in API 16
The RenderScript fragment program, also known as fragment shader is responsible
for manipulating pixel data in a user defined way. It's constructed from a GLSL
shader string containing the program body, textures inputs, and a Type object
that describes the constants used by the program. Similar to the vertex programs,
when an allocation with constant input values is bound to the shader, its values
are sent to the graphics program automatically.
The values inside the allocation are not explicitly tracked. If they change between two draw
calls using the same program object, the runtime needs to be notified of that
change by calling rsgAllocationSyncAll so it could send the new values to hardware.
Communication between the vertex and fragment programs is handled internally in the
GLSL code. For example, if the fragment program is expecting a varying input called
varTex0, the GLSL code inside the program vertex must provide it.
