iidx: millisecond-based delay option (#672)

## Link to GitHub Issue or related Pull Request, if one exists
#181 

## Description of change
Use millisecond-based calculation to add artificial delay to the TT
input.

## Testing
Tested 64 bit TDJ and LDJ.

src/spice2x/games/iidx/iidx.cpp

@@ -789,17 +789,33 @@ namespace games::iidx {
         if ((player == 0 && TT_DELAY_P1 > 0) ||
             (player == 1 && TT_DELAY_P2 > 0)) {
 
-            static std::queue<uint8_t> delay_queue[2];
+            static std::queue<std::pair<double, uint8_t>> delay_queue[2];
             auto &queue = delay_queue[player];
 
-            const auto max_size =
-                static_cast<size_t>((player == 0) ? TT_DELAY_P1 : TT_DELAY_P2) + 1;
+            const auto max_delta_ms =
+                static_cast<double>((player == 0) ? TT_DELAY_P1 : TT_DELAY_P2);
 
-            queue.push(result);
-            while (queue.size() > max_size) {
+            // always push a new value
+            const auto now = get_performance_milliseconds();
+            queue.push(std::make_pair(now, result));
+            
+            // drain the queue down to reasonable length to prevent unconstrained growth
+            // this would accommodate 1 second at ~1000Hz
+            // (in reality all three iidx I/O emulation runs well under 500Hz)
+            while (queue.size() > 1024) {
                 queue.pop();
             }
-            result = queue.front();
+
+            // pop until we find one that falls just under the time threshold
+            while (!queue.empty()) {
+                const auto delta_t = now - queue.front().first;
+                if (delta_t <= max_delta_ms) {
+                    break;
+                }
+                queue.pop();
+            }
+
+            result = queue.front().second;
         }
 
         return result;

src/spice2x/launcher/options.cpp

@@ -657,21 +657,25 @@ static const std::vector<OptionDefinition> OPTION_DEFINITIONS = {
     },
     {
         // IIDXTTDelayP1
-        .title = "IIDX TT Delay Window (Player 1)",
+        .title = "IIDX TT Delay ms (Player 1)",
         .name = "iidxttdelayp1",
-        .desc = "Delays turntable by number of input polls. Duration is heavily dependent on what I/O emulation is in use. "
+        .desc = "Delays turntable by number of milliseconds. "
+            "Delay will be *at most* the specified period; maximum error is dependent on the game's poll rate. "
             "As usual, changing any option requires a restart. Default: 0 (no delay).",
         .type = OptionType::Integer,
+        .setting_name = "(0-500)",
         .game_name = "Beatmania IIDX",
         .category = "Game Options (Advanced)",
     },
     {
         // IIDXTTDelayP2
-        .title = "IIDX TT Delay Window (Player 2)",
+        .title = "IIDX TT Delay ms (Player 2)",
         .name = "iidxttdelayp2",
-        .desc = "Delays turntable by number of input polls. Duration is heavily dependent on what I/O emulation is in use. "
+        .desc = "Delays turntable by number of milliseconds. "
+            "Delay will be *at most* the specified period; maximum error is dependent on the game's poll rate. "
             "As usual, changing any option requires a restart. Default: 0 (no delay).",
         .type = OptionType::Integer,
+        .setting_name = "(0-500)",
         .game_name = "Beatmania IIDX",
         .category = "Game Options (Advanced)",
     },