From a371c8f1e07095e67ff2f4b30e88e8265be43db7 Mon Sep 17 00:00:00 2001
From: Jaklyy <102590697+Jaklyy@users.noreply.github.com>
Date: Sun, 26 Nov 2023 20:17:03 -0500
Subject: [PATCH] first vertex clipped against last becomes last vertex

theory i had.
fixes clipped horizontal line polygons
---
 src/GPU3D.cpp | 38 ++++++++++++++++++++++++++++++++++----
 1 file changed, 34 insertions(+), 4 deletions(-)

diff --git a/src/GPU3D.cpp b/src/GPU3D.cpp
index b00e6fd2..8d7050e2 100644
--- a/src/GPU3D.cpp
+++ b/src/GPU3D.cpp
@@ -769,6 +769,8 @@ int ClipAgainstPlane(const GPU3D& gpu, Vertex* vertices, int nverts, int clipsta
         temp[1] = vertices[1];
     }
 
+    Vertex holdit;
+    bool heldit = false;
     for (int i = clipstart; i < nverts; i++)
     {
         prev = i-1; if (prev < 0) prev = nverts-1;
@@ -782,8 +784,16 @@ int ClipAgainstPlane(const GPU3D& gpu, Vertex* vertices, int nverts, int clipsta
             Vertex* vprev = &vertices[prev];
             if (vprev->Position[comp] <= vprev->Position[3])
             {
-                ClipSegment<comp, 1, attribs>(&temp[c], &vtx, vprev);
-                c++;
+                if (i == 0)
+                {
+                    ClipSegment<comp, 1, attribs>(&holdit, &vtx, vprev);
+                    heldit = true;
+                }
+                else
+                {
+                    ClipSegment<comp, 1, attribs>(&temp[c], &vtx, vprev);
+                    c++;
+                }
             }
 
             Vertex* vnext = &vertices[next];
@@ -797,6 +807,12 @@ int ClipAgainstPlane(const GPU3D& gpu, Vertex* vertices, int nverts, int clipsta
             temp[c++] = vtx;
     }
 
+    if (heldit)
+    {
+        temp[c++] = holdit;
+    }
+    heldit = false;
+
     nverts = c; c = clipstart;
     for (int i = clipstart; i < nverts; i++)
     {
@@ -809,8 +825,17 @@ int ClipAgainstPlane(const GPU3D& gpu, Vertex* vertices, int nverts, int clipsta
             Vertex* vprev = &temp[prev];
             if (vprev->Position[comp] >= -vprev->Position[3])
             {
-                ClipSegment<comp, -1, attribs>(&vertices[c], &vtx, vprev);
-                c++;
+                
+                if (i == 0)
+                {
+                    ClipSegment<comp, -1, attribs>(&holdit, &vtx, vprev);
+                    heldit = true;
+                }
+                else
+                {
+                    ClipSegment<comp, -1, attribs>(&vertices[c], &vtx, vprev);
+                    c++;
+                }
             }
 
             Vertex* vnext = &temp[next];
@@ -823,6 +848,11 @@ int ClipAgainstPlane(const GPU3D& gpu, Vertex* vertices, int nverts, int clipsta
         else
             vertices[c++] = vtx;
     }
+    
+    if (heldit)
+    {
+        vertices[c++] = holdit;
+    }
 
     // checkme
     for (int i = 0; i < c; i++)