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]
"
            "   -h: this message
"
            "   -p: save the file as a png.
"
            "   -d: specify the display id to capture, default %d.
"
            "If FILENAME ends with .png it will be saved as a png.
"
            "If FILENAME is not given, the results will be printed to stdout.
",
            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 16:
            *f = PIXEL_FORMAT_RGB_565;
            *bytespp = 2;
            break;
        case 24:
            *f = PIXEL_FORMAT_RGB_888;
            *bytespp = 3;
            break;
        case 32:
            // TODO: do better decoding of vinfo here
            *f = PIXEL_FORMAT_RGBX_8888;
            *bytespp = 4;
            break;
        default:
            return BAD_VALUE;
    }
    return NO_ERROR;
}

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

    const char* pname = argv[0];
    bool png = false;
    int32_t displayId = DEFAULT_DISPLAY_ID;
    int c;
    while ((c = getopt(argc, argv, "phd:")) != -1) {
        switch (c) {
            case 'p':
                png = true;
                break;
            case 'd':
                displayId = atoi(optarg);
                break;
            case '?':
            case 'h':
                usage(pname);
                return 1;
        }
    }
    argc -= optind;
    argv += optind;

    int fd = -1;
    if (argc == 0) {
        fd = dup(STDOUT_FILENO);
    } else if (argc == 1) {
        const char* fn = argv[0];
        fd = open(fn, O_WRONLY | O_CREAT | O_TRUNC, 0664);
        if (fd == -1) {
            fprintf(stderr, "Error opening file: %s (%s)
", fn, strerror(errno));
            return 1;
        }
        const int len = strlen(fn);
        if (len >= 4 && 0 == strcmp(fn+len-4, ".png")) {
            png = true;
        }
    }

    if (fd == -1) {
        usage(pname);
        return 1;
    }

    void const* mapbase = MAP_FAILED;
    ssize_t mapsize = -1;

    void const* base = 0;
    uint32_t w, s, h, f;
    size_t size = 0;

    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 >= 0) {
            struct fb_var_screeninfo vinfo;
            if (ioctl(fb, FBIOGET_VSCREENINFO, &vinfo) == 0) {
                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(0, mapsize, PROT_READ, MAP_PRIVATE, fb, 0);
                    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, 4);
            write(fd, &h, 4);
            write(fd, &f, 4);
            size_t Bpp = bytesPerPixel(f);
            for (size_t y=0 ; 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 0;
}

 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 16:
            *f = PIXEL_FORMAT_RGB_565;
            *bytespp = 2;
            break;
        case 24:
            *f = PIXEL_FORMAT_RGB_888;
            *bytespp = 3;
            break;
        case 32:
            // TODO: do better decoding of vinfo here
            *f = PIXEL_FORMAT_RGBX_8888;
            *bytespp = 4;
            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 
", fn);

    if (fn == NULL) {
        LOGE("=====path = %s 
 =====err: %s 
",fn, strerror(errno));
        return 1;
    }
    int fd = -1;
    fd = open(fn, O_WRONLY | O_CREAT | O_TRUNC, 0664);
    LOGI("=====after open ,fd:%d 
",fd);
    if (fd == -1) {
        LOGE("=====err: %s 
", strerror(errno));
        return 2;
    }

    void const* mapbase = MAP_FAILED;
    ssize_t mapsize = -1;

    void const* base = 0;
    uint32_t w, s, h, f;
    size_t size = 0;

    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 
", fb);
        if (fb >= 0) {
            struct fb_var_screeninfo vinfo;
            if (ioctl(fb, FBIOGET_VSCREENINFO, &vinfo) == 0) {
                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(0, mapsize, PROT_READ, MAP_PRIVATE, fb, 0);
                    if (mapbase != MAP_FAILED) {
                        base = (void const *) ((char const *) mapbase + offset);
                    }
                }
            }
            close(fb);
        }else{
            LOGE("=====fb = %d , err: %s 
",fb, strerror(errno));
            return 3;
        }
    }

    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 0;
}


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) <0 ){
        return JNI_FALSE;
    }
    return JNI_TRUE;
}



static int registerNatives(JNIEnv* env)
{
  if (!registerNativeMethods(env, "com/android/servicescreencap/ScreenCap",
                 methods, sizeof(methods) / sizeof(methods[0]))) {
    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 = -1;
    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）