segas32: fix NBG0 - NBG3 layer flip (#14193)

Author: mahoneyt944

src/mame/sega/segas32_v.cpp

@@ -20,11 +20,8 @@
     - Verify that X/Y center has 10 bits of resolution when zooming and
       9 when not.
 
-    - In svf (the field) and radr (on the field), they use tilemap-specific
-      flip in conjunction with rowscroll AND rowselect. According to Charles,
-      in this case, the rowselect lookups should be done in reverse order,
-      but this results in an incorrect display. For now, we assume there is
-      a bug in the procedure and implement it so that it looks correct.
+    - Sonic while globally flipped via the service menu, fails to flip
+      the "SEGA" and "SEGASONIC" sprite based logos on the title screen.
 
     - titlef NBG0 and NBG2 layers are currently hidden during gameplay.
       It sets $31ff02 with either $7be0 and $2960 (and $31ff8e is $c00).
@@ -61,8 +58,8 @@
          $31FF00 : w--- ---- ---- ---- : Screen width (0= 320, 1= 412)
                    ---- f--- ---- ---- : Bitmap format (1= 8bpp, 0= 4bpp)
                    ---- -t-- ---- ---- : Tile banking related
-                   ---- --f- ---- ---- : 1= Global X/Y flip? (most games?)
-                   ---- ---f ---- ---- : 1= prohbit Y flip? (Air Rescue 2nd screen title, also gets set on one of the intro sequence screens)
+                   ---- --f- ---- ---- : 1= Global X/Y flip (enabled via service menu)
+                   ---- ---f ---- ---- : 1= Prohibit layer Y flip (NBG0 - NBG3)
                    ---- ---- ---- 4--- : 1= X+Y flip for NBG3
                    ---- ---- ---- -2-- : 1= X+Y flip for NBG2
                    ---- ---- ---- --1- : 1= X+Y flip for NBG1
@@ -544,7 +541,7 @@ TILE_GET_INFO_MEMBER(segas32_state::get_tile_info)
 
 int segas32_state::compute_clipping_extents(screen_device &screen, int enable, int clipout, int clipmask, const rectangle &cliprect, extents_list *list)
 {
-	int flip = (m_videoram[0x1ff00/2] >> 9) & 1;
+	int flip = BIT(m_videoram[0x1ff00 / 2], 9);
 	rectangle tempclip;
 	rectangle clips[5];
 	int sorted[5];
@@ -646,20 +643,14 @@ int segas32_state::compute_clipping_extents(screen_device &screen, int enable, i
 
 void segas32_state::compute_tilemap_flips(int bgnum, int &flipx, int &flipy)
 {
-	/* determine if we're flipped */
-	int global_flip = (m_videoram[0x1ff00 / 2] >> 9)&1;
-
-	flipx = global_flip;
-	flipy = global_flip;
-
-	int layer_flip = (m_videoram[0x1ff00 / 2] >> bgnum) & 1;
+	// determine flip bits
+	int global_flip    = BIT(m_videoram[0x1ff00 / 2], 9);
+	int layer_flip     = BIT(m_videoram[0x1ff00 / 2], bgnum);
+	int prohibit_flipy = BIT(m_videoram[0x1ff00 / 2], 8);
 
-	flipy ^= layer_flip;
-	flipx ^= layer_flip;
+	flipx = (layer_flip) ? !global_flip : global_flip;
 
-	// this bit is set on Air Rescue (screen 2) title screen, during the Air Rescue introduction demo, and in f1en when you win a single player race
-	// it seems to prohibit (at least) the per-tilemap y flipping (maybe global y can override it)
-	if ((m_videoram[0x1ff00 / 2] >> 8) & 1) flipy = 0;
+	flipy = (layer_flip && !prohibit_flipy) ? !global_flip : global_flip;
 }
 
 /*************************************
@@ -705,7 +696,7 @@ void segas32_state::update_tilemap_zoom(screen_device &screen, segas32_state::la
 //if (screen.machine().input().code_pressed(KEYCODE_X) && bgnum == 1) opaque = 1;
 	int flipx, flipy;
 
-	// todo determine flipping
+	// determine flipping
 	compute_tilemap_flips(bgnum, flipx, flipy);
 
 	/* determine the clipping */
@@ -863,7 +854,7 @@ void segas32_state::update_tilemap_rowscroll(screen_device &screen, segas32_stat
 
 	int flipx, flipy;
 
-	// todo determine flipping
+	// determine flipping
 	compute_tilemap_flips(bgnum, flipx, flipy);
 
 
@@ -914,21 +905,24 @@ void segas32_state::update_tilemap_rowscroll(screen_device &screen, segas32_stat
 			}
 
 			int srcy;
+			int ylookup;
 			if (!flipy)
 			{
 				srcy = yscroll + y;
+				ylookup = y;
 			}
 			else
 			{
 				const rectangle &visarea = screen.visible_area();
 				srcy = yscroll + visarea.max_y - y;
+				ylookup = visarea.max_y - y;
 			}
 
 			/* apply row scroll/select */
 			if (rowscroll)
-				srcx += table[0x000 + 0x100 * (bgnum - 2) + y] & 0x3ff;
+				srcx += table[0x000 + 0x100 * (bgnum - 2) + ylookup] & 0x3ff;
 			if (rowselect)
-				srcy = (yscroll + table[0x200 + 0x100 * (bgnum - 2) + y]) & 0x1ff;
+				srcy = (yscroll + table[0x200 + 0x100 * (bgnum - 2) + ylookup]) & 0x1ff;
 
 
 			/* look up the pages and get their source pixmaps */
@@ -996,7 +990,7 @@ void segas32_state::update_tilemap_text(screen_device &screen, segas32_state::la
 	bitmap_ind16 &bitmap = layer.bitmap;
 
 	/* determine if we're flipped */
-	int flip = (m_videoram[0x1ff00/2] >> 9) & 1;
+	int flip = BIT(m_videoram[0x1ff00 / 2], 9);
 
 	/* determine the base of the tilemap and graphics data */
 	uint16_t const *const tilebase = &m_videoram[((m_videoram[0x1ff5c/2] >> 4) & 0x1f) * 0x800];