From 02def869af45f3d89f658dd9b180a1f1c6093c95 Mon Sep 17 00:00:00 2001
From: Andrei Holub <andrei.holub@gmail.com>
Date: Fri, 24 Oct 2025 12:37:56 -0400
Subject: [PATCH] sinclair/specnext_sprites.cpp: Detected sprites collision

---
 src/mame/sinclair/specnext_sprites.cpp | 46 ++++++++++++++++++++------
 1 file changed, 36 insertions(+), 10 deletions(-)

diff --git a/src/mame/sinclair/specnext_sprites.cpp b/src/mame/sinclair/specnext_sprites.cpp
index c9173a97ac40b..c1192927c3dbf 100644
--- a/src/mame/sinclair/specnext_sprites.cpp
+++ b/src/mame/sinclair/specnext_sprites.cpp
@@ -78,8 +78,8 @@ void specnext_sprites_device::draw(screen_device &screen, bitmap_rgb32 &bitmap,
 
 	for (auto i = 0; i < m_sprites_cache.size(); i++ )
 	{
-		const u8 x = m_zero_on_top ? i : (m_sprites_cache.size() - 1) - i;
-		const sprite_data &spr = m_sprites_cache[x];
+		const u8 n = m_zero_on_top ? i : (m_sprites_cache.size() - 1) - i;
+		const sprite_data &spr = m_sprites_cache[n];
 
 		gfx((spr.rotate << 1) | spr.h)->prio_zoom_transpen(bitmap, clipped
 			, spr.pattern >> (1 - spr.h), spr.paloff
@@ -207,20 +207,46 @@ u8 specnext_sprites_device::status_r()
 	bool collision = 0;
 	for (auto s1 = begin(m_sprites_cache); !collision && s1 != end(m_sprites_cache); ++s1)
 	{
+		const u8 t_pen1 = m_transp_colour & (s1->h ? 0x0f : 0xff);
 		const u16 x1 = s1->x & 0x1ff;
-		const u16 w1 = 16 << ((s1->rotate & 1) ? s1->yscale : s1->xscale);
 		const u16 y1 = s1->y & 0x1ff;
-		const u16 h1 = 16 << ((s1->rotate & 1) ? s1->xscale : s1->yscale);
+		const rectangle rec1 = {
+			x1, x1 + (16 << ((s1->rotate & 1) ? s1->yscale : s1->xscale)) - 1,
+			y1, y1 + (16 << ((s1->rotate & 1) ? s1->xscale : s1->yscale)) - 1
+		};
 		for (auto s2 = s1 + 1; !collision && s2 != end(m_sprites_cache); ++s2)
 		{
 			const u16 x2 = s2->x & 0x1ff;
-			const u16 w2 = 16 << ((s2->rotate & 1) ? s2->yscale : s2->xscale);
 			const u16 y2 = s2->y & 0x1ff;
-			const u16 h2 = 16 << ((s2->rotate & 1) ? s2->xscale : s2->yscale);
-			bool c = (x1 < x2 + w2) && (x2 < x1 + w1) && (y1 < y2 + h2) && (y2 < y1 + h1);
-			if (c)
-				; // TODO detect if pixel(s) are not transparent
-			collision |= c;
+			rectangle over = rec1 & rectangle {
+				x2, x2 + (16 << ((s2->rotate & 1) ? s2->yscale : s2->xscale)) - 1,
+				y2, y2 + (16 << ((s2->rotate & 1) ? s2->xscale : s2->yscale)) - 1
+			};
+			if (!over.empty()) // sprites overlapped
+			{
+				const u8 t_pen2 = m_transp_colour & (s2->h ? 0x0f : 0xff);
+				bitmap_ind16 b1 = bitmap_ind16(16 << 3, 1);
+				bitmap_ind16 b2 = bitmap_ind16(16 << 3, 1);
+				for (u16 y = over.top(); y <= over.bottom(); ++y) // draw one line of the time in the overlap area
+				{
+					gfx((s1->rotate << 1) | s1->h)->zoom_opaque(b1, { 0, over.width() - 1, 0, 0 }
+						, s1->pattern >> (1 - s1->h), 0
+						, s1->xmirror, s1->ymirror
+						, x1 - over.left(), y1 - y
+						, 0x10000 << s1->xscale, 0x10000 << s1->yscale);
+					gfx((s2->rotate << 1) | s2->h)->zoom_opaque(b2, { 0, over.width() - 1, 0, 0 }
+						, s2->pattern >> (1 - s2->h), 0
+						, s2->xmirror, s2->ymirror
+						, x2 - over.left(), y2 - y
+						, 0x10000 << s2->xscale, 0x10000 << s2->yscale);
+
+					for (u8 x = 0; !collision && (x < over.width()); ++x)
+						collision = (b1.pix(0, x) & 0xff) != t_pen1 && (b2.pix(0, x) & 0xff) != t_pen2;
+
+					if (collision)
+						break;
+				}
+			}
 		}
 	}