From da31af92029af5f9db3c9fcc226414e3789f2682 Mon Sep 17 00:00:00 2001
From: StapleButter <thetotalworm@gmail.com>
Date: Sat, 29 Apr 2017 00:20:04 +0200
Subject: [PATCH] fix Z-buffering. not really clean, and not perfectly
 accurate.

---
 src/GPU3D.cpp      |  2 +-
 src/GPU3D.h        |  1 +
 src/GPU3D_Soft.cpp | 16 ++++++++--------
 3 files changed, 10 insertions(+), 9 deletions(-)

diff --git a/src/GPU3D.cpp b/src/GPU3D.cpp
index a63193f1..72e71793 100644
--- a/src/GPU3D.cpp
+++ b/src/GPU3D.cpp
@@ -839,6 +839,7 @@ void SubmitPolygon()
     poly->YTop = ytop; poly->YBottom = ybot;
     poly->XTop = xtop; poly->XBottom = xbot;
     poly->WShift = wshift;
+    poly->WBuffer = (FlushAttributes & 0x2);
 
     for (int i = 0; i < nverts; i++)
     {
@@ -849,7 +850,6 @@ void SubmitPolygon()
         if (FlushAttributes & 0x2)
             z = w << wshift;
         else
-            //z = vtx->Position[2]+0x7FFFFF;//((vtx->Position[2] + (w<<wshift)) * 0x1000) / (w<<(wshift+1));
             z = (((s64)vtx->Position[2] * 0x800000) / (w << wshift)) + 0x7FFEFF;
 
         // checkme
diff --git a/src/GPU3D.h b/src/GPU3D.h
index 79287f7c..fdb85f8c 100644
--- a/src/GPU3D.h
+++ b/src/GPU3D.h
@@ -46,6 +46,7 @@ typedef struct
     s32 FinalZ[10];
     s32 FinalW[10];
     u8 WShift;
+    bool WBuffer;
 
     u32 Attr;
     u32 TexParam;
diff --git a/src/GPU3D_Soft.cpp b/src/GPU3D_Soft.cpp
index 649f01f0..55dd9061 100644
--- a/src/GPU3D_Soft.cpp
+++ b/src/GPU3D_Soft.cpp
@@ -129,14 +129,14 @@ public:
             return y0 + (((y1 - y0) * x) / xdiff);
     }
 
-    s32 InterpolateZ(s32 y0, s32 y1)
+    s32 InterpolateZ(s32 z0, s32 z1, bool wbuffer)
     {
-        if (xdiff == 0) return y0;
+        if (xdiff == 0) return z0;
 
-        if (wdiff != 0)
-            return y0 + (((s64)(y1 - y0) * yfactor) >> shift);
+        if ((wdiff != 0) && wbuffer)
+            return z0 + (((s64)(z1 - z0) * yfactor) >> shift);
         else
-            return y0 + (((s64)(y1 - y0) * x) / xdiff);
+            return z0 + (((s64)(z1 - z0) * x) / xdiff);
     }
 
 private:
@@ -806,8 +806,8 @@ void RenderPolygon(Polygon* polygon)
         s32 wl = slopeL.Interp.Interpolate(polygon->FinalW[lcur], polygon->FinalW[lnext]);
         s32 wr = slopeR.Interp.Interpolate(polygon->FinalW[rcur], polygon->FinalW[rnext]);
 
-        s32 zl = slopeL.Interp.InterpolateZ(polygon->FinalZ[lcur], polygon->FinalZ[lnext]);
-        s32 zr = slopeR.Interp.InterpolateZ(polygon->FinalZ[rcur], polygon->FinalZ[rnext]);
+        s32 zl = slopeL.Interp.InterpolateZ(polygon->FinalZ[lcur], polygon->FinalZ[lnext], polygon->WBuffer);
+        s32 zr = slopeR.Interp.InterpolateZ(polygon->FinalZ[rcur], polygon->FinalZ[rnext], polygon->WBuffer);
 
         // if the left and right edges are swapped, render backwards.
         // note: we 'forget' to swap the xmajor flags, on purpose
@@ -928,7 +928,7 @@ void RenderPolygon(Polygon* polygon)
 
             interpX.SetX(x);
 
-            s32 z = interpX.InterpolateZ(zl, zr);
+            s32 z = interpX.InterpolateZ(zl, zr, polygon->WBuffer);
 
             if (polygon->IsShadowMask)
             {