From: dinkc64 <terra79pin@yahoo.com>
Date: Fri, 13 Mar 2020 23:26:09 +0000 (-0400)
Subject: draw.c, DrawLayer(): impl. proper linescroll, fixes issue #56
X-Git-Tag: v2.00~668^2~1^2
X-Git-Url: https://notaz.gp2x.de/cgi-bin/gitweb.cgi?a=commitdiff_plain;h=ce32676eb890d4b4100e5d639514bfe7d6363bb4;p=picodrive.git

draw.c, DrawLayer(): impl. proper linescroll, fixes issue #56
---

diff --git a/pico/draw.c b/pico/draw.c
index 680de3da..e5287b4e 100644
--- a/pico/draw.c
+++ b/pico/draw.c
@@ -411,6 +411,7 @@ static void DrawLayer(int plane_sh, int *hcache, int cellskip, int maxcells,
 {
   struct PicoVideo *pvid=&Pico.video;
   const char shift[4]={5,6,5,7}; // 32,64 or 128 sized tilemaps (2 is invalid)
+  const unsigned char h_masks[4] = { 0x00, 0x07, 0xf8, 0xff };
   struct TileStrip ts;
   int width, height, ymask;
   int vscroll, htab;
@@ -437,8 +438,7 @@ static void DrawLayer(int plane_sh, int *hcache, int cellskip, int maxcells,
   else            ts.nametab=(pvid->reg[2]&0x38)<< 9; // A
 
   htab=pvid->reg[13]<<9; // Horizontal scroll table address
-  if ( pvid->reg[11]&2)     htab+=est->DrawScanline<<1; // Offset by line
-  if ((pvid->reg[11]&1)==0) htab&=~0xf; // Offset by tile
+  htab+=(est->DrawScanline&h_masks[pvid->reg[11]&3])<<1; // Point to line (masked)
   htab+=plane_sh&1; // A or B
 
   // Get horizontal scroll value, will be masked later