android上用C语言读取fb0实现截屏，并保存为rgb565的bmp

工程源码：http://download.csdn.net/detail/victoryckl/4074654

一个增强版本源码：通过对fb0的操作，实现截屏，和送图片到fb0，支持rgb565 rgb888 xrgb8888格式的bmp和fb0

android上用C语言读取fb0实现截屏，保存为bmp图片，

支持16位(rgb565)、24位(rbg888)两种格式数据，并在android2.2和4.0模拟器上验证通过。

截屏实现主要有两个方面的工作，读取屏幕数据和生成图片。

1.读取屏幕数据

只读方式打开显存设备/dev/graphics/fb0，再通过mmap用共享方式(MAP_SHARED)映射到一片内存中，其他地方就可以直接以内存的方式读取屏幕数据了。

要注意的是，fb0的虚拟显示设备尺寸，大于实际屏幕显示设备的尺寸，mmap映射时需将安装虚拟尺寸进行映射，否则，截屏可能失败。

针对显存设备的主要代码：

/********************************************************************created:2012/02/07filename: myfb.cauthor:purpose:*********************************************************************/#ifndef WIN32//-------------------------------------------------------------------#include <stdio.h>#include <stdlib.h>#include <unistd.h>#include <fcntl.h>#include <sys/mman.h>#include <sys/stat.h>#include <sys/types.h>#include <linux/fb.h>#include <linux/kd.h>struct FB {    unsigned short *bits;    unsigned size;    int fd;    struct fb_fix_screeninfo fi;    struct fb_var_screeninfo vi;};int fb_bpp(struct FB *fb){if (fb) {return fb->vi.bits_per_pixel;}return 0;}int fb_width(struct FB *fb){if (fb) {return fb->vi.xres;}return 0;}int fb_height(struct FB *fb){if (fb) {return fb->vi.yres;}return 0;}int fb_size(struct FB *fb){if (fb) {unsigned bytespp = fb->vi.bits_per_pixel / 8;return (fb->vi.xres * fb->vi.yres * bytespp);}return 0;}int fb_virtual_size(struct FB *fb){if (fb) {unsigned bytespp = fb->vi.bits_per_pixel / 8;return (fb->vi.xres_virtual * fb->vi.yres_virtual * bytespp);}return 0;}void * fb_bits(struct FB *fb){unsigned short * bits = NULL;if (fb) {int offset, bytespp;bytespp = fb->vi.bits_per_pixel / 8;/* HACK: for several of our 3d cores a specific alignment* is required so the start of the fb may not be an integer number of lines* from the base.  As a result we are storing the additional offset in* xoffset. This is not the correct usage for xoffset, it should be added* to each line, not just once at the beginning */offset = fb->vi.xoffset * bytespp;offset += fb->vi.xres * fb->vi.yoffset * bytespp;bits = fb->bits + offset / sizeof(*fb->bits);}return bits;}void fb_update(struct FB *fb){if (fb) {fb->vi.yoffset = 1;ioctl(fb->fd, FBIOPUT_VSCREENINFO, &fb->vi);fb->vi.yoffset = 0;ioctl(fb->fd, FBIOPUT_VSCREENINFO, &fb->vi);}}static int fb_open(struct FB *fb){if (NULL == fb) {return -1;}    fb->fd = open("/dev/graphics/fb0", O_RDONLY);    if (fb->fd < 0) {printf("open(\"/dev/graphics/fb0\") failed!\n");        return -1;}    if (ioctl(fb->fd, FBIOGET_FSCREENINFO, &fb->fi) < 0) {printf("FBIOGET_FSCREENINFO failed!\n");        goto fail;}    if (ioctl(fb->fd, FBIOGET_VSCREENINFO, &fb->vi) < 0) {printf("FBIOGET_VSCREENINFO failed!\n");        goto fail;}    fb->bits = mmap(0, fb_virtual_size(fb), PROT_READ, MAP_SHARED, fb->fd, 0);    if (fb->bits == MAP_FAILED) {printf("mmap() failed!\n");        goto fail;}    return 0;fail:    close(fb->fd);    return -1;}static void fb_close(struct FB *fb){if (fb) {munmap(fb->bits, fb_virtual_size(fb));close(fb->fd);}}static struct FB g_fb;struct FB * fb_create(void){memset(&g_fb, 0, sizeof(struct FB));if (fb_open(&g_fb)) {return NULL;}return &g_fb;}void fb_destory(struct FB *fb){fb_close(fb);}//-------------------------------------------------------------------#endif//#ifndef WIN32

2.生成图片

这里生成的图片是bmp格式的，可以根据设备像素的位数自动生成16位(rgb565)、24位(rbg888)两种图片。

主要工作是要正确填充bmp的文件头信息，24位(rbg888)较简单。

16位(rgb565)复杂一点，biCompression成员的值必须是BI_BITFIELDS，原来调色板的前三个位置被三个DWORD变量占据，称为红、绿、蓝掩码，在565格式下，它们则分别为：0xF800、0x07E0、0x001F。

另外，需要主要的是windows要求文件大小必须是4的倍数，文件大小需要做下面的处理才能正确显示。

head->bfSize = head->bfOffBits + size;head->bfSize = (head->bfSize + 3) & ~3;size = head->bfSize - head->bfOffBits;

生成图片的主要代码：

/********************************************************************created:2012/02/07filename: savebmp.cauthor:purpose:*********************************************************************/#include <stdlib.h>#include <stdio.h>#include <memory.h>//-------------------------------------------------------------------/*　　位图文件的组成　　结构名称 符 号　　位图文件头 (bitmap-file header) BITMAPFILEHEADER bmfh　　位图信息头 (bitmap-information header) BITMAPINFOHEADER bmih　　彩色表　(color table) RGBQUAD aColors[]　　图象数据阵列字节 BYTE aBitmapBits[]*/typedef struct bmp_header {short twobyte;//两个字节，用来保证下面成员紧凑排列，这两个字符不能写到文件中//14Bchar bfType[2];//!文件的类型,该值必需是0x4D42，也就是字符'BM'unsigned int bfSize;//!说明文件的大小，用字节为单位unsigned int bfReserved1;//保留，必须设置为0unsigned int bfOffBits;//!说明从文件头开始到实际的图象数据之间的字节的偏移量，这里为14B+sizeof(BMPINFO)}BMPHEADER;typedef struct bmp_info{//40Bunsigned int biSize;//!BMPINFO结构所需要的字数int biWidth;//!图象的宽度，以象素为单位int biHeight;//!图象的宽度，以象素为单位,如果该值是正数，说明图像是倒向的，如果该值是负数，则是正向的unsigned short biPlanes;//!目标设备说明位面数，其值将总是被设为1unsigned short biBitCount;//!比特数/象素，其值为1、4、8、16、24、或32unsigned int biCompression;//说明图象数据压缩的类型#define BI_RGB        0L//没有压缩#define BI_RLE8       1L//每个象素8比特的RLE压缩编码，压缩格式由2字节组成（重复象素计数和颜色索引）；#define BI_RLE4       2L//每个象素4比特的RLE压缩编码，压缩格式由2字节组成#define BI_BITFIELDS  3L//每个象素的比特由指定的掩码决定。unsigned int biSizeImage;//图象的大小，以字节为单位。当用BI_RGB格式时，可设置为0int biXPelsPerMeter;//水平分辨率，用象素/米表示int biYPelsPerMeter;//垂直分辨率，用象素/米表示unsigned int biClrUsed;//位图实际使用的彩色表中的颜色索引数（设为0的话，则说明使用所有调色板项）unsigned int biClrImportant;//对图象显示有重要影响的颜色索引的数目，如果是0，表示都重要。}BMPINFO;typedef struct tagRGBQUAD {unsigned char rgbBlue;unsigned char rgbGreen;unsigned char rgbRed;unsigned char rgbReserved;} RGBQUAD;typedef struct tagBITMAPINFO {    BMPINFO    bmiHeader;    //RGBQUAD    bmiColors[1];unsigned int rgb[3];} BITMAPINFO;static int get_rgb888_header(int w, int h, BMPHEADER * head, BMPINFO * info){int size = 0;if (head && info) {size = w * h * 3;memset(head, 0, sizeof(* head));memset(info, 0, sizeof(* info));head->bfType[0] = 'B';head->bfType[1] = 'M';head->bfOffBits = 14 + sizeof(* info);head->bfSize = head->bfOffBits + size;head->bfSize = (head->bfSize + 3) & ~3;//windows要求文件大小必须是4的倍数size = head->bfSize - head->bfOffBits;info->biSize = sizeof(BMPINFO);info->biWidth = w;info->biHeight = -h;info->biPlanes = 1;info->biBitCount = 24;info->biCompression = BI_RGB;info->biSizeImage = size;printf("rgb888:%dbit,%d*%d,%d\n", info->biBitCount, w, h, head->bfSize);}return size;}static int get_rgb565_header(int w, int h, BMPHEADER * head, BITMAPINFO * info){int size = 0;if (head && info) {size = w * h * 2;memset(head, 0, sizeof(* head));memset(info, 0, sizeof(* info));head->bfType[0] = 'B';head->bfType[1] = 'M';head->bfOffBits = 14 + sizeof(* info);head->bfSize = head->bfOffBits + size;head->bfSize = (head->bfSize + 3) & ~3;size = head->bfSize - head->bfOffBits;info->bmiHeader.biSize = sizeof(info->bmiHeader);info->bmiHeader.biWidth = w;info->bmiHeader.biHeight = -h;info->bmiHeader.biPlanes = 1;info->bmiHeader.biBitCount = 16;info->bmiHeader.biCompression = BI_BITFIELDS;info->bmiHeader.biSizeImage = size;info->rgb[0] = 0xF800;info->rgb[1] = 0x07E0;info->rgb[2] = 0x001F;printf("rgb565:%dbit,%d*%d,%d\n", info->bmiHeader.biBitCount, w, h, head->bfSize);}return size;}static int save_bmp_rgb565(FILE * hfile, int w, int h, void * pdata){int success = 0;int size = 0;BMPHEADER head;BITMAPINFO info;size = get_rgb565_header(w, h, &head, &info);if (size > 0) {fwrite(head.bfType, 1, 14, hfile);fwrite(&info, 1, sizeof(info), hfile);fwrite(pdata, 1, size, hfile);success = 1;}return success;}static int save_bmp_rgb888(FILE * hfile, int w, int h, void * pdata){int success = 0;int size = 0;BMPHEADER head;BMPINFO info;size = get_rgb888_header(w, h, &head, &info);if (size > 0) {fwrite(head.bfType, 1, 14, hfile);fwrite(&info, 1, sizeof(info), hfile);fwrite(pdata, 1, size, hfile);success = 1;}return success;}int save_bmp(const char * path, int w, int h, void * pdata, int bpp){int success = 0;FILE * hfile = NULL;do {if (path == NULL || w <= 0 || h <= 0 || pdata == NULL) {printf("if (path == NULL || w <= 0 || h <= 0 || pdata == NULL)\n");break;}remove(path);hfile = fopen(path, "wb");if (hfile == NULL) {printf("open(%s) failed!\n", path);break;}switch (bpp){case 16:success = save_bmp_rgb565(hfile, w, h, pdata);break;case 24:success = save_bmp_rgb888(hfile, w, h, pdata);break;default:printf("error: not support format!\n");success = 0;break;}} while (0);if (hfile != NULL)fclose(hfile);return success;}//-------------------------------------------------------------------

3.运行方式：

cygwin下用ndk编译成可执行文件，再将生成的可执行文件push到模拟器的/data/local路径，

修改文件为可执行的，直接运行便可以截屏，图片保存到/mnt/sdcard/s.bmp。

[email protected] /cygdrive/e$ cd myprj/screenshot/jni/[email protected] /cygdrive/e/myprj/screenshot/jni$ ndk-buildCompile thumb  : savebmp <= savebmp.cCompile thumb  : savebmp <= screenshot.cStaticLibrary  : libsavebmp.aExecutable     : saveInstall        : save => libs/armeabi/save[email protected] /cygdrive/e/myprj/screenshot/jni$ adb shellerror: device offline[email protected] /cygdrive/e/myprj/screenshot/jni$ adb shell#[email protected] /cygdrive/e/myprj/screenshot/jni$ adb push ../libs/armeabi/save /data/local83 KB/s (10636 bytes in 0.125s)[email protected] /cygdrive/e/myprj/screenshot/jni$ adb shell# cd /data/localcd /data/local# chmod 777 savechmod 777 save# ./save./savergb565:16bit,800*480,768068# ls -l /mnt/sdcardls -l /mnt/sdcardd---rwxr-x system  sdcard_rw     2012-02-19 12:39 LOST.DIRd---rwxr-x system  sdcard_rw     2012-02-20 13:22 DCIM----rwxr-x system  sdcard_rw  768068 2012-02-20 13:22 s.bmp#

PS：工程源码中的VC工程主要用来调试生成图片的功能。

=====================================================================================================

目前，在增强版本中添加了32位的支持，但是没有32位的设备进行测试，已经有几位网友测试过，32位截图会出现颜色偏差和位置偏移，目前我这里还没有办法调试，所以32位截图的问题我还没有解决。

有位网友在小米手机上测试过也是有色差和错位问题，但后来直接在java中用Runtime.exec("/system/bin/screencap -p path")来截屏，还是png格式的。不是每个设备上都有screencap。

关于fb0中像素的格式可以参考

android4.0p-ics-src/system/core/adb# vi framebuffer_service.c，里面列举了五种格式，不过有些设备上可能不是下面的任何一种。

        case 1: /* RGBA_8888 */            fbinfo.bpp = 32;            fbinfo.size = w * h * 4;            fbinfo.width = w;            fbinfo.height = h;            fbinfo.red_offset = 0;            fbinfo.red_length = 8;            fbinfo.green_offset = 8;            fbinfo.green_length = 8;            fbinfo.blue_offset = 16;            fbinfo.blue_length = 8;            fbinfo.alpha_offset = 24;            fbinfo.alpha_length = 8;            break;        case 2: /* RGBX_8888 */            fbinfo.bpp = 32;            fbinfo.size = w * h * 4;            fbinfo.width = w;            fbinfo.height = h;            fbinfo.red_offset = 0;            fbinfo.red_length = 8;            fbinfo.green_offset = 8;            fbinfo.green_length = 8;            fbinfo.blue_offset = 16;            fbinfo.blue_length = 8;            fbinfo.alpha_offset = 24;            fbinfo.alpha_length = 0;            break;        case 3: /* RGB_888 */            fbinfo.bpp = 24;            fbinfo.size = w * h * 3;            fbinfo.width = w;            fbinfo.height = h;            fbinfo.red_offset = 0;            fbinfo.red_length = 8;            fbinfo.green_offset = 8;            fbinfo.green_length = 8;            fbinfo.blue_offset = 16;            fbinfo.blue_length = 8;            fbinfo.alpha_offset = 24;            fbinfo.alpha_length = 0;            break;        case 4: /* RGB_565 */            fbinfo.bpp = 16;            fbinfo.size = w * h * 2;            fbinfo.width = w;            fbinfo.height = h;            fbinfo.red_offset = 11;            fbinfo.red_length = 5;            fbinfo.green_offset = 5;            fbinfo.green_length = 6;            fbinfo.blue_offset = 0;            fbinfo.blue_length = 5;            fbinfo.alpha_offset = 0;            fbinfo.alpha_length = 0;            break;        case 5: /* BGRA_8888 */            fbinfo.bpp = 32;            fbinfo.size = w * h * 4;            fbinfo.width = w;            fbinfo.height = h;            fbinfo.red_offset = 16;            fbinfo.red_length = 8;            fbinfo.green_offset = 8;            fbinfo.green_length = 8;            fbinfo.blue_offset = 0;            fbinfo.blue_length = 8;            fbinfo.alpha_offset = 24;            fbinfo.alpha_length = 8;           break;

另外，关于截屏在android4.0的源码用有两个程序可以参考，这两个程序都可以截屏，一个是c++实现的，另一个是c的。

ics-src\frameworks\base\cmds\screencap\screencap.cpp

ics-src\frameworks\base\cmds\screenshot\screenshot.c

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