From f2d3f5ec071a2ae4a69b047fd49e7827c11a700c Mon Sep 17 00:00:00 2001
From: Simon Gellis <simongellis@gmail.com>
Date: Tue, 25 Feb 2025 00:04:07 -0500
Subject: [PATCH] Implement frame advance

---
 src/emulator.rs    | 32 +++++++++++++++++++++++++++++++-
 src/window/game.rs |  9 +++++++++
 2 files changed, 40 insertions(+), 1 deletion(-)

diff --git a/src/emulator.rs b/src/emulator.rs
index 066e318..94156fe 100644
--- a/src/emulator.rs
+++ b/src/emulator.rs
@@ -291,6 +291,26 @@ impl Emulator {
         );
     }
 
+    fn frame_advance(&mut self) {
+        if self
+            .state
+            .compare_exchange(
+                EmulatorState::Paused,
+                EmulatorState::Stepping,
+                Ordering::AcqRel,
+                Ordering::Acquire,
+            )
+            .is_err_and(|s| s == EmulatorState::Running)
+        {
+            let _ = self.state.compare_exchange(
+                EmulatorState::Running,
+                EmulatorState::Stepping,
+                Ordering::AcqRel,
+                Ordering::Relaxed,
+            );
+        }
+    }
+
     fn save_sram(&mut self, sim_id: SimId) -> Result<()> {
         let sim = self.sims.get_mut(sim_id.to_index());
         let cart = self.carts[sim_id.to_index()].as_mut();
@@ -366,6 +386,7 @@ impl Emulator {
         debugger.stop_reason = None;
         true
     }
+
     fn debug_step(&mut self, sim_id: SimId) {
         if self.debug_continue(sim_id) {
             let Some(sim) = self.sims.get_mut(sim_id.to_index()) else {
@@ -428,7 +449,7 @@ impl Emulator {
         // Don't emulate if the state is "paused", or if any sim is paused in the debugger
         let running = match state {
             EmulatorState::Paused => false,
-            EmulatorState::Running => true,
+            EmulatorState::Running | EmulatorState::Stepping => true,
             EmulatorState::Debugging => self.debuggers.values().all(|d| d.stop_reason.is_none()),
         };
         let p1_running = running && p1_state == SimState::Ready;
@@ -442,6 +463,10 @@ impl Emulator {
             self.sims[SimId::Player2.to_index()].emulate();
         }
 
+        if state == EmulatorState::Stepping {
+            self.state.store(EmulatorState::Paused, Ordering::Release);
+        }
+
         // Debug state
         if state == EmulatorState::Debugging {
             for sim_id in SimId::values() {
@@ -539,6 +564,9 @@ impl Emulator {
             EmulatorCommand::Resume => {
                 self.resume_sims();
             }
+            EmulatorCommand::FrameAdvance => {
+                self.frame_advance();
+            }
             EmulatorCommand::StartDebugging(sim_id, debugger) => {
                 self.start_debugging(sim_id, debugger);
             }
@@ -665,6 +693,7 @@ pub enum EmulatorCommand {
     StopSecondSim,
     Pause,
     Resume,
+    FrameAdvance,
     StartDebugging(SimId, DebugSender),
     StopDebugging(SimId),
     DebugInterrupt(SimId),
@@ -700,6 +729,7 @@ pub enum SimState {
 pub enum EmulatorState {
     Paused,
     Running,
+    Stepping,
     Debugging,
 }
 
diff --git a/src/window/game.rs b/src/window/game.rs
index 53d6484..ce78bd2 100644
--- a/src/window/game.rs
+++ b/src/window/game.rs
@@ -86,6 +86,7 @@ impl GameWindow {
             let is_ready = self.client.sim_state(self.sim_id) == SimState::Ready;
             let can_pause = is_ready && state == EmulatorState::Running;
             let can_resume = is_ready && state == EmulatorState::Paused;
+            let can_frame_advance = is_ready && state != EmulatorState::Debugging;
             if state == EmulatorState::Running {
                 if ui.add_enabled(can_pause, Button::new("Pause")).clicked() {
                     self.client.send_command(EmulatorCommand::Pause);
@@ -100,6 +101,14 @@ impl GameWindow {
                     .send_command(EmulatorCommand::Reset(self.sim_id));
                 ui.close_menu();
             }
+            ui.separator();
+            if ui
+                .add_enabled(can_frame_advance, Button::new("Frame Advance"))
+                .clicked()
+            {
+                self.client.send_command(EmulatorCommand::FrameAdvance);
+                ui.close_menu();
+            }
         });
         ui.menu_button("Options", |ui| self.show_options_menu(ctx, ui));
         ui.menu_button("Multiplayer", |ui| {