Added an example camera application to demonstrate another way to write a server application.

2 files changed, 154 insertions, 1 deletions

diff --git a/examples/Makefile.am b/examples/Makefile.am
index 644f017..c2ef6fa 100644
--- a/examples/Makefile.am
+++ b/examples/Makefile.am
@@ -18,5 +18,5 @@ noinst_HEADERS=radon.h
 
 noinst_PROGRAMS=example pnmshow regiontest pnmshow24 fontsel \
 	vncev storepasswd colourmaptest simple simple15 $(MAC) \
-	$(FILETRANSFER) backchannel $(BLOOPTEST)
+	$(FILETRANSFER) backchannel $(BLOOPTEST) camera
 
diff --git a/examples/camera.c b/examples/camera.c
new file mode 100644
index 0000000..f46f5c7
--- /dev/null
+++ b/examples/camera.c
@@ -0,0 +1,153 @@
+
+/*
+ * 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 seperate 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 seperate 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 <malloc.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;
+
+    gettimeofday(&now,NULL);
+
+    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 */
+    }
+    buffer[j*WIDTH*BPP+0]=0xff;
+    buffer[j*WIDTH*BPP+1]=0xff;
+    buffer[j*WIDTH*BPP+2]=0xff;
+  }
+
+  /*
+   * 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!
+   */
+  gettimeofday(&now,NULL);
+  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) */
+  fcount++;
+  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);
+  server->desktopName = "Live Video Feed Example";
+  server->frameBuffer=(char*)malloc(WIDTH*HEIGHT*BPP);
+  server->alwaysShared=(1==1);
+
+  /* Initialize the server */
+  rfbInitServer(server);           
+
+  /* Loop, processing clients and taking pictures */
+  while (rfbIsActive(server)) {
+    if (TimeToTakePicture())
+      if (TakePicture((unsigned char *)server->frameBuffer))
+        rfbMarkRectAsModified(server,0,0,WIDTH,HEIGHT);
+          
+    usec = server->deferUpdateTime*1000;
+    rfbProcessEvents(server,usec);
+  }
+  return(0);
+}