Android NDK Beginner's Guide - Second Edition

Time for action – processing pictures with the Bitmap API

Let's continue our application by decoding and filtering images on the native side by the color channel:

1. Create native C source, jni/CameraDecoder.c (not a C++ file, so that we can see the difference with JNI code written in C++).

   Include android/bitmap.h, which defines the NDK bitmap processing API and stdlib.h (not cstdlib as this file is written in C):

   #include <android/bitmap.h>
   #include <stdlib.h>
   ...

   Write a few utility macros to help decode a video.

   • toInt() converts a jbyte to an integer, erasing all useless bits with a mask
   • max() gets the maximum between two values
   • clamp() clamps a value inside a defined interval
   • color() builds an ARGB color from each color component

     ... #define toInt(pValue) ...