From d8669a522710beae21dca7282293503c260dbfe6 Mon Sep 17 00:00:00 2001
From: OBattler <oubattler@gmail.com>
Date: Mon, 30 Jun 2025 00:36:00 +0200
Subject: [PATCH] (S)VGA: Recalculate pel panning on every line instead of on
 every frame.

---
 src/include/86box/vid_svga.h |  1 +
 src/video/vid_svga.c         | 53 ++++++++++++++++++++----------------
 2 files changed, 31 insertions(+), 23 deletions(-)

diff --git a/src/include/86box/vid_svga.h b/src/include/86box/vid_svga.h
index 8a18f0865..78e025746 100644
--- a/src/include/86box/vid_svga.h
+++ b/src/include/86box/vid_svga.h
@@ -137,6 +137,7 @@ typedef struct svga_t {
     int ps_bit_bug;
     int ati_4color;
     int vblankend;
+    int panning_blank;
 
     /*The three variables below allow us to implement memory maps like that seen on a 1MB Trio64 :
       0MB-1MB - VRAM
diff --git a/src/video/vid_svga.c b/src/video/vid_svga.c
index 2073fb8c0..e4a6d9efc 100644
--- a/src/video/vid_svga.c
+++ b/src/video/vid_svga.c
@@ -1435,10 +1435,8 @@ svga_poll(void *priv)
                 svga->memaddr_backup = (svga->memaddr_backup << 2);
 
                 svga->scanline = 0;
-                if (svga->attrregs[0x10] & 0x20) {
-                    svga->scrollcache = 0;
-                    svga->x_add       = svga->left_overscan;
-                }
+                if (svga->attrregs[0x10] & 0x20)
+                    svga->panning_blank = 1;
             }
         }
         if (svga->vc == svga->dispend) {
@@ -1526,25 +1524,6 @@ svga_poll(void *priv)
             svga->dispon   = 1;
             svga->displine = (svga->interlace && svga->oddeven) ? 1 : 0;
 
-            svga->scrollcache = (svga->attrregs[0x13] & 0x0f);
-            if (!(svga->gdcreg[6] & 1) && !(svga->attrregs[0x10] & 1)) { /*Text mode*/
-                if (svga->seqregs[1] & 1)
-                    svga->scrollcache &= 0x07;
-                else {
-                    svga->scrollcache++;
-                    if (svga->scrollcache > 8)
-                        svga->scrollcache = 0;
-                }
-            } else if ((svga->render == svga_render_2bpp_lowres) || (svga->render == svga_render_2bpp_highres) || (svga->render == svga_render_4bpp_lowres) || (svga->render == svga_render_4bpp_highres))
-                svga->scrollcache &= 0x07;
-            else
-                svga->scrollcache = (svga->scrollcache & 0x06) >> 1;
-
-            if ((svga->seqregs[1] & 8) || (svga->render == svga_render_8bpp_lowres))
-                svga->scrollcache <<= 1;
-
-            svga->x_add = svga->left_overscan - svga->scrollcache;
-
             svga->linecountff = 0;
 
             svga->hwcursor_on    = 0;
@@ -1555,9 +1534,37 @@ svga_poll(void *priv)
 
             svga->overlay_on    = 0;
             svga->overlay_latch = svga->overlay;
+
+            svga->panning_blank = 0;
         }
+
         if (svga->scanline == (svga->crtc[10] & 31))
             svga->cursorvisible = 1;
+
+        if (svga->panning_blank) {
+            svga->scrollcache = 0;
+            svga->x_add       = svga->left_overscan;
+        } else {
+            svga->scrollcache = (svga->attrregs[0x13] & 0x0f);
+            if (!(svga->gdcreg[6] & 1) && !(svga->attrregs[0x10] & 1)) { /*Text mode*/
+                if (svga->seqregs[1] & 1)
+                    svga->scrollcache &= 0x07;
+                else {
+                    svga->scrollcache++;
+                    if (svga->scrollcache > 8)
+                        svga->scrollcache = 0;
+                }
+            } else if ((svga->render == svga_render_2bpp_lowres) || (svga->render == svga_render_2bpp_highres) ||
+                       (svga->render == svga_render_4bpp_lowres) || (svga->render == svga_render_4bpp_highres))
+                svga->scrollcache &= 0x07;
+            else
+                svga->scrollcache = (svga->scrollcache & 0x06) >> 1;
+
+            if ((svga->seqregs[1] & 8) || (svga->render == svga_render_8bpp_lowres))
+                svga->scrollcache <<= 1;
+
+            svga->x_add = svga->left_overscan - svga->scrollcache;
+        }
     }
 }