add simple step forward and backward

src/emulator/emu.rs

@@ -40,7 +40,8 @@ pub struct MyEmulator {
     pub pixel_format: Option<crate::video::video_buffer::PixelFormat>,
 
     pub memory_map: Option<LibRetroMemoryMap>,
-    pub paused: bool
+    pub paused: bool,
+    pub frames_to_run_before_pause: Option<u32>,
 }
 
 impl MyEmulator {
@@ -84,7 +85,8 @@ impl MyEmulator {
             video_buffer: None,
             pixel_format: None,
             memory_map: None,
-            paused: false
+            paused: false,
+            frames_to_run_before_pause: None
         };
         let mut pin_emu = Box::pin(emu);
         retro::wrapper::set_handler(pin_emu.as_mut());
@@ -93,6 +95,17 @@ impl MyEmulator {
     }
 
     pub fn run_frame(&mut self){
+        if let Some(frames_to_run_before_pause) = self.frames_to_run_before_pause {
+            if frames_to_run_before_pause > 0 {
+                self.frames_to_run_before_pause = Some(frames_to_run_before_pause - 1);
+            }
+            else if frames_to_run_before_pause == 0 {
+                self.paused = true;
+                self.frames_to_run_before_pause = None;
+            }
+
+        }
+
         if !self.paused {
             self.frame += 1;
             self.retro.run();

src/ui/debug_window.rs

@@ -19,6 +19,8 @@ widget_ids!(struct Ids {
     save_button,
     load_button,
     pause_button,
+    advance_button,
+    rewind_button,
     search_box,
     watch_list,
     watch_background,
@@ -37,6 +39,7 @@ pub struct DebugWindow {
     search: MemorySearch,
     watches: Vec<MemoryWatch>,
     watches_selected: HashSet<usize>,
+    step_backward_states: Vec<Vec<u8>>,
 }
 impl DebugWindow {
     pub fn new(event_loop: &EventLoop<()>, emu: &Rc<RefCell<Pin<Box<MyEmulator>>>>) -> Box<Self> {
@@ -71,6 +74,7 @@ impl DebugWindow {
             search: MemorySearch::new(),
             watches: Vec::new(),
             watches_selected: HashSet::new(),
+            step_backward_states: Vec::new(),
         })
     }
 
@@ -146,7 +150,7 @@ impl TrackedWindow for DebugWindow {
 
 
                 if widget::Button::new()
-                    .label("pause")
+                    .label(if emu.paused {"resume"} else {"pause"})
                     .right_from(self.ids.load_button, 8.0)
                     .label_font_size(14)
                     .w_h(96.0, 32.0)
@@ -154,6 +158,50 @@ impl TrackedWindow for DebugWindow {
                     .was_clicked()
                     {
                         emu.paused = !emu.paused;
+                        self.step_backward_states.clear();
+                    }
+
+                if widget::Button::new()
+                    .label("forward 1")
+                    .down_from(self.ids.pause_button, 8.0)
+                    .label_font_size(14)
+                    .w_h(96.0, 32.0)
+                    .set(self.ids.advance_button, &mut ui)
+                    .was_clicked()
+                    {
+                        match emu.retro.serialize() {
+                            Ok(data) => self.step_backward_states.push(data),
+                            Err(e) => eprintln!("Problem serializing backward state {:?}", e),
+                        }
+                        emu.frames_to_run_before_pause = Some(1);
+                        emu.paused = false;
+                    }
+
+                if widget::Button::new()
+                    .label("back 1")
+                    .down_from(self.ids.load_button, 8.0)
+                    .label_font_size(14)
+                    .w_h(96.0, 32.0)
+                    .set(self.ids.rewind_button, &mut ui)
+                    .was_clicked()
+                    {
+                        match self.step_backward_states.pop() {
+                            Some(data) => {
+                                match self.step_backward_states.pop() {
+                                    Some(data) => {
+                                        emu.retro.unserialize(data.as_slice());
+                                        emu.frames_to_run_before_pause = Some(1);
+                                        emu.paused = false;
+                                    }
+                                    None => {
+                                        eprintln!("No more backward states available (need 2)");
+                                    },
+                                }
+                            },
+                            None => {
+                                eprintln!("No more backward states available");
+                            },
+                        }
                     }
 
                 let mut memory = emu.retro.get_memory(2);