From eb9d457eb0101b8e15773024307d806b2a37cc13 Mon Sep 17 00:00:00 2001
From: Enik Land <enikland2@gmx.com>
Date: Tue, 16 Sep 2025 20:37:28 -0300
Subject: [PATCH] Move switching of screen's current bitmap to after layout
 updates

---
 src/emu/screen.cpp | 25 ++++++++++++++++++++++---
 src/emu/screen.h   |  1 +
 src/emu/video.cpp  | 17 +++++++++++++++++
 src/emu/video.h    |  1 +
 4 files changed, 41 insertions(+), 3 deletions(-)

diff --git a/src/emu/screen.cpp b/src/emu/screen.cpp
index 849c1dff8bb1c..3c49a6d5e6766 100644
--- a/src/emu/screen.cpp
+++ b/src/emu/screen.cpp
@@ -1779,7 +1779,6 @@ bool screen_device::update_quads()
 				}
 				m_texture[m_curbitmap]->set_bitmap(m_bitmap[m_curbitmap], m_visarea, m_bitmap[m_curbitmap].texformat());
 				m_curtexture = m_curbitmap;
-				m_curbitmap = 1 - m_curbitmap;
 			}
 
 			// brightness adjusted render color
@@ -1791,10 +1790,30 @@ bool screen_device::update_quads()
 		}
 	}
 
+	return m_changed;
+}
+
+
+//-------------------------------------------------
+//  switch current bitmap
+//-------------------------------------------------
+
+void screen_device::switch_current_bitmap()
+{
+	// only updated if live
+	if (machine().render().is_live(*this))
+	{
+		// only updated if empty and not a vector game; otherwise assume the driver did it directly
+		if (m_type != SCREEN_TYPE_VECTOR && (m_video_attributes & VIDEO_SELF_RENDER) == 0)
+		{
+			// if we're not skipping the frame and if the screen actually changed, then switch the bitmap
+			if (!machine().video().skip_this_frame() && m_changed)
+				m_curbitmap = 1 - m_curbitmap;
+		}
+	}
+
 	// reset the screen changed flags
-	bool result = m_changed;
 	m_changed = false;
-	return result;
 }
 
 
diff --git a/src/emu/screen.h b/src/emu/screen.h
index ddc7510d8f722..00e1b7f08875c 100644
--- a/src/emu/screen.h
+++ b/src/emu/screen.h
@@ -415,6 +415,7 @@ class screen_device : public device_t
 
 	// internal to the video system
 	bool update_quads();
+	void switch_current_bitmap();
 	void update_burnin();
 
 	// globally accessible constants
diff --git a/src/emu/video.cpp b/src/emu/video.cpp
index 75ba128df91fe..c540aab3e40bf 100644
--- a/src/emu/video.cpp
+++ b/src/emu/video.cpp
@@ -244,6 +244,10 @@ void video_manager::frame_update(bool from_debugger)
 		machine().osd().update(!from_debugger && skipped_it);
 	}
 
+	// prepare screens for next frame
+	if (update_screens)
+		post_screen_updates();
+
 	// we synchronize after rendering instead of before, if low latency mode is enabled
 	if (!from_debugger && phase > machine_phase::INIT && m_low_latency && effective_throttle())
 		update_throttle(current_time);
@@ -655,6 +659,19 @@ bool video_manager::finish_screen_updates()
 }
 
 
+//-------------------------------------------------
+//  post_screen_updates - prepare screens for next
+//  frame
+//-------------------------------------------------
+
+void video_manager::post_screen_updates()
+{
+	screen_device_enumerator iter(machine().root_device());
+
+	for (screen_device &screen : iter)
+		screen.switch_current_bitmap();
+}
+
 
 //-------------------------------------------------
 //  update_throttle - throttle to the game's
diff --git a/src/emu/video.h b/src/emu/video.h
index 6517c90d170bf..1579277585810 100644
--- a/src/emu/video.h
+++ b/src/emu/video.h
@@ -101,6 +101,7 @@ class video_manager
 	// speed and throttling helpers
 	int original_speed_setting() const;
 	bool finish_screen_updates();
+	void post_screen_updates();
 	void update_throttle(attotime emutime);
 	osd_ticks_t throttle_until_ticks(osd_ticks_t target_ticks);
 	void update_frameskip();