android后台截屏实现(2)--screencap源码修改

首先找到screencap类在Android源码中的位置，/442/frameworks/base/cmds/screencap/screencap.cpp

源码如下：

 /*
  * Copyright (C) 2010 The Android Open Source Project
  *
  * Licensed under the Apache License, Version 2.0 (the "License");
  * you may not use this file except in compliance with the License.
  * You may obtain a copy of the License at
  *
  *      http://www.apache.org/licenses/LICENSE-2.0
  *
  * Unless required by applicable law or agreed to in writing, software
  * distributed under the License is distributed on an "AS IS" BASIS,
  * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
  * See the License for the specific language governing permissions and
  * limitations under the License.
  */

 #include <errno.h>
 #include <unistd.h>
 #include <stdio.h>
 #include <fcntl.h>

 #include <linux/fb.h>
 #include <sys/ioctl.h>
 #include <sys/mman.h>

 #include <binder/ProcessState.h>

 #include <gui/SurfaceComposerClient.h>
 #include <gui/ISurfaceComposer.h>

 #include <ui/PixelFormat.h>

 #include <SkImageEncoder.h>
 #include <SkBitmap.h>
 #include <SkData.h>
 #include <SkStream.h>

 using namespace android;

 static uint32_t DEFAULT_DISPLAY_ID = ISurfaceComposer::eDisplayIdMain;

 static void usage(const char* pname)
 {
     fprintf(stderr,
             "usage: %s [-hp] [-d display-id] [FILENAME]\n"
             "   -h: this message\n"
             "   -p: save the file as a png.\n"
             "   -d: specify the display id to capture, default %d.\n"
             "If FILENAME ends with .png it will be saved as a png.\n"
             "If FILENAME is not given, the results will be printed to stdout.\n",
             pname, DEFAULT_DISPLAY_ID
     );
 }

 static SkBitmap::Config flinger2skia(PixelFormat f)
 {
     switch (f) {
         case PIXEL_FORMAT_RGB_565:
             return SkBitmap::kRGB_565_Config;
         default:
             return SkBitmap::kARGB_8888_Config;
     }
 }

 static status_t vinfoToPixelFormat(const fb_var_screeninfo& vinfo,
         uint32_t* bytespp, uint32_t* f)
 {

     switch (vinfo.bits_per_pixel) {
         case :
             *f = PIXEL_FORMAT_RGB_565;
             *bytespp = ;
             break;
         case :
             *f = PIXEL_FORMAT_RGB_888;
             *bytespp = ;
             break;
         case :
             // TODO: do better decoding of vinfo here
             *f = PIXEL_FORMAT_RGBX_8888;
             *bytespp = ;
             break;
         default:
             return BAD_VALUE;
     }
     return NO_ERROR;
 }

 int main(int argc, char** argv)
 {
     ProcessState::self()->startThreadPool();

     const char* pname = argv[];
     bool png = false;
     int32_t displayId = DEFAULT_DISPLAY_ID;
     int c;
     while ((c = getopt(argc, argv, "phd:")) != -) {
         switch (c) {
             case 'p':
                 png = true;
                 break;
             case 'd':
                 displayId = atoi(optarg);
                 break;
             case '?':
             case 'h':
                 usage(pname);
                 return ;
         }
     }
     argc -= optind;
     argv += optind;

     int fd = -;
     if (argc == ) {
         fd = dup(STDOUT_FILENO);
     } else if (argc == ) {
         const char* fn = argv[];
         fd = open(fn, O_WRONLY | O_CREAT | O_TRUNC, );
         if (fd == -) {
             fprintf(stderr, "Error opening file: %s (%s)\n", fn, strerror(errno));
             return ;
         }
         const int len = strlen(fn);
         if (len >=  &&  == strcmp(fn+len-, ".png")) {
             png = true;
         }
     }

     if (fd == -) {
         usage(pname);
         return ;
     }

     void const* mapbase = MAP_FAILED;
     ssize_t mapsize = -;

     void const* base = ;
     uint32_t w, s, h, f;
     size_t size = ;

     ScreenshotClient screenshot;
     sp<IBinder> display = SurfaceComposerClient::getBuiltInDisplay(displayId);
     if (display != NULL && screenshot.update(display) == NO_ERROR) {
         base = screenshot.getPixels();
         w = screenshot.getWidth();
         h = screenshot.getHeight();
         s = screenshot.getStride();
         f = screenshot.getFormat();
         size = screenshot.getSize();
     } else {
         const char* fbpath = "/dev/graphics/fb0";
         int fb = open(fbpath, O_RDONLY);
         if (fb >= ) {
             struct fb_var_screeninfo vinfo;
             if (ioctl(fb, FBIOGET_VSCREENINFO, &vinfo) == ) {
                 uint32_t bytespp;
                 if (vinfoToPixelFormat(vinfo, &bytespp, &f) == NO_ERROR) {
                     size_t offset = (vinfo.xoffset + vinfo.yoffset*vinfo.xres) * bytespp;
                     w = vinfo.xres;
                     h = vinfo.yres;
                     s = vinfo.xres;
                     size = w*h*bytespp;
                     mapsize = offset + size;
                     mapbase = mmap(, mapsize, PROT_READ, MAP_PRIVATE, fb, );
                     if (mapbase != MAP_FAILED) {
                         base = (void const *)((char const *)mapbase + offset);
                     }
                 }
             }
             close(fb);
         }
     }

     if (base) {
         if (png) {
             SkBitmap b;
             b.setConfig(flinger2skia(f), w, h, s*bytesPerPixel(f));
             b.setPixels((void*)base);
             SkDynamicMemoryWStream stream;
             SkImageEncoder::EncodeStream(&stream, b,
                     SkImageEncoder::kPNG_Type, SkImageEncoder::kDefaultQuality);
             SkData* streamData = stream.copyToData();
             write(fd, streamData->data(), streamData->size());
             streamData->unref();
         } else {
             write(fd, &w, );
             write(fd, &h, );
             write(fd, &f, );
             size_t Bpp = bytesPerPixel(f);
             for (size_t y= ; y<h ; y++) {
                 write(fd, base, w*Bpp);
                 base = (void *)((char *)base + s*Bpp);
             }
         }
     }
     close(fd);
     if (mapbase != MAP_FAILED) {
         munmap((void *)mapbase, mapsize);
     }
     return ;
 }

由源码可以看出，screencap的入口main方法是从命令行获取参数，通过分析后执行相应的操作。我们要想在java层调用这个类，就要把它的入口改成native方法的接口，修改后的代码如下：

 #include <jni.h>
 #include "com_android_servicescreencap_ScreenCap.h"

 #include <errno.h>
 #include <unistd.h>
 #include <stdio.h>
 #include <fcntl.h>

 #include <linux/fb.h>
 #include <sys/ioctl.h>
 #include <sys/mman.h>

 #include <binder/ProcessState.h>

 #include <gui/SurfaceComposerClient.h>
 #include <gui/ISurfaceComposer.h>

 #include <ui/PixelFormat.h>

 #include <SkImageEncoder.h>
 #include <SkBitmap.h>
 #include <SkData.h>
 #include <SkStream.h>

 #include <android/log.h>
 #define LOG_TAG "ServiceScreenCap"
 #define LOGD(...) __android_log_print(ANDROID_LOG_DEBUG, LOG_TAG, __VA_ARGS__)
 #define LOGI(...) __android_log_print(ANDROID_LOG_INFO, LOG_TAG, __VA_ARGS__)
 #define LOGE(...) __android_log_print(ANDROID_LOG_ERROR,LOG_TAG,__VA_ARGS__)

 using namespace android;

 static uint32_t DEFAULT_DISPLAY_ID = ISurfaceComposer::eDisplayIdMain;

 static status_t vinfoToPixelFormat(const fb_var_screeninfo& vinfo,
         uint32_t* bytespp, uint32_t* f)
 {

     switch (vinfo.bits_per_pixel) {
         case :
             *f = PIXEL_FORMAT_RGB_565;
             *bytespp = ;
             break;
         case :
             *f = PIXEL_FORMAT_RGB_888;
             *bytespp = ;
             break;
         case :
             // TODO: do better decoding of vinfo here
             *f = PIXEL_FORMAT_RGBX_8888;
             *bytespp = ;
             break;
         default:
             return BAD_VALUE;
     }
     return NO_ERROR;
 }

 static SkBitmap::Config flinger2skia(PixelFormat f)
 {
     switch (f) {
         case PIXEL_FORMAT_RGB_565:
             return SkBitmap::kRGB_565_Config;
         default:
             return SkBitmap::kARGB_8888_Config;
     }
 }

 /*
  * Class:     com_android_servicescreencap_ScreenCap
  * Method:    currentscreen
  * Signature: (Ljava/lang/String;)I
  */
 JNIEXPORT jint
 JNICALL ScreenCap_currentscreen(JNIEnv *env,
         jclass clazz, jstring jpath) {

     ProcessState::self()->startThreadPool();

     int32_t displayId = DEFAULT_DISPLAY_ID;

     const char* fn = env->GetStringUTFChars(jpath,NULL);
     LOGI("=====jpath:%s \n", fn);

     if (fn == NULL) {
         LOGE("=====path = %s \n =====err: %s \n",fn, strerror(errno));
         return ;
     }
     int fd = -;
     fd = open(fn, O_WRONLY | O_CREAT | O_TRUNC, );
     LOGI("=====after open ,fd:%d \n",fd);
     if (fd == -) {
         LOGE("=====err: %s \n", strerror(errno));
         return ;
     }

     void const* mapbase = MAP_FAILED;
     ssize_t mapsize = -;

     void const* base = ;
     uint32_t w, s, h, f;
     size_t size = ;

     ScreenshotClient screenshot;
     sp < IBinder > display = SurfaceComposerClient::getBuiltInDisplay(displayId);
     if (display != NULL && screenshot.update(display) == NO_ERROR) {
         base = screenshot.getPixels();
         w = screenshot.getWidth();
         h = screenshot.getHeight();
         s = screenshot.getStride();
         f = screenshot.getFormat();
         size = screenshot.getSize();
     } else {
         const char* fbpath = "/dev/graphics/fb0";
         int fb = open(fbpath, O_RDONLY);
         LOGI("=====read framebuffer, fb:%d \n", fb);
         if (fb >= ) {
             struct fb_var_screeninfo vinfo;
             if (ioctl(fb, FBIOGET_VSCREENINFO, &vinfo) == ) {
                 uint32_t bytespp;
                 if (vinfoToPixelFormat(vinfo, &bytespp, &f) == NO_ERROR) {
                     size_t offset = (vinfo.xoffset + vinfo.yoffset * vinfo.xres)
                             * bytespp;
                     w = vinfo.xres;
                     h = vinfo.yres;
                     s = vinfo.xres;
                     size = w * h * bytespp;
                     mapsize = offset + size;
                     mapbase = mmap(, mapsize, PROT_READ, MAP_PRIVATE, fb, );
                     if (mapbase != MAP_FAILED) {
                         base = (void const *) ((char const *) mapbase + offset);
                     }
                 }
             }
             close(fb);
         }else{
             LOGE("=====fb = %d , err: %s \n",fb, strerror(errno));
             return ;
         }
     }

     if (base) {
         SkBitmap b;
         b.setConfig(flinger2skia(f), w, h, s * bytesPerPixel(f));
         b.setPixels((void*) base);
         SkDynamicMemoryWStream stream;
         SkImageEncoder::EncodeStream(&stream, b, SkImageEncoder::kPNG_Type,
                 SkImageEncoder::kDefaultQuality);
         SkData* streamData = stream.copyToData();
         write(fd, streamData->data(), streamData->size());
         streamData->unref();
     }
     close (fd);
     if (mapbase != MAP_FAILED) {
         munmap((void *) mapbase, mapsize);
     }
     return ;
 }

 static JNINativeMethod methods[] = {
         {"currentscreen","(Ljava/lang/String;)I",(void*)ScreenCap_currentscreen},
 };

 static int registerNativeMethods(JNIEnv* env,const char* classname,JNINativeMethod* gMethods,int numMethods ){
     jclass clazz;
     clazz = env->FindClass(classname);
     if(clazz == NULL){
         return JNI_FALSE;
     }
     if(env->RegisterNatives(clazz,gMethods,numMethods) < ){
         return JNI_FALSE;
     }
     return JNI_TRUE;
 }

 static int registerNatives(JNIEnv* env)
 {
   if (!registerNativeMethods(env, "com/android/servicescreencap/ScreenCap",
                  methods, sizeof(methods) / sizeof(methods[]))) {
     return JNI_FALSE;
   }

   return JNI_TRUE;
 }

 typedef union {
     JNIEnv* env;
     void* venv;
 } UnionJNIEnvToVoid;

 jint JNI_OnLoad(JavaVM* vm, void* reserved)
 {
     UnionJNIEnvToVoid uenv;
     uenv.venv = NULL;
     jint result = -;
     JNIEnv* env = NULL;

     if (vm->GetEnv(&uenv.venv, JNI_VERSION_1_6) != JNI_OK) {
          return result;
     }
     env = uenv.env;

     if (registerNatives(env) != JNI_TRUE) {
          return result;
     }

     result = JNI_VERSION_1_6;

     return result;
 }

修改后的代码入口是ScreenCap_currentscreen，该方法接收一个地址，将当前屏幕截取到该地址下。代码中加入了日志，可以打印native层的错误信息。

此处需采用动态方式注册本地方法，静态方式好像会有问题。

参考链接：

Android: How to Capture Screen in Gingerbread(2.3中实现截屏)

Android: How to Capture Screen in Gingerbread(2.3中实现截屏)(续)

Android系统截屏的实现（附代码）