基于V4L2的Webcam应用过程详解【附源码】(3)

capture_get_picture(...) 从摄像头得到一帧图片

int capture_get_picture (void *id, Picture *pic)
{
 // 获取, 转换
 Ctx *ctx = (Ctx*)id;
 v4l2_buffer buf;
 memset(&buf, 0, sizeof(buf));
 buf.type = V4L2_BUF_TYPE_VIDEO_CAPTURE;
 buf.memory = V4L2_MEMORY_MMAP;
 if (ioctl(ctx->vid, VIDIOC_DQBUF, &buf) < 0) {
  fprintf(stderr, "%s: VIDIOC_DQBUF err/n", __func__);
  return -1;
 }
// _save_pic(ctx->bufs[buf.index].start, buf.length);
// __asm("int $3");
 ctx->pic_src.data[0] = (unsigned char*)ctx->bufs[buf.index].start;
 ctx->pic_src.data[1] = ctx->pic_src.data[2] = ctx->pic_src.data[3] = 0;
 ctx->pic_src.linesize[0] = ctx->bytesperrow;
 ctx->pic_src.linesize[1] = ctx->pic_src.linesize[2] = ctx->pic_src.linesize[3] = 0;
 // sws_scale
 int rs = sws_scale(ctx->sws, ctx->pic_src.data, ctx->pic_src.linesize,
   0, ctx->rows, ctx->pic_target.data, ctx->pic_target.linesize);
 // out
 for (int i = 0; i < 4; i++) {
  pic->data[i] = ctx->pic_target.data[i];
  pic->stride[i] = ctx->pic_target.linesize[i];
 }
 // re queue buf
 if (ioctl(ctx->vid, VIDIOC_QBUF, &buf) < 0) {
  fprintf(stderr, "%s: VIDIOC_QBUF err/n", __func__);
  return -1;
 }
 return 1;
}

2.  X11 的本地回显: 采用 XShm, 效率还行

vs_open ()

XOpenDisplay()

XCreateSimpleWindow()

XCreateGC()

XMapWindow()

XShmCreateImage()

shmget()

shmat()