From a7f7fb9e6a7763320210e9938cd5867b894c6926 Mon Sep 17 00:00:00 2001
From: hap <happppp@users.noreply.github.com>
Date: Fri, 14 Aug 2020 20:43:54 +0200
Subject: [PATCH] i8244: add external collision detection

---
 src/devices/video/i8244.cpp   | 18 ++++++++++++++++++
 src/devices/video/i8244.h     |  1 +
 src/mame/drivers/odyssey2.cpp | 10 ++++++++--
 3 files changed, 27 insertions(+), 2 deletions(-)

diff --git a/src/devices/video/i8244.cpp b/src/devices/video/i8244.cpp
index 35733a9da24..2b2526b71ac 100644
--- a/src/devices/video/i8244.cpp
+++ b/src/devices/video/i8244.cpp
@@ -469,6 +469,24 @@ int i8244_device::hblank()
 }
 
 
+void i8244_device::write_cx(int x, bool cx)
+{
+	if (cx)
+	{
+		// Check if we collide with an already drawn source object
+		if ( m_vdc.s.collision & m_collision_map[x] )
+		{
+			m_collision_status |= 0x40;
+		}
+		// Check if an already drawn object would collide with us
+		if ( m_vdc.s.collision & 0x40 )
+		{
+			m_collision_status |= m_collision_map[x];
+		}
+	}
+}
+
+
 uint32_t i8244_device::screen_update(screen_device &screen, bitmap_ind16 &bitmap, const rectangle &cliprect)
 {
 	// Some local constants for this method
diff --git a/src/devices/video/i8244.h b/src/devices/video/i8244.h
index 685ba1fb6a2..d27ae19ea52 100644
--- a/src/devices/video/i8244.h
+++ b/src/devices/video/i8244.h
@@ -35,6 +35,7 @@ public:
 
 	uint8_t read(offs_t offset);
 	void write(offs_t offset, uint8_t data);
+	void write_cx(int x, bool cx); // CX pin on current scanline
 
 	int vblank();
 	int hblank();
diff --git a/src/mame/drivers/odyssey2.cpp b/src/mame/drivers/odyssey2.cpp
index f638f336871..e7420a31569 100644
--- a/src/mame/drivers/odyssey2.cpp
+++ b/src/mame/drivers/odyssey2.cpp
@@ -45,7 +45,6 @@ TODO:
   be correct(see backgamm)
 - ppp(the tetris game) does not work properly on PAL, is this homebrew NTSC-only,
   or is it due to PAL video timing? The game does mid-scanline updates
-- add 824x vs ef934x collision detection, none of the games use it
 - g7400 rally doesn't work, car keeps exploding, it is related to ef9341_read:
   If you invert the returned RAM value, the USA map looks better. If you always
   return 0, the game can be played but the car is invincible
@@ -502,7 +501,7 @@ uint32_t g7400_state::screen_update(screen_device &screen, bitmap_ind16 &bitmap,
 				// Use EF934x input
 				d = ef934x_bitmap->pix16( y - yoffs, x - xoffs ) & 0x07;
 
-				if ( ! m_ic674_decode[ d & 0x07 ] )
+				if ( ! m_ic674_decode[ d ] )
 				{
 					d |= 0x08;
 				}
@@ -511,6 +510,13 @@ uint32_t g7400_state::screen_update(screen_device &screen, bitmap_ind16 &bitmap,
 			{
 				// Use i8245 input
 				d |= lum;
+
+				// I outputs to CX
+				if (x >= xoffs && x < (320 + xoffs) && y >= yoffs)
+				{
+					bool cx = !m_ic674_decode[ef934x_bitmap->pix16(y - yoffs, x - xoffs) & 0x07];
+					m_i8244->write_cx(x, cx);
+				}
 			}
 			bitmap.pix16(y, x) = d;
 		}