Correct downsampling and better layout

src/config.cpp

@@ -3,6 +3,10 @@
 
 #include "config.hpp"
 
+// For `RowSet::kMaxRows`: `--plots` names a row count, and one constant for the ceiling
+// is what stops the message and the clamp from drifting apart.
+#include "plot_host.hpp"
+
 #include <cstdio>
 #include <cstdlib>
 #include <stdexcept>
@@ -48,7 +52,8 @@ void print_usage(std::FILE* out, const char* argv0) {
                "  --max-window SEC     largest time window the toolbar offers (default 600)\n"
                "  --holdoff SEC        default trigger hold-off (default 0.010)\n"
                "  --recv-buffer BYTES  SO_RCVBUF for the receiver socket (default 8388608)\n"
-               "  --plots N            initial number of stacked plots, 1..4 (default 1)\n"
+               "  --plots N            stacked plots to start with, 1..8 (default 1); rows are\n"
+               "                       added and removed from the layout editor\n"
                "  -h, --help           this text\n",
                argv0);
 }
@@ -88,7 +93,9 @@ Config parse_args(int argc, char** argv) {
     } else if (a == "--plots" || a.rfind("--plots=", 0) == 0) {
       const std::string v = value_of(argc, argv, i, "--plots");
       const long n = std::strtol(v.c_str(), nullptr, 10);
-      if (n < 1 || n > 4) fail("--plots must be 1..4: " + v);
+      if (n < 1 || n > RowSet::kMaxRows) {
+        fail("--plots must be 1.." + std::to_string(RowSet::kMaxRows) + ": " + v);
+      }
       c.plots = static_cast<int>(n);
     } else {
       fail("unknown argument: " + a);