1
2 /**
3 * @example camera.c
4 * Question: I need to display a live camera image via VNC. Until now I just
5 * grab an image, set the rect to modified and do a 0.1 s sleep to give the
6 * system time to transfer the data.
7 * This is obviously a solution which doesn't scale very well to different
8 * connection speeds/cpu horsepowers, so I wonder if there is a way for the
9 * server application to determine if the updates have been sent. This would
10 * cause the live image update rate to always be the maximum the connection
11 * supports while avoiding excessive loads.
12 *
13 * Thanks in advance,
14 *
15 *
16 * Christian Daschill
17 *
18 *
19 * Answer: Originally, I thought about using seperate threads and using a
20 * mutex to determine when the frame buffer was being accessed by any client
21 * so we could determine a safe time to take a picture. The probem is, we
22 * are lock-stepping everything with framebuffer access. Why not be a
23 * single-thread application and in-between rfbProcessEvents perform a
24 * camera snapshot. And this is what I do here. It guarantees that the
25 * clients have been serviced before taking another picture.
26 *
27 * The downside to this approach is that the more clients you have, there is
28 * less time available for you to service the camera equating to reduced
29 * frame rate. (or, your clients are on really slow links). Increasing your
30 * systems ethernet transmit queues may help improve the overall performance
31 * as the libvncserver should not stall on transmitting to any single
32 * client.
33 *
34 * Another solution would be to provide a seperate framebuffer for each
35 * client and use mutexes to determine if any particular client is ready for
36 * a snapshot. This way, your not updating a framebuffer for a slow client
37 * while it is being transferred.
38 */
39
40 #include <stdio.h>
41 #include <stdlib.h>
42 #include <string.h>
43 #include <rfb/rfb.h>
44
45
46 #define WIDTH 640
47 #define HEIGHT 480
48 #define BPP 4
49
50 /* 15 frames per second (if we can) */
51 #define PICTURE_TIMEOUT (1.0/15.0)
52
53
54 /*
55 * throttle camera updates
56 */
TimeToTakePicture()57 int TimeToTakePicture() {
58 static struct timeval now={0,0}, then={0,0};
59 double elapsed, dnow, dthen;
60
61 gettimeofday(&now,NULL);
62
63 dnow = now.tv_sec + (now.tv_usec /1000000.0);
64 dthen = then.tv_sec + (then.tv_usec/1000000.0);
65 elapsed = dnow - dthen;
66
67 if (elapsed > PICTURE_TIMEOUT)
68 memcpy((char *)&then, (char *)&now, sizeof(struct timeval));
69 return elapsed > PICTURE_TIMEOUT;
70 }
71
72
73
74 /*
75 * simulate grabbing a picture from some device
76 */
TakePicture(unsigned char * buffer)77 int TakePicture(unsigned char *buffer)
78 {
79 static int last_line=0, fps=0, fcount=0;
80 int line=0;
81 int i,j;
82 struct timeval now;
83
84 /*
85 * simulate grabbing data from a device by updating the entire framebuffer
86 */
87
88 for(j=0;j<HEIGHT;++j) {
89 for(i=0;i<WIDTH;++i) {
90 buffer[(j*WIDTH+i)*BPP+0]=(i+j)*128/(WIDTH+HEIGHT); /* red */
91 buffer[(j*WIDTH+i)*BPP+1]=i*128/WIDTH; /* green */
92 buffer[(j*WIDTH+i)*BPP+2]=j*256/HEIGHT; /* blue */
93 }
94 buffer[j*WIDTH*BPP+0]=0xff;
95 buffer[j*WIDTH*BPP+1]=0xff;
96 buffer[j*WIDTH*BPP+2]=0xff;
97 }
98
99 /*
100 * simulate the passage of time
101 *
102 * draw a simple black line that moves down the screen. The faster the
103 * client, the more updates it will get, the smoother it will look!
104 */
105 gettimeofday(&now,NULL);
106 line = now.tv_usec / (1000000/HEIGHT);
107 if (line>HEIGHT) line=HEIGHT-1;
108 memset(&buffer[(WIDTH * BPP) * line], 0, (WIDTH * BPP));
109
110 /* frames per second (informational only) */
111 fcount++;
112 if (last_line > line) {
113 fps = fcount;
114 fcount = 0;
115 }
116 last_line = line;
117 fprintf(stderr,"%03d/%03d Picture (%03d fps)\r", line, HEIGHT, fps);
118
119 /* success! We have a new picture! */
120 return (1==1);
121 }
122
123
124
125
126 /*
127 * Single-threaded application that interleaves client servicing with taking
128 * pictures from the camera. This way, we do not update the framebuffer
129 * while an encoding is working on it too (banding, and image artifacts).
130 */
main(int argc,char ** argv)131 int main(int argc,char** argv)
132 {
133 long usec;
134
135 rfbScreenInfoPtr server=rfbGetScreen(&argc,argv,WIDTH,HEIGHT,8,3,BPP);
136 if(!server)
137 return 0;
138 server->desktopName = "Live Video Feed Example";
139 server->frameBuffer=(char*)malloc(WIDTH*HEIGHT*BPP);
140 server->alwaysShared=(1==1);
141
142 /* Initialize the server */
143 rfbInitServer(server);
144
145 /* Loop, processing clients and taking pictures */
146 while (rfbIsActive(server)) {
147 if (TimeToTakePicture())
148 if (TakePicture((unsigned char *)server->frameBuffer))
149 rfbMarkRectAsModified(server,0,0,WIDTH,HEIGHT);
150
151 usec = server->deferUpdateTime*1000;
152 rfbProcessEvents(server,usec);
153 }
154 return(0);
155 }
156