[Boost-users] Re: How to make an iterator with a stride... and more

Eli Pulsifer wrote:

Hello,

I have a situation which is probably quite common and already addressed by boost. So rather than write it my self, maybe someone can point me to the answer.

I've got a geometry class that needs to expose iterators for the underling vertex components. Example:

Class Vertex { positions_iterator PositionsBegin(); positions_iterator PositionsEnd(); normals_iterator NormalsBegin(); normals _iterator NormalsEnd(); ... }

The first problem is depending on the format of the underling vertices, the stride between the data elements will change. Is there some easy way to implement this?

I think writing my own using the boost::iterator_adapter is probably the way to go.

Sounds like you have the right idea.

Second problem is more involved.

The texture data not only has a stride but a variable number of elements. Some vertices have 2 texture coordinates, some 3, some even more.

Id love to define this iterator like this: stride_iterator< pair > tex_coord_iterator;

then create the iterator:

stride_tupel_iterator< pair >( pFirstTexCoord, texCoordStride, texCoordCount );

then use it:

stride_tupel_iterator< pair > it;

for( it = vertex.PositionBegin() ; it != vertex.PositionEnd() ; ++it) { pair coords; float_iterator iCoord;

for(iCoord = coords.first ; iCoord != coords.last ; ++iCoord) { } }

This will probably also require me to create my own highly special iterator class or is there a better way.

Isn't this just a strided iterator adapter composed with zip_iterator? -- Dave Abrahams Boost Consulting http://www.boost-consulting.com