given clip 0,0 639, 479 and a triangle start at 479 y_count 480 this
clipped off-by-one?

  - René Rebe <rene@exactcode.de>

--- ./src/vid_s3_virge.c.vanilla	2018-11-02 21:34:23.001923446 +0100
+++ ./src/vid_s3_virge.c	2018-11-02 21:36:33.253917430 +0100
@@ -2975,8 +2975,8 @@
                         z_offset -= s3d_tri->z_str;
                         y_count -= diff_y;
                 }
-                if ((state->y - y_count) < s3d_tri->clip_t)
-                        y_count = state->y - s3d_tri->clip_t;
+                if ((state->y + 1 - y_count) < s3d_tri->clip_t)
+                        y_count = state->y - s3d_tri->clip_t + 1;
         }
         
         for (; y_count > 0; y_count--)
@@ -2990,7 +2990,7 @@
                         xe--;
                 }
 
-                if (x != xe && ((x_dir > 0 && x < xe) || (x_dir < 0 && x > xe)))
+                if ((x_dir > 0 && x <= xe) || (x_dir < 0 && x >= xe))
                 {
                         uint32_t dest_addr, z_addr;
                         int dx = (x_dir > 0) ? ((31 - ((state->x1-1) >> 15)) & 0x1f) : (((state->x1-1) >> 15) & 0x1f);
@@ -3069,7 +3069,7 @@
                         dest_addr = dest_offset + (x * (bpp + 1));
                         z_addr = z_offset + (x << 1);
 
-                        for (; x != xe; x = (x + x_dir) & 0xfff)
+                        for (; (x_dir > 0 && x <= xe) || (x_dir < 0 && x >= xe); x = (x + x_dir) & 0xfff)
                         {
                                 int update = 1;
                                 uint16_t src_z = 0;