#### Vertex texture fetching in vertex programs

If your vertex program makes use of Vertex Texture Fetch, you should declare that with the ’uses_vertex_texture_fetch’ directive. This is enough to tell Ogre that your program uses this feature and that hardware support for it should be checked.

    	uses_vertex_texture_fetch true

#### Adjacency information in Geometry Programs

Some geometry programs require adjacency information from the geometry. It means that a geometry shader doesn’t only get the information of the primitive it operates on, it also has access to its neighbours (in the case of lines or triangles). This directive will tell Ogre to send the information to the geometry shader.

    	uses_adjacency_information true

#### Vertex Programs With Shadows

When using shadows (See Shadows), the use of vertex programs can add some additional complexities, because Ogre can only automatically deal with everything when using the fixed-function pipeline. If you use vertex programs, and you are also using shadows, you may need to make some adjustments.

If you use stencil shadows, then any vertex programs which do vertex deformation can be a problem, because stencil shadows are calculated on the CPU, which does not have access to the modified vertices. If the vertex program is doing standard skeletal animation, this is ok (see section above) because Ogre knows how to replicate the effect in software, but any other vertex deformation cannot be replicated, and you will either have to accept that the shadow will not reflect this deformation, or you should turn off shadows for that object.

If you use texture shadows, then vertex deformation is acceptable; however, when rendering the object into a shadow texture (the shadow caster pass), the shadow has to be rendered in a solid colour (linked to the ambient colour for modulative shadows, black for additive shadows). You must therefore provide an alternative vertex program, so Ogre provides you with a way of specifying one to use when rendering the caster, See Shadows and Vertex Programs.