Hello,
A couple of weeks ago I was asked for a sample of an effects file that uses my
proposed changes to the property system; here it is. The syntax differs from
current property system syntax in two ways: it uses vector types for some
properties, and some properties can have a variance="dynamic" attribute that
indicates that a parameter can be animated and that graphics state that
depends on it may need to be updated.
Many people seem unconvinced by my arguments for new property types. That's
fine;
I'm still convinced that they are desirable :) One implementation reason that I
would like to treat values like colors as vectors is that the underlying OSG
type
is a vector, so if the components are individual properties that can be written
individually, the implementation choices for updating the OSG state are
unattractive:
1) Write the full vector every time a component is changed. This means
potentially 4
times the memory traffic to change a color, and leaves the values stored in OSG
in
an inconsistent state for a time.
2) Update all effects with dynamic components every frame. We have a lot of
material
animations, and their management is currently eats a lot of time in the update
phase,
so I'd like to avoid this. On the other hand, we may be updating most animations
every frame anyway.
3) Record which effects have been changed, then update their OSG state.
Complicated
bookkeeping...
If people really don't like the effects syntax, I might be willing to hold my
nose
and use the existing property implementation. I'm also not committed to having
the
effects properties be of class SGPropertyNode; they might be a subtype.
<?xml version="1.0" encoding="utf-8">
<!--
An effect consists of parameters and techniques. The "parameters"
section of an effect is a tree of values that describe, abstractly,
the graphical appearence 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. Parameters can be declared to
have a dynamic variance, which means that if their value is changed
the corresponding value in the technique will be changed too.
A technique can contain a predicate that describes the OpenGL
functionality required to support the technique. The first
technique with a valid predicate in the list of techniques is used
to set up the graphics state of the effect. A technique with no
predicate is always assumed to be valid.
A technique can consist of several passes, which are run in
sequence.
One feature not fully illustrated in the sample below is that
effects can inherit from each other. The parent effect is listed in
the "inherits-from" form. The child effect's property tree is
overlaid over that of the parent. This means that effects that
inherit from the example "default effect" below could be very
short, listing just new parameters and adding nothing to the
techniques section; alternatively, a technique could be altered or
customized in a child, listing (for example) a different shader
program. Material animations will be implemented by creating a new
effect that inherits from one in a model, overriding the parameters
that will be animated.
-->
<PropertyList>
<effect>
<name>default-effect</name>
<!-- <inherits-from>another-effect</inherits-from> -->
<parameters>
<material>
<ambient type="vec4d">
0.0 0.0 0.0 1.0
</ambient>
<diffuse type="vec4d">
.5 .5 .5 1.0
</diffuse>
<specular type="vec4d">
0.3 0.3 0.3 1.0
</specular>
<emissive type="vec4d" variance="dynamic">
0.0 0.0 0.0 1.0
</emissive>
<shininess>1.2</shininess>
</material>
<texture0>
<texture2d>
<image>city.png</image>
<filter>linear-mipmap-linear</filter>
<!-- also repeat -->
<wrap-s>clamp</wrap-s>
<wrap-t>clamp-to-edge</wrap-t>
<!--
<wrap-r>clamp-to-border</wrap-r>
-->
<!-- float, signed-integer, integer -->
<internal-format>normalized</internal-format>
</texture2d>
</texture0>
<texture1>
<texture2d>
<image>detail.png</image>
<filter>linear-mipmap-linear</filter>
<!-- also repeat -->
<wrap-s>clamp</wrap-s>
<wrap-t>clamp-to-edge</wrap-t>
<!--
<wrap-r>clamp-to-border</wrap-r>
-->
<!-- float, signed-integer, integer -->
<internal-format>normalized</internal-format>
</texture2d>
</texture1>
<bump-height type="double">.05</bump-height>
<pattern-rotation type="vec4d">0 0 1 1.5708</pattern-rotation>
</parameters>
<technique>
<predicate>
<or>
<less-equal>
<value>2.0</value>
<glversion/>
</less-equal>
<and>
<extension-supported>GL_ARB_shader_objects</extension-supported>
<extension-supported>GL_ARB_shading_language_100</extension-supported>
<extension-supported>GL_ARB_vertex_shader</extension-supported>
<extension-supported>GL_ARB_fragment_shader</extension-supported>
</and>
</or>
</predicate>
<pass>
<lighting>true</lighting>
<material>
<ambient><use>material/ambient</use></ambient>
<diffuse><use>material/diffuse</use></diffuse>
<specular><use>material/specular</use></specular>
<shininess><use>material/shininess</use></shininess>
</material>
<texture-unit>
<texture2d><use>texture0/texture2d</use></texture2d>
</texture-unit>
<texture-unit>
<texture2d><use>texture1/texture2d</use></texture2d>
</texture-unit>
<shader-program>
<uniform>
<name>bumpHeight</name>
<type>float</type>
<use>bump-height</use>
</uniform>
<uniform>
<name>patternRotation</name>
<type>vec4d</type>
<use>pattern-rotation</use>
</uniform>
<vertex-shader>
"Shaders/util.vert"
</vertex-shader>
<vertex-shader>
"Shaders/foo.vert"
</vertex-shader>
<fragment-shader>
"Shaders/foo.frag"
</fragment-shader>
</shader-program>
</pass>
</technique>
<technique>
<pass>
<lighting>true</lighting>
<material>
<ambient><use>material/ambient</use></ambient>
<diffuse><use>material/diffuse</use></diffuse>
<specular><use>material/specular</use></specular>
</material>
<texture-unit>
<texture2d><use>texture0/texture2d</use></texture2d>
</texture-unit>
</pass>
</technique>
</effect>
</PropertyList>
Tim
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