嵌入式Linux通用截图工具

为了截几张图片给idcfree的A1做宣传，昨天写了一个截图工具。这个工具与其它截图工具不同的是，它不基于任何具体的GUI，直接从framebuffer中截图，然后保存为jpeg图片，所以适用于任何嵌入式Linux设备。

o 打开framebuffer

static int fb_open(struct FB *fb, const char* fbfilename)
{
fb->fd = open(fbfilename, O_RDWR);
if (fb->fd < 0)
{
fprintf(stderr, "can't open %s\n", fbfilename);
return -1;
}

if (ioctl(fb->fd, FBIOGET_FSCREENINFO, &fb->fi) < 0)
goto fail;
if (ioctl(fb->fd, FBIOGET_VSCREENINFO, &fb->vi) < 0)
goto fail;

fb->bits = mmap(0, fb_size(fb), PROT_READ | PROT_WRITE,
MAP_SHARED, fb->fd, 0);
if (fb->bits == MAP_FAILED)
goto fail;

return 0;
fail:
printf("%s is not a framebuffer.\n", fbfilename);
close(fb->fd);

return -1;
}

o 读取数据并写入jpeg

static int snap(const char * filename, int quality, struct FB* fb)
{
int row_stride = 0;
FILE * outfile = NULL;
JSAMPROW row_pointer[1] = {0};
struct jpeg_error_mgr jerr = {0};
struct jpeg_compress_struct cinfo = {0};

cinfo.err = jpeg_std_error(&jerr);
jpeg_create_compress(&cinfo);

if ((outfile = fopen(filename, "wb+")) == NULL)
{
fprintf(stderr, "can't open %s\n", filename);

return -1;
}

jpeg_stdio_dest(&cinfo, outfile);
cinfo.image_width = fb_width(fb);
cinfo.image_height = fb_height(fb);
cinfo.input_components = 3;
cinfo.in_color_space = JCS_RGB;
jpeg_set_defaults(&cinfo);
jpeg_set_quality(&cinfo, quality, TRUE);
jpeg_start_compress(&cinfo, TRUE);

row_stride = fb_width(fb) * 2;
JSAMPLE* image_buffer = malloc(3 * fb_width(fb));

while (cinfo.next_scanline < cinfo.image_height)
{
int i = 0;
unsigned short* line = fb->bits + cinfo.next_scanline * fb_width(fb);
for(i = 0; i < fb_width(fb); i++)
{
int offset = i * 3;
unsigned short color = line[i];
unsigned char r = ((color >> 11) & 0xff) << 3;
unsigned char g = ((color >> 5) & 0xff)  << 2;
unsigned char b = (color & 0xff )<< 3;
image_buffer[offset]     = r;
image_buffer[offset + 1] = g;
image_buffer[offset + 2] = b;
}

row_pointer[0] = image_buffer;
(void) jpeg_write_scanlines(&cinfo, row_pointer, 1);
}

jpeg_finish_compress(&cinfo);
fclose(outfile);

jpeg_destroy_compress(&cinfo);

return 0;
}

o 主函数

int main(int argc, char* argv[])
{
struct FB fb = {0};
const char* filename   = NULL;
const char* fbfilename = NULL;

if(argc != 3)
{   
printf("\nusage: %s [jpeg] [framebuffer]\n", argv[0]);
printf("-----------------------------------------\n");
printf("Powered by idcfree(www.idcfree.com)\n");
return 0;
}

filename   = argv[1];
fbfilename = argv[2];
if (fb_open(&fb, fbfilename) == 0)
{
snap(filename, 100, &fb);
fb_close(&fb);
}

return 0;
}