Using osg::DrawArrayLengths problem

[徐华兵]

osg-users:
Hello! When I use the core osg primitiveset, I see five derived class from it, and I don't know the osg::DrawArrayLengths ,it sounds to contain a std::vector, but unlike DrawElementsUByte(Int Short)which contain std::vector, it also have a variable member "fisrt".And how it acts.Can you give me a simple example to explain it?
Thanks!

[Robert Osfield]

Post by 徐华兵
Hello! When I use the core osg primitiveset, I see five derived class from it, and I don't know the osg::DrawArrayLengths ,it sounds to contain a std::vector, but unlike DrawElementsUByte(Int Short)which contain std::vector, it also have a variable member "fisrt".And how it acts.Can you give me a simple example to explain it?

DrawArrayLengths is simply a compact way of doing multiple
glDrawArray, the vector that DrawArrayLengths has contains the lengths
of the glDrawArray calls, the initial offset use is _first, then next
glDrawArray call uses _first + lenght of first array call.

For examples of an OSG class in action do a search through the OSG
source code, grep is your friend.

Robert.

[Alberto Luaces]

 Hello! When I use the core osg primitiveset, I see five derived class from
it, and I don't know the osg::DrawArrayLengths ,it sounds to contain a
std::vector, but unlike DrawElementsUByte(Int Short)which contain
std::vector, it also have a variable member "fisrt".And how it acts.Can you
give me a simple example to explain it? Thanks!

osg::DrawArray maps the functionality of OpenGL function glDrawArrays(). See
it at:

http://www.opengl.org/documentation/specs/man_pages/hardcopy/GL/html/gl/drawarrays.html

A good place to know how to use it is found at the osggeometry example. I
don't know osg::DrawArrayLengths, might be a minor twist from osg::DrawArray.
Reading OSG source code will clarify that.

HTH,

Alberto