From 84b9af3e05bb29f23afbcf900d2d3b8cb5b675ca Mon Sep 17 00:00:00 2001
From: SarahW <pcem@pcem-emulator.co.uk>
Date: Mon, 7 Jun 2021 19:51:30 +0100
Subject: [PATCH] Use correct value for Y swap origin on Voodoo Banshee/3.
 Fixes issues sometimes seen when running in low resolutions, ie below
 640x480.

---
 src/vid_voodoo_banshee.c | 4 ++++
 src/vid_voodoo_blitter.c | 6 ++++--
 src/vid_voodoo_common.h  | 2 ++
 src/vid_voodoo_render.c  | 5 +++--
 4 files changed, 13 insertions(+), 4 deletions(-)

diff --git a/src/vid_voodoo_banshee.c b/src/vid_voodoo_banshee.c
index a549270..34eaffd 100644
--- a/src/vid_voodoo_banshee.c
+++ b/src/vid_voodoo_banshee.c
@@ -205,6 +205,9 @@ enum
 #define VIDSERIAL_I2C_SCK_R (1 << 26)
 #define VIDSERIAL_I2C_SDA_R (1 << 27)
 
+#define MISCINIT0_Y_ORIGIN_SWAP_SHIFT (18)
+#define MISCINIT0_Y_ORIGIN_SWAP_MASK (0xfff << MISCINIT0_Y_ORIGIN_SWAP_SHIFT)
+
 static uint32_t banshee_status(banshee_t *banshee);
 
 static void banshee_out(uint16_t addr, uint8_t val, void *p)
@@ -550,6 +553,7 @@ static void banshee_ext_outl(uint16_t addr, uint32_t val, void *p)
 
                 case Init_miscInit0:
                 banshee->miscInit0 = val;
+                voodoo->y_origin_swap = (val & MISCINIT0_Y_ORIGIN_SWAP_MASK) >> MISCINIT0_Y_ORIGIN_SWAP_SHIFT;
                 break;
                 case Init_miscInit1:
                 banshee->miscInit1 = val;
diff --git a/src/vid_voodoo_blitter.c b/src/vid_voodoo_blitter.c
index 01048f9..af7e204 100644
--- a/src/vid_voodoo_blitter.c
+++ b/src/vid_voodoo_blitter.c
@@ -409,8 +409,10 @@ void voodoo_fastfill(voodoo_t *voodoo, voodoo_params_t *params)
 
         if (params->fbzMode & (1 << 17))
         {
-                high_y = voodoo->v_disp - params->clipLowY;
-                low_y = voodoo->v_disp - params->clipHighY;
+                int y_origin = (voodoo->type >= VOODOO_BANSHEE) ? (voodoo->y_origin_swap+1) : voodoo->v_disp;
+
+                high_y = y_origin - params->clipLowY;
+                low_y = y_origin - params->clipHighY;
         }
         else
         {
diff --git a/src/vid_voodoo_common.h b/src/vid_voodoo_common.h
index df261af..dd760ae 100644
--- a/src/vid_voodoo_common.h
+++ b/src/vid_voodoo_common.h
@@ -456,6 +456,8 @@ typedef struct voodoo_t
         uint32_t tile_base, tile_stride;
         int tile_stride_shift, tile_x, tile_x_real;
 
+        int y_origin_swap;
+
         int read_time, write_time, burst_time;
 
         pc_timer_t wake_timer;
diff --git a/src/vid_voodoo_render.c b/src/vid_voodoo_render.c
index 2116180..503829d 100644
--- a/src/vid_voodoo_render.c
+++ b/src/vid_voodoo_render.c
@@ -682,6 +682,7 @@ static void voodoo_half_triangle(voodoo_t *voodoo, voodoo_params_t *params, vood
         uint8_t (*voodoo_draw)(voodoo_state_t *state, voodoo_params_t *params, int x, int real_y);
 #endif
         int y_diff = SLI_ENABLED ? 2 : 1;
+        int y_origin = (voodoo->type >= VOODOO_BANSHEE) ? voodoo->y_origin_swap : (voodoo->v_disp-1);
 
         if ((params->textureMode[0] & TEXTUREMODE_MASK) == TEXTUREMODE_PASSTHROUGH ||
             (params->textureMode[0] & TEXTUREMODE_LOCAL_MASK) == TEXTUREMODE_LOCAL)
@@ -746,7 +747,7 @@ static void voodoo_half_triangle(voodoo_t *voodoo, voodoo_params_t *params, vood
                 int test_y;
 
                 if (params->fbzMode & (1 << 17))
-                        test_y = (voodoo->v_disp-1) - state->y;
+                        test_y = y_origin - state->y;
                 else
                         test_y = state->y;
 
@@ -811,7 +812,7 @@ static void voodoo_half_triangle(voodoo_t *voodoo, voodoo_params_t *params, vood
                         x2 = (state->vertexBx << 12) + ((state->dxBC * (real_y - state->vertexBy)) >> 4);
 
                 if (params->fbzMode & (1 << 17))
-                        real_y = (voodoo->v_disp-1) - (real_y >> 4);
+                        real_y = y_origin - (real_y >> 4);
                 else
                         real_y >>= 4;