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* @example camera.c
* Question: I need to display a live camera image via VNC. Until now I just
* grab an image, set the rect to modified and do a 0.1 s sleep to give the
* system time to transfer the data.
* This is obviously a solution which doesn't scale very well to different
* connection speeds/cpu horsepowers, so I wonder if there is a way for the
* server application to determine if the updates have been sent. This would
* cause the live image update rate to always be the maximum the connection
* supports while avoiding excessive loads.
* Thanks in advance,
* Christian Daschill
* Answer: Originally, I thought about using separate threads and using a
* mutex to determine when the frame buffer was being accessed by any client
* so we could determine a safe time to take a picture. The probem is, we
* are lock-stepping everything with framebuffer access. Why not be a
* single-thread application and in-between rfbProcessEvents perform a
* camera snapshot. And this is what I do here. It guarantees that the
* clients have been serviced before taking another picture.
* The downside to this approach is that the more clients you have, there is
* less time available for you to service the camera equating to reduced
* frame rate. (or, your clients are on really slow links). Increasing your
* systems ethernet transmit queues may help improve the overall performance
* as the libvncserver should not stall on transmitting to any single
* client.
* Another solution would be to provide a separate framebuffer for each
* client and use mutexes to determine if any particular client is ready for
* a snapshot. This way, your not updating a framebuffer for a slow client
* while it is being transferred.
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <rfb/rfb.h>
#define WIDTH 640
#define HEIGHT 480
#define BPP 4
/* 15 frames per second (if we can) */
#define PICTURE_TIMEOUT (1.0/15.0)
* throttle camera updates
int TimeToTakePicture() {
static struct timeval now={0,0}, then={0,0};
double elapsed, dnow, dthen;
dnow = now.tv_sec + (now.tv_usec /1000000.0);
dthen = then.tv_sec + (then.tv_usec/1000000.0);
elapsed = dnow - dthen;
if (elapsed > PICTURE_TIMEOUT)
memcpy((char *)&then, (char *)&now, sizeof(struct timeval));
return elapsed > PICTURE_TIMEOUT;
* simulate grabbing a picture from some device
int TakePicture(unsigned char *buffer)
static int last_line=0, fps=0, fcount=0;
int line=0;
int i,j;
struct timeval now;
* simulate grabbing data from a device by updating the entire framebuffer
for(j=0;j<HEIGHT;++j) {
for(i=0;i<WIDTH;++i) {
buffer[(j*WIDTH+i)*BPP+0]=(i+j)*128/(WIDTH+HEIGHT); /* red */
buffer[(j*WIDTH+i)*BPP+1]=i*128/WIDTH; /* green */
buffer[(j*WIDTH+i)*BPP+2]=j*256/HEIGHT; /* blue */
* simulate the passage of time
* draw a simple black line that moves down the screen. The faster the
* client, the more updates it will get, the smoother it will look!
line = now.tv_usec / (1000000/HEIGHT);
if (line>=HEIGHT) line=HEIGHT-1;
memset(&buffer[(WIDTH * BPP) * line], 0, (WIDTH * BPP));
/* frames per second (informational only) */
if (last_line > line) {
fps = fcount;
fcount = 0;
last_line = line;
fprintf(stderr,"%03d/%03d Picture (%03d fps)\r", line, HEIGHT, fps);
/* success! We have a new picture! */
return (1==1);
* Single-threaded application that interleaves client servicing with taking
* pictures from the camera. This way, we do not update the framebuffer
* while an encoding is working on it too (banding, and image artifacts).
int main(int argc,char** argv)
long usec;
rfbScreenInfoPtr server=rfbGetScreen(&argc,argv,WIDTH,HEIGHT,8,3,BPP);
return 0;
server->desktopName = "Live Video Feed Example";
/* Initialize the server */
/* Loop, processing clients and taking pictures */
while (rfbIsActive(server)) {
if (TimeToTakePicture())
if (TakePicture((unsigned char *)server->frameBuffer))
usec = server->deferUpdateTime*1000;