我們知道，DDMS可以很容易的獲取Android 手機 的屏幕截圖，那么它是怎么做到的呢？

其實，android手機上有一個叫做FrameBuffer的設備，圖像信息都是通過FrameBuffer寫到手機屏幕上去的。因此可以通過讀取此設備中的數據來獲取當前正在顯示的圖像。當然DDMS也是這么做到的。

FrameBuffer 對應的設備文件就是/dev/graphics/fb0。因此我們可以通過下面的代碼讀取屏幕圖像數據。其中傳入的參數fd為一個文件描述符，也可以是 socket描述符。這樣我們就可以把從fb中讀取的屏幕圖像信息傳遞給我們自己的應用，從而獲取手機屏幕信息。

void framebuffer_service(int fd)
{
struct fb_var_screeninfo vinfo;
int fb, offset;
char x[256];

struct fbinfo fbinfo;
unsigned i, bytespp;

fb = open("/dev/graphics/fb0", O_RDONLY);
if(fb < 0) goto done;

if(ioctl(fb, FBIOGET_VSCREENINFO, &vinfo) < 0) goto done;
fcntl(fb, F_SETFD, FD_CLOEXEC);

bytespp = vinfo.bits_per_pixel / 8;

fbinfo.version = DDMS_RAWIMAGE_VERSION;
fbinfo.bpp = vinfo.bits_per_pixel;
fbinfo.size = vinfo.xres * vinfo.yres * bytespp;
fbinfo.width = vinfo.xres;
fbinfo.height = vinfo.yres;
fbinfo.red_offset = vinfo.red.offset;
fbinfo.red_length = vinfo.red.length;
fbinfo.green_offset = vinfo.green.offset;
fbinfo.green_length = vinfo.green.length;
fbinfo.blue_offset = vinfo.blue.offset;
fbinfo.blue_length = vinfo.blue.length;
fbinfo.alpha_offset = vinfo.transp.offset;
fbinfo.alpha_length = vinfo.transp.length;

/* 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 = vinfo.xoffset * bytespp;

offset += vinfo.xres * vinfo.yoffset * bytespp;
printf("offset %d/n", offset);

if(writex(fd, &fbinfo, sizeof(fbinfo))) goto done;

lseek(fb, offset, SEEK_SET);
for(i = 0; i < fbinfo.size; i += 256) {
if(readx(fb, &x, 256)) goto done;
if(writex(fd, &x, 256)) goto done;
}

if(readx(fb, &x, fbinfo.size % 256)) goto done;
if(writex(fd, &x, fbinfo.size % 256)) goto done;

done:
if(fb >= 0) close(fb);
close(fd);
}

編輯器加載中...

轉載于:https://www.cnblogs.com/greensoft-taobao/archive/2011/11/09/2243356.html

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