pstats: Don't compute frame data for dropped frames

When a frame is dropped, the previous non-dropped frame is considered to be repeated, but the strip chart would compute new cached frame data for it, causing performance to be unusably slow at high frame rate data gathering even when most frames are skipped

This makes performance remotely usable in that situation

pandatool/src/pstatserver/pStatStripChart.cxx

@@ -590,6 +590,7 @@ get_frame_data(int frame_number) const {
   }
 
   const PStatThreadData *thread_data = _view.get_thread_data();
+  //assert(thread_data->has_frame(frame_number));
   const PStatFrameData &frame_data = thread_data->get_frame(frame_number);
   _view.set_to_frame(frame_data);
 
@@ -659,24 +660,26 @@ compute_average_pixel_data(PStatStripChart::FrameData &result,
   then_i = thread_data->get_frame_number_after(then, then_i);
   now_i = thread_data->get_frame_number_after(now, now_i);
 
-  const FrameData &then_fdata = get_frame_data(then_i);
-  then = max(then, then_fdata._start);
-  double then_end = then_fdata._end;
+  const FrameData *fdata = &get_frame_data(then_i);
+  then = max(then, fdata->_start);
+  double then_end = fdata->_end;
 
   // Sum up a weighted average of all of the individual frames we pass.
 
   // We start with just the portion of frame then_i that actually does fall
   // within our "then to now" window.
-  accumulate_frame_data(result, then_fdata, then_end - then);
+  accumulate_frame_data(result, *fdata, then_end - then);
   double last = then_end;
 
   // Then we get all of each of the middle frames.
   for (int frame_number = then_i + 1;
        frame_number < now_i;
        frame_number++) {
-    const FrameData &fdata = get_frame_data(frame_number);
-    accumulate_frame_data(result, fdata, fdata._end - last);
-    last = fdata._end;
+    if (thread_data->has_frame(frame_number)) {
+      fdata = &get_frame_data(frame_number);
+    }
+    accumulate_frame_data(result, *fdata, fdata->_end - last);
+    last = fdata->_end;
   }
 
   // And finally, we get the remainder as now_i.
@@ -729,19 +732,21 @@ get_average_net_value() const {
     // We start with just the portion of frame then_i that actually does fall
     // within our "then to now" window (usually some portion of it will).
     const PStatFrameData &frame_data = thread_data->get_frame(then_i);
+    const FrameData *frame = &get_frame_data(then_i);
     if (frame_data.get_end() > then) {
-      const FrameData &frame = get_frame_data(then_i);
-      double this_time = (frame._end - then);
-      net_value += frame._net_value * this_time;
+      double this_time = (frame->_end - then);
+      net_value += frame->_net_value * this_time;
       net_time += this_time;
     }
     // Then we get all of each of the remaining frames.
     for (int frame_number = then_i + 1;
          frame_number <= now_i;
          frame_number++) {
-      const FrameData &frame = get_frame_data(frame_number);
-      double this_time = frame._net_time;
-      net_value += frame._net_value * this_time;
+      if (thread_data->has_frame(frame_number)) {
+        frame = &get_frame_data(frame_number);
+      }
+      double this_time = frame->_net_time;
+      net_value += frame->_net_value * this_time;
       net_time += this_time;
     }