" The code below is to show how a heirarchy of objects can be made within a scenegraph.
In other words, how there can be a parent/child relationship between objects such
that when a parent is rotated or translated, the children move is respect to it's
parent movement. A robotic arm is used in this example because this is what I'm
using OSG for."
I have found some errors on the example osgGeometryShaders. It's about the varying in the geometry shader.
take a look at the varying vec4 v_color.
In the vertex shader, v_color is initialized to gl_vertex
then in the geometry shader v_color is initialized to gl_PositionIn[0]
and in the fragment shader v_color is used as the fragment color.
Try to initialized v_color to vec4(1.0, 0.0, 0.0, 1.0) in the vertex shader and comment the line :
" v_color = v;\n" in the geometry shader, and you will see the lines as black !
It's because you have to use keywords in and out.
extract from : http://www.opengl.org/registry/specs/EXT/geometry_shader4.txt :
in - for function parameters passed into a function or for input varying
variables (geometry only)
out - for function parameters passed back out of a function, but not
initialized for use when passed in. Also for output varying variables
(geometry only).
Then for a geometry shader, a varying must be an array :
extract from : http://www.opengl.org/registry/specs/EXT/geometry_shader4.txt :
Since a geometry shader operates on primitives, each input varying variable needs to be
declared as an array. Each element of such an array corresponds to a
vertex of the primitive being processed. If the varying variable is
declared as a scalar or matrix in the vertex shader, it will be a
one-dimensional array in the geometry shader. Each array can optionally
have a size declared. If a size is not specified, it inferred by the
linker and depends on the value of the input primitive type.
Here is a patch based on the svn version of osg that correct that.
"
set.
The optimization is based on the observation that matrix matrix multiplication
with a dense matrix 4x4 is 4^3 Operations whereas multiplication with a
transform, or scale matrix is only 4^2 operations. Which is a gain of a
*FACTOR*4* for these special cases.
The change implements these special cases, provides a unit test for these
implementation and converts uses of the expensiver dense matrix matrix
routine with the specialized versions.
Depending on the transform nodes in the scenegraph this change gives a
noticable improovement.
For example the osgforest code using the MatrixTransform is about 20% slower
than the same codepath using the PositionAttitudeTransform instead of the
MatrixTransform with this patch applied.
If I remember right, the sse type optimizations did *not* provide a factor 4
improovement. Also these changes are totally independent of any cpu or
instruction set architecture. So I would prefer to have this current kind of
change instead of some hand coded and cpu dependent assembly stuff. If we
need that hand tuned stuff, these can go on top of this changes which must
provide than hand optimized additional variants for the specialized versions
to give a even better result in the end.
An other change included here is a change to rotation matrix from quaterion
code. There is a sqrt call which couold be optimized away. Since we divide in
effect by sqrt(length)*sqrt(length) which is just length ...
"
