From 012527fc4e31f1970fca83dfc0d6687f03b2cd99 Mon Sep 17 00:00:00 2001
From: TC1995 <mariogplayer90@gmail.com>
Date: Sat, 23 Dec 2023 15:02:15 +0100
Subject: [PATCH] MGA flicker fixes. It's time to end the flickers once and for
 all by making the start address correctly emulated in vblank_start when in
 power graphics mode.

---
 src/video/vid_mga.c | 81 ++++++++++++++++++---------------------------
 1 file changed, 32 insertions(+), 49 deletions(-)

diff --git a/src/video/vid_mga.c b/src/video/vid_mga.c
index 2720bea68..98e45fd2f 100644
--- a/src/video/vid_mga.c
+++ b/src/video/vid_mga.c
@@ -722,27 +722,6 @@ mystique_out(uint16_t addr, uint8_t val, void *priv)
             if (mystique->crtcext_idx < 6)
                 mystique->crtcext_regs[mystique->crtcext_idx] = val;
 
-            if (mystique->crtcext_idx == 0 && (mystique->crtcext_regs[3] & CRTCX_R3_MGAMODE))
-            {
-                svga->rowoffset     = svga->crtc[0x13] | ((mystique->crtcext_regs[0] & CRTCX_R0_OFFSET_MASK) << 4);
-                svga->rowoffset <<= 1;
-                svga->ma_latch      = ((mystique->crtcext_regs[0] & CRTCX_R0_STARTADD_MASK) << 16) | (svga->crtc[0xc] << 8) | svga->crtc[0xd];
-                if (mystique->pci_regs[0x41] & (OPTION_INTERLEAVE >> 8)) {
-                    svga->rowoffset <<= 1;
-                    svga->ma_latch <<= 1;
-                }
-                if (mystique->type >= MGA_1064SG) {
-                    svga->ma_latch <<= 1;
-                    if (svga->ma_latch != mystique->ma_latch_old) {
-                        if (svga->interlace && svga->oddeven)
-                            svga->maback = (svga->maback - (mystique->ma_latch_old << 2)) + (svga->ma_latch << 2) + (svga->rowoffset << 1);
-                        else
-                            svga->maback = (svga->maback - (mystique->ma_latch_old << 2)) + (svga->ma_latch << 2);
-                        mystique->ma_latch_old = svga->ma_latch;
-                    }
-                }
-            }
-
             if (mystique->crtcext_idx == 4) {
                 if (svga->gdcreg[6] & 0xc) {
                     /*64k banks*/
@@ -829,6 +808,33 @@ mystique_line_compare(svga_t *svga)
     return 0;
 }
 
+static void
+mystique_vblank_start(svga_t *svga)
+{
+    mystique_t *mystique = (mystique_t *) svga->priv;
+
+    if (mystique->crtcext_regs[3] & CRTCX_R3_MGAMODE) {
+        svga->ma_latch      = ((mystique->crtcext_regs[0] & CRTCX_R0_STARTADD_MASK) << 16) | (svga->crtc[0xc] << 8) | svga->crtc[0xd];
+        if (mystique->pci_regs[0x41] & (OPTION_INTERLEAVE >> 8))
+            svga->ma_latch <<= 1;
+
+        if (mystique->type >= MGA_1064SG) {
+            /*Mystique, unlike most SVGA cards, allows display start to take
+              effect mid-screen*/
+            svga->ma_latch <<= 1;
+            /* Only change maback so the new display start will take effect on the next
+               horizontal retrace. */
+            if (svga->ma_latch != mystique->ma_latch_old) {
+                if (svga->interlace && svga->oddeven)
+                    svga->maback = (svga->maback - (mystique->ma_latch_old << 2)) + (svga->ma_latch << 2) + (svga->rowoffset << 1);
+                else
+                    svga->maback = (svga->maback - (mystique->ma_latch_old << 2)) + (svga->ma_latch << 2);
+                mystique->ma_latch_old = svga->ma_latch;
+            }
+        }
+    }
+}
+
 static void
 mystique_vsync_callback(svga_t *svga)
 {
@@ -896,39 +902,14 @@ mystique_recalctimings(svga_t *svga)
     if (mystique->crtcext_regs[3] & CRTCX_R3_MGAMODE) {
         svga->lowres        = 0;
         svga->char_width    = 8;
-        svga->hdisp         = (svga->crtc[1] + 1) * 8;
+        svga->hdisp         = (svga->crtc[1] + 1) << 3;
         svga->hdisp_time    = svga->hdisp;
         svga->rowoffset     = svga->crtc[0x13] | ((mystique->crtcext_regs[0] & CRTCX_R0_OFFSET_MASK) << 4);
-        svga->ma_latch      = ((mystique->crtcext_regs[0] & CRTCX_R0_STARTADD_MASK) << 16) | (svga->crtc[0xc] << 8) | svga->crtc[0xd];
-        if (mystique->pci_regs[0x41] & (OPTION_INTERLEAVE >> 8)) {
+
+        if (mystique->pci_regs[0x41] & (OPTION_INTERLEAVE >> 8))
             svga->rowoffset <<= 1;
-            svga->ma_latch <<= 1;
-        }
 
         if (mystique->type >= MGA_1064SG) {
-            /*Mystique, unlike most SVGA cards, allows display start to take
-              effect mid-screen*/
-            svga->ma_latch <<= 1;
-#ifdef CHANGE_MA
-            if (svga->ma_latch != mystique->ma_latch_old) {
-                if (svga->interlace && svga->oddeven)
-                    svga->ma = svga->maback = (svga->maback - (mystique->ma_latch_old << 2)) + (svga->ma_latch << 2) + (svga->rowoffset << 1);
-                else
-                    svga->ma = svga->maback = (svga->maback - (mystique->ma_latch_old << 2)) + (svga->ma_latch << 2);
-                mystique->ma_latch_old = svga->ma_latch;
-            }
-#else
-            /* Only change maback so the new display start will take effect on the next
-               horizontal retrace. */
-            if (svga->ma_latch != mystique->ma_latch_old) {
-                if (svga->interlace && svga->oddeven)
-                    svga->maback = (svga->maback - (mystique->ma_latch_old << 2)) + (svga->ma_latch << 2) + (svga->rowoffset << 1);
-                else
-                    svga->maback = (svga->maback - (mystique->ma_latch_old << 2)) + (svga->ma_latch << 2);
-                mystique->ma_latch_old = svga->ma_latch;
-            }
-#endif
-
             svga->rowoffset <<= 1;
             switch (mystique->xmulctrl & XMULCTRL_DEPTH_MASK) {
                 case XMULCTRL_DEPTH_8:
@@ -979,9 +960,11 @@ mystique_recalctimings(svga_t *svga)
         }
         svga->packed_chain4 = 1;
         svga->line_compare = mystique_line_compare;
+        svga->vblank_start = mystique_vblank_start;
     } else {
         svga->packed_chain4 = 0;
         svga->line_compare  = NULL;
+        svga->vblank_start  = NULL;
         if (mystique->type >= MGA_1064SG)
             svga->bpp = 8;
     }