From 16828ae0be60e7e6f0ae863ee6c60ea73d12b211 Mon Sep 17 00:00:00 2001
From: Toni Wilen <twilen@winuae.net>
Date: Tue, 3 Mar 2026 19:40:47 +0200
Subject: [PATCH] black level calibration updates

---
 custom.cpp  |  8 ++++----
 drawing.cpp | 42 ++++++++++++++++++++++++++++--------------
 2 files changed, 32 insertions(+), 18 deletions(-)

diff --git a/custom.cpp b/custom.cpp
index 3e239faf..b5d474b0 100644
--- a/custom.cpp
+++ b/custom.cpp
@@ -577,7 +577,7 @@ static int current_linear_hs_hb_dist;
 static uae_u32 agnus_hsstrt_cck, agnus_hsstop_cck;
 static int agnus_hslen_cck, agnus_hslen_cck_prev, agnus_hslen_cck_cnt, current_agnus_hslen_cck;
 static uae_u32 agnus_phsstrt_cck, agnus_phsstop_cck;
-static uae_u32 agnus_pchsstrt_cck, agnus_pchsstop_cck;;
+static uae_u32 agnus_pchsstrt_cck, agnus_pchsstop_cck;
 static bool agnus_pvsync, agnus_pcsync, agnus_csync;
 static int agnus_vb, agnus_pvb;
 static bool agnus_vb_active;
@@ -10709,11 +10709,11 @@ static void draw_line(int ldvpos, bool finalseg)
 		l = &lines[linear_vpos][lof_display];
 	}
 
-	int cs = 0;// (beamcon0 & BEAMCON0_VARHSYEN) ? agnus_phsync_end - agnus_phsync_start : agnus_hsync_end - agnus_hsync_start;
-	int cslen = 10;
+	int calib_start = current_agnus_hslen_cck;
+	int calib_len = 2;
 	draw_denise_line_queue(dvp, nextline_how, rga_denise_cycle_line, rga_denise_cycle_start, rga_denise_cycle, rga_denise_cycle_count_start, rga_denise_cycle_count_end,
 		display_hstart_cyclewait_skip_start, display_hstart_cyclewait_skip_end,
-		wclks, cs, cslen, lof_store, lol, display_hstart_fastmode - display_hstart_cyclewait_start, nosignal_status != 0, finalseg, l);
+		wclks, calib_start, calib_len, lof_store, lol, display_hstart_fastmode - display_hstart_cyclewait_start, nosignal_status != 0, finalseg, l);
 	rga_denise_cycle_count_start = rga_denise_cycle_count_end;
 }
 
diff --git a/drawing.cpp b/drawing.cpp
index 6bfa32e0..49626d8c 100644
--- a/drawing.cpp
+++ b/drawing.cpp
@@ -5453,18 +5453,15 @@ static uae_u8 blc_prev[3];
 static void emulate_black_level_calibration(uae_u32 *b1, uae_u32 *b2, uae_u32 *db, int dtotal, int cstart, int clen)
 {
 	int shift = hresolution + 1;
-	int off;
+	int off = cstart << shift;
+
+	off -= denise_pixtotalskip_start << shift;
 
-	if (cstart < 0) {
-		off = dtotal + cstart;
-	} else {
-		off = cstart;
-	}
 	uae_u32 vv[3] = { 0 };
 	int cnt = 0;
-	for (int i = 0; i < clen; i++) {
-		for (int ii = 0; ii  < (1 << shift); ii++) {
-			int j = (off << shift) + (i << shift) + ii;
+	for (int i = 0; i < (clen << shift); i++) {
+		int j = off + i;
+		if (j >= 0) {
 			uae_u32 v = db[j];
 			uae_u8 vi;
 			vi = (v >> 16) & 0xff;
@@ -5476,8 +5473,18 @@ static void emulate_black_level_calibration(uae_u32 *b1, uae_u32 *b2, uae_u32 *d
 			cnt++;
 		}
 	}
-	db[off << shift] = 0xff0000;
-	db[(off << shift) + (clen << shift) - 1] = 0xff0000;
+	if (!cnt) {
+		return;
+
+	}
+
+#if 1
+	db[off] = 0xff0000;
+	db[off + (clen << shift) - 1] = 0xff0000;
+
+	b1[off] = 0xff0000;
+	b1[off + (clen << shift) - 1] = 0xff0000;
+#endif
 
 	int outc[3];
 	for (int i = 0; i < 3; i++) {
@@ -5487,9 +5494,10 @@ static void emulate_black_level_calibration(uae_u32 *b1, uae_u32 *b2, uae_u32 *d
 //	if (outc[0] > 10 || outc[1] > 10 || outc[2] > 10)
 //		write_log("%02x %02x %02x\n", outc[0], outc[1], outc[2]);
 
+	bool useb2 = b1 != b2 && b2;
 	if (outc[0] <= 3 && outc[1] <= 3 && outc[2] <= 3) {
 		memcpy(b1, db, (dtotal * sizeof(uae_u32)) << shift);
-		if (b1 != b2) {
+		if (useb2) {
 			memcpy(b2, db, (dtotal * sizeof(uae_u32)) << shift);
 		}
 	} else {
@@ -5505,14 +5513,20 @@ static void emulate_black_level_calibration(uae_u32 *b1, uae_u32 *b2, uae_u32 *d
 						if (c[j] <= outc[j]) {
 							c[j] = 0;
 						} else {
-							c[j] = (c[j] - outc[j]) * 256 / outc[j];
+							int cc = c[j] + outc[j];
+							if (cc >= 256) {
+								cc = 255;
+							}
+							c[j] = cc;
 						}
 					}
 				}
 				v = (c[0] << 16) | (c[1] << 8) | (c[2] << 0);
 			}
 			*b1++ = v;
-			*b2++ = v;
+			if (useb2) {
+				*b2++ = v;
+			}
 		}
 	}
 }
-- 
2.47.3