From 6f22d58a4f4cbc10e4f513e8a9d32735def7d17e Mon Sep 17 00:00:00 2001
From: Cacodemon345 <wahil1976@outlook.com>
Date: Mon, 19 Feb 2024 16:01:49 +0600
Subject: [PATCH] C&T 69000: Fix pattern drawing in 16-bpp modes

---
 src/video/vid_chips_69000.c | 20 +++++++++++++++++---
 1 file changed, 17 insertions(+), 3 deletions(-)

diff --git a/src/video/vid_chips_69000.c b/src/video/vid_chips_69000.c
index 6060010560..0708c7bc56 100644
--- a/src/video/vid_chips_69000.c
+++ b/src/video/vid_chips_69000.c
@@ -881,6 +881,7 @@ chips_69000_process_pixel(chips_69000_t* chips, uint32_t pixel)
     uint32_t dest_pixel = 0;
     uint32_t dest_addr = chips->bitblt_running.bitblt.destination_addr + (chips->bitblt_running.y * chips->bitblt_running.bitblt.destination_span) + (chips->bitblt_running.x * chips->bitblt_running.bytes_per_pixel);
     uint8_t vert_pat_alignment = (chips->bitblt_running.bitblt.bitblt_control >> 20) & 7;
+    uint8_t orig_dest_addr_bit = chips->bitblt_running.bitblt.destination_addr & 1;
 
     switch (chips->bitblt_running.bytes_per_pixel) {
         case 1: /* 8 bits-per-pixel. */
@@ -903,8 +904,9 @@ chips_69000_process_pixel(chips_69000_t* chips, uint32_t pixel)
             }
     }
 
-    /* TODO: Find out from where it actually pulls the exact pattern x and y values. */
-    /* Also: is horizontal pattern alignment a requirement? */
+    if (chips->bitblt_running.bytes_per_pixel == 2) {
+        chips->bitblt_running.bitblt.destination_addr >>= 1;
+    }
     if (chips->bitblt_running.bitblt.bitblt_control & (1 << 18)) {
         uint8_t is_true = 0;
         if (chips->bitblt_running.bitblt.bitblt_control & (1 << 19))
@@ -915,6 +917,10 @@ chips_69000_process_pixel(chips_69000_t* chips, uint32_t pixel)
         is_true = !!(pattern_data & (1 << (7 - ((chips->bitblt_running.bitblt.destination_addr + chips->bitblt_running.x) & 7))));
 
         if (!is_true && (chips->bitblt_running.bitblt.bitblt_control & (1 << 17))) {
+            if (chips->bitblt_running.bytes_per_pixel == 2) {
+                chips->bitblt_running.bitblt.destination_addr <<= 1;
+                chips->bitblt_running.bitblt.destination_addr |= orig_dest_addr_bit;
+            }
             return;
         }
 
@@ -928,9 +934,13 @@ chips_69000_process_pixel(chips_69000_t* chips, uint32_t pixel)
                                                         + (((chips->bitblt_running.bitblt.destination_addr & 7) + chips->bitblt_running.x) & 7), chips);
         }
         if (chips->bitblt_running.bytes_per_pixel == 2) {
-            pattern_pixel = chips_69000_readw_linear(chips->bitblt_running.bitblt.pat_addr
+            pattern_pixel = chips_69000_readb_linear(chips->bitblt_running.bitblt.pat_addr
                                                         + (2 * 8 * ((vert_pat_alignment + chips->bitblt_running.y) & 7))
                                                         + (2 * (((chips->bitblt_running.bitblt.destination_addr & 7) + chips->bitblt_running.x) & 7)), chips);
+
+            pattern_pixel |= chips_69000_readb_linear(chips->bitblt_running.bitblt.pat_addr
+                                                        + (2 * 8 * ((vert_pat_alignment + chips->bitblt_running.y) & 7))
+                                                        + (2 * (((chips->bitblt_running.bitblt.destination_addr & 7) + chips->bitblt_running.x) & 7)) + 1, chips) << 8;
         }
         if (chips->bitblt_running.bytes_per_pixel == 3) {
             pattern_pixel = chips_69000_readb_linear(chips->bitblt_running.bitblt.pat_addr
@@ -946,6 +956,10 @@ chips_69000_process_pixel(chips_69000_t* chips, uint32_t pixel)
                                                         + (3 * (((chips->bitblt_running.bitblt.destination_addr & 7) + chips->bitblt_running.x) & 7)) + 2, chips) << 16;
         }
     }
+    if (chips->bitblt_running.bytes_per_pixel == 2) {
+        chips->bitblt_running.bitblt.destination_addr <<= 1;
+        chips->bitblt_running.bitblt.destination_addr |= orig_dest_addr_bit;
+    }
 
     if (chips->bitblt_running.bitblt.bitblt_control & (1 << 14)) {
         switch ((chips->bitblt_running.bitblt.bitblt_control >> 15) & 3) {