
+
+ <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>
+
+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.
+
Default Effects in Terrain Materials and Models
----------------------------------------
+-----------------------------------------------
Effects for terrain work in this way: for each material type in
materials.xml an effect is created that inherits from a single default
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
+ shininess, color mode
+ * blend active, source, destination
+ * shade-model
+ * cull-face
+ * rendering-hint
+ * texture type, image, filter, wrap-s, wrap-t
Specifying Custom Effects
-------------------------
The Effects directory contains the effects definitions; look there for
examples. Effects/crop.eff is a good example of a complex effect.
+
+Application
+-----------
+
+To apply an effect to a model or part of a model use:
+
+ <effect>
+ <inherits-from>Effects/light-cone</inherits-from>
+ <object-name>Cone</object-name>
+ </effect>
+
+where <inherits-from> </inherits-from> contains the path to the effect you want to apply.
+The effect does not need the file extension.
+
+NOTE:
+
+Chrome, although now implemented as an effect, still retains the old method of application:
+
+ <animation>
+ <type>shader</type>
+ <shader>chrome</shader>
+ <texture>glass_shader.png</texture>
+ <object-name>windscreen</object-name>
+ </animation>
+
+in order to maintain backward compatibility.
+
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