refactored calctexture.c --now using the 'JNI-interface on top of the C-interface' method
went through the calctexture function with Jason...now compiles. Most important trick was the required type: C unsigned char = Java byte
some more changes to calctexture
minor changes to JNIMethodsVol2Bird.java
enabled the texture interface in vol2bird.h
added unit test for native method calcTexture